Maternal and neonatal outcomes among pregnant women with 2009 pandemic influenza A(H1N1) illness in Florida, 2009-2010: a population-based cohort study

Influenza in Pregnancy: Maternal, Obstetric, and Fetal Implications, Diagnosis, and Management

Influenza(flu) in pregnancy is associated with higher rates of hospitalization, ICU admission, and death and with increased odds of congenital anomalies and stillbirth, but not preterm birth. Clinical manifestations of flu in pregnancy are the same as nonpregnant patients. Pregnant individuals with flu-like symptoms or flu exposure should be treated with antivirals. Diagnostic testing is not needed. Oseltamivir is the mainstay of treatment(and prophylaxis), and when given within 48 hours of symptom onset, it decreases morbidity and mortality. Influenza is associated with worse maternal, obstetric, and neonatal outcomes. These risks are mitigated by early oseltamivir treatment and maternal vaccination; hence the recommendation for universal vaccination in pregnancy.

Brain region-specific alterations in gene expression trajectories in the offspring born from influenza A virus infected mice

Influenza A virus (IAV) infection during pregnancy can increase the risk for neurodevelopmental disorders in the offspring, however, the underlying neurobiological mechanisms are largely unknown. To recapitulate viral infection, preclinical studies have traditionally focused on using synthetic viral mimetics, rather than live IAV, to examine consequences of maternal immune activation (MIA)-dependent processes on offspring. In contrast, few studies have used live IAV to assess effects on global gene expression, and none to date have addressed whether moderate IAV, mimicking seasonal influenza disease, alters normal gene expression trajectories in different brain regions across different stages of development. Herein, we show that moderate IAV infection during pregnancy, which causes mild maternal disease and no overt foetal complications in utero, induces lasting effects on the offspring into adulthood. We observed behavioural changes in adult offspring, including disrupted prepulse inhibition, dopaminergic hyper-responsiveness, and spatial recognition memory deficits. Gene profiling in the offspring brain from neonate to adolescence revealed persistent alterations to normal gene expression trajectories in the prefronal cortex, hippocampus, hypothalamus and cerebellum. Alterations were found in genes involved in inflammation and neurogenesis, which were predominately dysregulated in neonatal and early adolescent offspring. Notably, late adolescent offspring born from IAV infected mice displayed altered microglial morphology in the hippocampus. In conclusion, we show that moderate IAV during pregnancy perturbs neurodevelopmental trajectories in the offspring, including alterations in the neuroinflammatory gene expression profile and microglial number and morphology in the hippocampus, resulting in behavioural changes in adult offspring. Such early perturbations may underlie the vulnerability in human offspring for the later development of neurodevelopmental disorders, including schizophrenia. Our work highlights the importance of using live IAV in developing novel preclinical models that better recapitulate the real-world impact of inflammatory insults during pregnancy on offspring neurodevelopmental trajectories and disease susceptibility later in life.

Evaluation of intentions to get vaccinated against influenza, COVID 19, pertussis and to get a future vaccine against respiratory syncytial virus in pregnant women

INTRODUCTION

Pregnant women (PW) are at increased risk of complications due to seasonal influenza and Covid-19. Immunization during pregnancy against pertussis and respiratory syncytial virus (RSV) protects newborns from severe diseases. Our aim was to assess intentions to get vaccinated against seasonal influenza, COVID-19, pertussis and RSV in PW and to identify factors associated with intentions.

METHODS

Cross-sectional survey in PW followed at a University Hospital in France assessing their knowledge, and attitudes toward vaccination against influenza, Covid-19, and RSV during pregnancy. Primary outcome was intention to receive each vaccine or potential vaccine. Univariable and multivariable analysis were carried out to identify factors associated with intentions to get vaccinated for each vaccine.

RESULTS

Among the 1199 PW followed during the study period, 310 completed the questionnaire. Intentions to get vaccinated were respectively 43.9 %, 36.8 %, 36.1 % and 39.4 % against influenza, Covid-19, pertussis and RSV. Overall confidence in vaccines using 5C-model, recommendation by a healthcare professional (HCP), good knowledge about diseases and vaccines and previous influenza vaccination were associated with flu vaccine acceptance with respective adjusted odds ratios and 95 % Confidence Intervals (aOR) 1.69 (1.09-2.61) by one-point increase in confidence score, 4.89 (2.24-10.7), 1.56 by one-point increase in knowledge score (1.26-1.93), 13.5 and (5.3-34.3). Confidence was also associated with Covid-19 and RSV vaccine acceptance with respective aOR and 95 % CI 2.63 (1.7-4.07) and 1.92 (1.3-2.84). For pertussis, previous flu vaccination or pertussis vaccination in the last 5 years were predictors of pertussis vaccine acceptance during the pregnancy with respective aOR and 95 % CI 1.97 (1.1-3.84) and 2.9 (1.6-5.18).

CONCLUSION

Confidence is associated with seasonal influenza, COVID-19 and RSV vaccines acceptance in pregnant women. Receiving a recommendation from a HCP was strongly associated with acceptance of influenza vaccine. Recent vaccination against pertussis was not a barrier to pertussis vaccine acceptance during pregnancy.

Usefulness of linked data for infectious disease events: a systematic review

Surveillance is a key public health function to enable early detection of infectious disease events and inform public health action. Data linkage may improve the depth of data for response to infectious disease events. This study aimed to describe the uses of linked data for infectious disease events. A systematic review was conducted using Pubmed, CINAHL and Web of Science. Studies were included if they used data linkage for an acute infectious disease event (e.g. outbreak of disease). We summarised the event, study aims and designs; data sets; linkage methods; outcomes reported; and benefits and limitations. Fifty-four studies were included. Uses of linkage for infectious disease events included assessment of severity of disease and risk factors; improved case finding and contact tracing; and vaccine uptake, safety and effectiveness. The ability to conduct larger scale population level studies was identified as a benefit, in particular for rarer exposures, risk factors or outcomes. Limitations included timeliness, data quality and inability to collect additional variables. This review demonstrated multiple uses of data linkage for infectious disease events. As infectious disease events occur without warning, there is a need to establish pre-approved protocols and the infrastructure for data-linkage to enhance information available during an event.

Sex and Gender in Lung Diseases and Sleep Disorders: A State-of-the-Art Review: Part 2

There is now ample evidence that differences in sex and gender contribute to the incidence, susceptibility, presentation, diagnosis, and clinical course of many lung diseases. Some conditions are more prevalent in women, such as pulmonary arterial hypertension and sarcoidosis. Some life stages-such as pregnancy-are unique to women and can affect the onset and course of lung disease. Clinical presentation may differ as well, such as the higher number of exacerbations experienced by women with cystic fibrosis (CF), more fatigue in women with sarcoidosis, and more difficulty in achieving smoking cessation. Outcomes such as mortality may be different as well, as indicated by the higher mortality in women with CF. In addition, response to therapy and medication safety may also differ by sex, and yet, pharmacogenomic factors are often not adequately addressed in clinical trials. Various aspects of lung/sleep biology and pathobiology are impacted by female sex and female reproductive transitions. Differential gene expression or organ development can be impacted by these biological differences. Understanding these differences is the first step in moving toward precision medicine for all patients. This article is the second part of a state-of-the-art review of specific effects of sex and gender focused on epidemiology, disease presentation, risk factors, and management of selected lung diseases. We review the more recent literature and focus on guidelines incorporating sex and gender differences in pulmonary hypertension, CF and non-CF bronchiectasis, sarcoidosis, restless legs syndrome and insomnia, and critical illness. We also provide a summary of the effects of pregnancy on lung diseases and discuss the impact of sex and gender on tobacco use and treatment of nicotine use disorder.

Neurodevelopment in infants with antenatal or early neonatal exposure to SARS-CoV-2

BACKGROUND

Antenatal and neonatal viral exposure may put the developing brain at risk for abnormal neurodevelopment. A clinical program at Children's National Hospital provides detailed follow-up of infants with in utero or neonatal SARS-CoV-2 exposure.

AIMS

To determine impact of early SARS-CoV-2 exposure on neurodevelopment.

STUDY DESIGN

We performed a prospective observational study of infant evaluations between 3/2020 and 11/2021. Demographics, pregnancy and birth details, SARS-CoV-2 data, specialty consultations, and NICU records were extracted from infants' medical records. Infants had neurologic exams and developmental screening with Ages and Stages Questionnaire (ASQ). Correlations between SARS-CoV-2 exposure type and neurodevelopmental outcomes were analyzed.

SUBJECTS

Thirty-four infants evaluated in the SARS-CoV-2 follow-up program.

OUTCOME MEASURES

Abnormal neurologic exams or ASQ scores near or below suggested cut-offs.

RESULTS

Infants received up to three evaluations. Most (28/34; 82 %) were exposed in utero - 16 to symptomatic mothers (IU-S) and 12 to asymptomatic mothers (IU-A). Six were exposed only as a neonate. IU-S had abnormal neurologic exams at mean (SD) age 112 (24) days and ASQ scores near or below cut-offs for all domains more frequently than IU-A or neonatally exposed infants. IU-S were more likely to score below any ASQ cutoff compared to IU-A (P = .04); differences were significant for Fine Motor (P = .01) and Personal-Social (P = .02) domains.

CONCLUSIONS

Early SARS-CoV-2 exposure may impact neurodevelopment, especially among infants exposed in utero to symptomatic gestational parents. Vaccination and other precautions to reduce early-in-life infection may protect against neurodevelopmental delays. Children with early SARS-CoV-2 exposure should have additional longitudinal screening for neurodevelopmental delays.

Placental pathology, neonatal birth weight, and Apgar score in acute and distant SARS-CoV-2 infection

BACKGROUND

Most research on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during pregnancy has been on acute infections with limited data on the effect of distant infection.

AIM

We examined placental pathology and neonatal outcomes in distant SARS-CoV-2 infection earlier in pregnancy compared to acute infections late in pregnancy/at birth and to non-SARS-CoV-2 infected patients with other placental pathologies/clinical presentations.

METHODS

Placentas birthed to unvaccinated patients with SARS-CoV-2 reverse transcription-polymerase chain reaction (RT-PCR) testing and serology testing results from time of delivery were included in this study. A total of 514 singleton placentas between April 18, 2020, and July 26, 2021, were included: 77 acute SARS-CoV-2 infection (RT-PCR positive and serology negative); 222 distant SARS-CoV-2 infection (RT-PCR negative but serology IgG-positive); and 215 non-SARS-Cov-2 infected (RT-PCR negative, serology negative, and history negative) with other placental pathologies: preeclampsia/hypertension, intrauterine growth restriction (IUGR), diabetes, chorioamnionitis, and meconium. Placental pathology findings, Apgar scores, and neonatal birth weights were compared.

RESULTS

Placentas from the acute group had significantly more villous agglutination (10.4%, P = 0.015) and eosinophilic T-cell vasculitis (5.2%, P = 0.004) compared to placentas from the distant group (2.7% and 0%) and non-SARS-CoV-2 placentas (1.9% and 0.9%). One acute case showed SARS-CoV-2 placentitis and resulted in preterm delivery at 25 weeks. Both the preeclampsia/hypertension and the IUGR groups showed significantly more maternal vascular malperfusion findings compared to the acute (6.5%, 6.5% and 1.3%) and distant (7.7%, 7.7%, and 3.2%) groups. Fetal vascular malperfusion findings such as thrombosis of fetal vessels (17.4% P = 0.042) and intramural fibrin deposition (21.7% P = 0.026) were significantly higher in the IUGR group compared to acute (7.8%; 2.6%) and distant (3.6%; 8.1%) infection. Many neonates born to patients infected with SARS-CoV-2 had birth weights outside of 95% confidence range of observed birth weights. There was no association of Apgar scores with infection status or placental pathology.

CONCLUSION

Acute and distant SARS-CoV-2 infections present differing placental pathology.

RELEVANCE FOR PATIENTS

SARS-CoV-2 infection during pregnancy has demonstrable effects on the placenta with potential significant impacts for maternal and fetal health. Prevention of maternal SARS-CoV-2 infection, primarily through vaccination, remains the best mitigation strategy to prevent sequelae of maternal SARS-CoV-2 infection.

Multi-decade national cohort identifies adverse pregnancy and birth outcomes associated with acute respiratory illness hospitalisations during the influenza season

BACKGROUND

Despite the World Health Organization (WHO) recommendation that pregnant women be prioritised for seasonal influenza vaccination, coverage in the Western Pacific Region remains low. Our goal was to provide additional data for the Western Pacific Region about the value of maternal influenza vaccination to pregnant women and their families.

METHODS

We conducted a 16-year retrospective cohort to evaluate risks associated with influenza-associated maternal acute respiratory infection (ARI) in New Zealand. ARI hospitalisations during the May to September influenza season were identified using select ICD-10-AM primary and secondary discharge codes from chapter J00-J99 (diseases of the respiratory system). Cox proportional hazards models were used to calculate crude and adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs).

RESULTS

We identified 822,391 pregnancies among New Zealand residents between 2003 and 2018; 5095 (0.6%) had ≥1 associated ARI hospitalisation during the influenza season; these pregnancies were at greater risk of preterm birth (aHR 1.50, 95% CI 1.39-1.61) and low birthweight (aHR 1.64, 95% CI 1.51-1.79) than pregnancies without such hospitalisations. We did not find an association between maternal ARI hospitalisation and fetal death (aHR 0.96, 95% CI 0.69-1.34) during the influenza season. Maternal influenza vaccination was associated with reduced risk of preterm birth (aHR 0.79, 95% CI 0.77-0.82), low birthweight (aHR 0.87, 95% CI 0.83-0.90) and fetal death (aHR 0.50%, 95% CI 0.44-0.57).

CONCLUSION

In this population-based cohort, being hospitalised for an ARI during the influenza season while pregnant was a risk factor for delivering a preterm or a low birthweight infant and vaccination reduced this risk.

Timing and severity of COVID-19 during pregnancy and risk of preterm birth in the International Registry of Coronavirus Exposure in Pregnancy

Background

Studies of preterm delivery after COVID-19 are often subject to selection bias and do not distinguish between early vs. late infection in pregnancy, nor between spontaneous vs. medically indicated preterm delivery. This study aimed to estimate the risk of preterm birth (overall, spontaneous, and indicated) after COVID-19 during pregnancy, while considering different levels of disease severity and timing.

Methods

Pregnant and recently pregnant people who were tested for or clinically diagnosed with COVID-19 during pregnancy enrolled in an international internet-based cohort study between June 2020 and July 2021. We used several analytic approaches to minimize confounding and immortal time bias, including multivariable regression, time-to-delivery models, and a case-time-control design.

Results

Among 14,264 eligible participants from 70 countries who did not report a pregnancy loss before 20 gestational weeks, 5893 had completed their pregnancies and reported delivery information; others were censored at time of their last follow-up. Participants with symptomatic COVID-19 before 20 weeks’ gestation had no increased risk of preterm delivery compared to those testing negative, with adjusted risks of 10.0% (95% CI 7.8, 12.0) vs. 9.8% (9.1, 10.5). Mild COVID-19 later in pregnancy was not clearly associated with preterm delivery. In contrast, severe COVID-19 after 20 weeks’ gestation led to an increase in preterm delivery compared to milder disease. For example, the risk ratio for preterm delivery comparing severe to mild/moderate COVID-19 at 35 weeks was 2.8 (2.0, 4.0); corresponding risk ratios for indicated and spontaneous preterm delivery were 3.7 (2.0, 7.0) and 2.3 (1.2, 3.9), respectively.

Conclusions

Severe COVID-19 late in pregnancy sharply increased the risk of preterm delivery compared to no COVID-19. This elevated risk was primarily due to an increase in medically indicated preterm deliveries, included preterm cesarean sections, although an increase in spontaneous preterm delivery was also observed. In contrast, mild or moderate COVID-19 conferred minimal risk, as did severe disease early in pregnancy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-022-05101-3.

Maternal immune protection against infectious diseases

The maternal immune system protects developing offspring against pathogens before birth via transplacental transfer and after birth through secreted milk. This transferred maternal immunity influences each generation's susceptibility to infections and responsiveness to immunization. Thus, boosting immunity in the maternal-neonatal dyad is a potentially valuable public health strategy. Additionally, at critical times during fetal and postnatal development, environmental factors and immune stimuli influence immune development. These "windows of opportunity" offer a chance to identify both risk and protective factors that promote long-term health and limit disease. Here, we review pre- and postpartum maternal immune factors that protect against infectious agents in offspring and how they may shape the infant's immune landscape over time. Additionally, we discuss the influence of maternal immunity on the responsiveness to immunization in early life. Lastly, when maternal factors are insufficient to prevent neonatal infectious diseases, we discuss pre- and postnatal therapeutic strategies for the maternal-neonatal dyad.

Bovine Animal Model for Studying the Maternal Microbiome, in utero Microbial Colonization and Their Role in Offspring Development and Fetal Programming

Recent developments call for further research on the timing and mechanisms involved in the initial colonization of the fetal/infant gut by the maternal microbiome and its role in Developmental Origins of Health and Disease (DOHaD). Although progress has been made using primarily preterm infants, ethical and legal constraints hinder research progress in embryo/fetal-related research and understanding the developmental and mechanistic roles of the maternal microbiome in fetal microbial imprinting and its long-term role in early-life microbiome development. Rodent models have proven very good for studying the role of the maternal microbiome in fetal programming. However, some inherent limitations in these animal models make it challenging to study perinatal microbial colonization from a biomedical standpoint. In this review, we discuss the potential use of bovine animals as a biomedical model to study the maternal microbiome, in utero microbial colonization of the fetal gut, and their impact on offspring development and DOHaD.

Dissecting Fc signatures of protection in neonates following maternal influenza vaccination in a placebo-controlled trial

Influenza is an important cause of illness and morbidity for infants. Seasonal influenza vaccination during pregnancy aims to provide protection to mothers, but it can also provide immunity to infants. The precise influence of maternal vaccination on immunity in infants and how vaccine-elicited antibodies provide protection in some but not all infants is incompletely understood. We comprehensively profiled the transfer of functional antibodies and defined humoral factors contributing to immunity against influenza in a clinical trial of maternal influenza vaccination. Influenza-specific antibody subclass levels, Fc ɣ receptor (FCGR) binding levels, and antibody-dependent innate immune functions were all profiled in the mothers during pregnancy and at birth, as well as in cord blood. Vaccination increased influenza-specific antibody levels, antibody binding to FCGR, and specific antibody-dependent innate immune functions in both maternal and cord blood, with FCGR binding most enhanced via vaccination. Influenza-specific FCGR binding levels were lower in cord blood of infants who subsequently developed influenza infection. Collectively these data suggest that in addition to increased antibody amounts, the selective transfer of FCGR-binding antibodies contributes to the protective immune response in infants against influenza.

Prevalence of and factors associated with receipt of provider recommendation for influenza vaccination and uptake of influenza vaccination during pregnancy: cross-sectional study

BACKGROUND

Seasonal influenza vaccination has been recommended for pregnant women in Germany since 2010. The aim of this study was to examine prevalence and determinants of receipt of provider recommendation for influenza vaccination as well as influenza vaccination uptake during pregnancy.

METHODS

We analysed data from the "KUNO Kids Health Study", a prospective birth cohort. During the study period (5th July 2015 to 27th June 2018) data were collected from participating mothers by interview and questionnaire. According to Andersen's behavioural model of health services use potential influencing factors describing the circumstances and characteristics of the mothers and their pregnancies which are potentially affecting whether women receive a recommendation for a vaccination or whether they utilize influenza vaccination were classified into three domains: 'predisposing characteristics', 'enabling resources' and 'need'. Using multivariable logistic regression models odds ratios (OR) and corresponding 95% confidence intervals (95% CI) were calculated.

RESULTS

As a combined result across three flu seasons, 368 of 1814 (20.3%) women received an influenza vaccination recommendation during pregnancy. Having had a high-risk pregnancy increased the odds of receiving a vaccination recommendation (OR = 1.3; 95% CI = 1.0-1.6; p = 0.045). In contrast, pregnancy onset in summer (OR = 0.7; 95% CI = 0.5-1.0; p = 0.027), autumn (OR = 0.4; 95% CI = 0.3-0.5; p < =0.001) or winter (OR = 0.5; 95% CI = 0.3-0.6; p < =0.001) (compared to spring) as well as mother's birthplace outside Germany (OR = 0.6; 95% CI = 0.4-0.9; p = 0.023) reduced the chance of getting a vaccination recommendation. Two hundred forty-two of one thousand eight hundred sixty-five (13%) women were vaccinated against influenza during pregnancy. Having received a vaccination recommendation was strongly associated with vaccination uptake (OR = 37.8; 95% CI = 25.5-55.9; p < =0.001). Higher health literacy status was also associated with a higher chance of vaccination uptake (OR = 1.7; 95% CI = 1.2-2.6; p = 0.008), whereas pregnancy onset in autumn (compared to spring) reduced the chance (OR = 0.5; 95% CI = 0.3-0.8; p = 0.008).

CONCLUSIONS

At 13% the uptake rate of influenza vaccination is low. Having received a recommendation to vaccinate was strongly associated with uptake but only one fifth of all mothers report such a recommendation. Raising awareness in physicians regarding vaccinating during pregnancy seems to be of essential importance to increase vaccine uptake and to prevent influenza-related complications in pregnant women.

Safety, Immunogenicity, Efficacy and Effectiveness of Inactivated Influenza Vaccines in Healthy Pregnant Women and Children Under 5 Years: An Evidence-Based Clinical Review

Annual influenza vaccination is often recommended for pregnant women and young children to reduce the risk of severe influenza. However, most studies investigating the safety, immunogenicity, and efficacy or effectiveness of influenza vaccines are conducted in healthy adults. In this evidence-based clinical review, we provide an update on the safety profile, immunogenicity, and efficacy/effectiveness of inactivated influenza vaccines (IIVs) in healthy pregnant women and children <5 years old. Six electronic databases were searched until May 27, 2021. We identified 3,731 articles, of which 93 met the eligibility criteria and were included. The IIVs were generally well tolerated in pregnant women and young children, with low frequencies of adverse events following IIV administration; however, continuous vaccine safety monitoring systems are necessary to detect rare adverse events. IIVs generated good antibody responses, and the seroprotection rates after IIVs were moderate to high in pregnant women (range = 65%-96%) and young children (range = 50%-100%), varying between the different influenza types/subtypes and seasons. Studies show vaccine efficacy/effectiveness values of 50%-70% in pregnant women and 20%-90% in young children against lab-confirmed influenza, although the efficacy/effectiveness depended on the study design, host factors, vaccine type, manufacturing practices, and the antigenic match/mismatch between the influenza vaccine strains and the circulating strains. Current evidence suggests that the benefits of IIVs far outweigh the potential risks and that IIVs should be recommended for pregnant women and young children.

Lessons learned from the A (H1N1) influenza pandemic

Influenza in pregnancy is a common condition that is associated with an increased risk of hospital admission. Women with comorbidities are at a greater risk of severe outcomes. There are substantial gaps in our knowledge of the impact of severe influenza on perinatal outcomes, particularly in low- and middle-income countries, but preterm birth, fetal death, infant respiratory infection and hospital admission may be increased. Thus, influenza is a major burden on health services. Immunisation is cost-effective, safe and effective in preventing influenza in pregnant women and their infants but policies and uptake vary worldwide. Operational challenges and concern over the safety, efficacy and necessity of immunisation are common, and there is a lack of evidence on how to overcome these barriers. This review identifies learning points that are relevant to the current coronavirus disease-2019 pandemic through describing the epidemiology and impact of seasonal and A(H1N1)pdm09 influenza in pregnancy, alongside the effectiveness and use of immunisation.

Incidence rates of influenza illness during pregnancy in Suzhou, China, 2015-2018

Background

Data on influenza incidence during pregnancy in China are limited.

Methods

From October 2015 to September 2018, we conducted active surveillance for acute respiratory illness (ARI) among women during pregnancy. Nurses conducted twice weekly phone and text message follow‐up upon enrollment until delivery to identify new episodes of ARI. Nasal and throat swabs were collected ≤10 days from illness onset to detect influenza.

Results

In total, we enrolled 18 724 pregnant women median aged 28 years old, 37% in first trimester, 48% in second trimester, and 15% in third trimester, with seven self‐reported influenza vaccination during pregnancy. In the 18‐week epidemic period during October 2015 to September 2016, influenza incidence was 0.7/100 person‐months (95% CI: 0.5–0.9). In the cumulative 29‐week‐long epidemic during October 2016 to September 2017, influenza incidence was 1.0/100 person‐months (95% CI: 0.8–1.2). In the 11‐week epidemic period during October 2017 to September 2018, influenza incidence was 2.1/100 person‐months (95% CI: 1.9–2.4). Influenza incidence was similar by trimester. More than half of the total influenza illnesses had no elevated temperature and cough. Most influenza‐associated ARIs were mild, and <5.1% required hospitalization.

Conclusions

Influenza illness in all trimesters of pregnancy was common. These data may help inform decisions regarding the use of influenza vaccine to prevent influenza during pregnancy.

Mycobacterium tuberculosis causes a leaky blood-brain barrier and neuroinflammation in the prefrontal cortex and cerebellum regions of infected mice offspring

The maternal system's exposure to pathogens influences foetal brain development through the influx of maternal cytokines and activation of the foetal immune status to a persistent inflammatory state characterised by glia cell activation. Neuroinflammation influences the blood-brain barrier's (BBB) permeability allowing peripheral immune cell trafficking into the brain. Mycobacterium tuberculosis (Mtb) is a pathogen that causes Tuberculosis (TB), a global pandemic responsible for health and economic burdens. Although it is known that maternal infections increase the risk of Autism spectrum disorder (ASD), it is not known whether gestational Mtb infections also contribute to impaired foetal neurodevelopment. Here we infect pregnant Balb/c mice with Mtb H37Rv and Valproic acid (VPA) individually and in combination. Neuroinflammation was measured by assessing microglia and astrocyte population in the prefrontal cortex (PFC) and cerebellum (CER) of pups. Mtb infection increased the microglia population and caused morphological changes to a reactive phenotype in the PFC. Also, the astrocyte population was significantly increased in the PFC of Mtb pups. The BBB permeability was determined by measuring the Evans Blue (EB) dye concentration in the PFC and CER 1 hr post receiving intravenous EB-dye injection. We found that prenatal Mtb exposure significantly increased the BBB's permeability in the PFC and CER of pups versus saline. Overall, our data demonstrate that prenatal exposure to Mtb predisposes offspring to a higher risk of BBB damage while inducing persistent neuroinflammation, which could lead to impaired neuronal development and function. These findings implicate a potential role of gestational Mtb infections in the aetiology of ASD.

Clinical Effectiveness and Safety of Antivirals for Influenza in Pregnancy

Seasonal influenza epidemics result in substantial health care burden annually. Early initiation of antiviral treatment of influenza has been shown to reduce the risk of complications and duration of illness. Pregnant and postpartum women may be at increased risk for influenza-associated complications; however, pregnant women have been generally excluded from clinical trials of antiviral treatment of influenza. In this review, we summarize the available evidence on the clinical effectiveness and safety of antiviral treatment of pregnant women with influenza. Observational data show a reduction of severe outcomes when pregnant and postpartum women are treated with oseltamivir and other neuraminidase inhibitors without increased risk of adverse maternal, fetal, or neonatal outcomes. Due to lack of safety and efficacy data for baloxavir treatment of pregnant and postpartum women, baloxavir is currently not recommended for use in these populations.

Cost-effectiveness of influenza vaccination during pregnancy

OBJECTIVE

To assess the cost-effectiveness of influenza vaccination for all pregnant patients in the United States.

METHODS

We designed a cost-effectiveness model to compare outcomes and costs in pregnant patients who received the inactivated, trivalent influenza vaccine to those who did not. We used a theoretical cohort of 4 million patients, the number of individuals giving birth in the United States per year. We assumed that H1N1 and A or B type influenza were of equal incidence based on seasonal variation from the past ten years. Our outcomes include acquiring H1N1, acquiring A or B type influenza, maternal death, stillbirth, infant death, preterm birth, and cerebral palsy in addition to cost and quality-adjusted life years (QALYs). Probabilities were derived from the literature and QALYs generated at a discount rate of 3%. Sensitivity analyses were performed to assess the robustness of our model.

RESULTS

In our theoretical cohort of 4 million pregnant patients, the influenza vaccination strategy was associated with 1632 fewer stillbirths (24,332 in the vaccine strategy vs. 25,964 in the no vaccine strategy), 120 fewer maternal deaths (284 vs. 404), 340 fewer infant deaths (5608 vs. 5948), 32,856 fewer preterm births (403,896 vs. 436,752), and 641 fewer cases of moderate cerebral palsy (12,388 vs. 13,029). Additionally, the vaccination strategy corresponded to savings of $3.7 billion ($63.3 billion vs. $67.0 billion) and increased QALYs of 81,696 (226,852,076 vs 226,770,380). Therefore, it was considered a dominant strategy. Univariate sensitivity analysis demonstrated that the vaccine is cost saving until vaccine cost passes $900, far above the current cost of $12.16. In addition, we used sensitivity analysis to vary seasonal proportions of H1N1 to A or B type influenza. The vaccine was cost saving and increased QALYs for any proportion of H1N1 to A or B type influenza including when H1N1 was absent.

CONCLUSION

We demonstrate that in a cohort of 4 million patients, the influenza vaccine may save $3.7 billion per year, improve maternal and infant outcomes, and reduce morbidity and mortality. Our study provides further evidence that providers should strongly recommend that pregnant patients receive their annual influenza vaccine.

Outcomes of Maternal-Newborn Dyads After Maternal SARS-CoV-2

BACKGROUND AND OBJECTIVES

Infection with a novel coronavirus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a global pandemic. There are limited data describing the impact of SARS-CoV-2 infection on pregnant mothers and their newborns. The objective of this study is to describe characteristics and outcomes of maternal-newborn dyads with confirmed maternal SARS-CoV-2.

METHODS

This was a multicenter, observational, descriptive cohort study with data collection from charts of maternal-newborn dyads who delivered at 4 major New York City metropolitan area hospitals between March 1 and May 10, 2020, with maternal SARS-CoV-2 infection.

RESULTS

There were a total of 149 mothers with SARS-CoV-2 infection and 149 newborns analyzed (3 sets of twins; 3 stillbirths). Forty percent of these mothers were asymptomatic. Approximately 15% of symptomatic mothers required some form of respiratory support, and 8% required intubation. Eighteen newborns (12%) were admitted to the ICU. Fifteen (10%) were born preterm, and 5 (3%) required mechanical ventilation. Symptomatic mothers had more premature deliveries (16% vs 3%, P = .02), and their newborns were more likely to require intensive care (19% vs 2%, P = .001) than asymptomatic mothers. One newborn tested positive for SARS-CoV-2, which was considered a case of horizontal postnatal transmission.

CONCLUSIONS

Although there was no distinct evidence of vertical transmission from mothers with SARS-CoV-2 to their newborns, we did observe perinatal morbidities among both mothers and newborns. Symptomatic mothers were more likely to experience premature delivery and their newborns to require intensive care.

Maternal Influenza A Virus Infection Restricts Fetal and Placental Growth and Adversely Affects the Fetal Thymic Transcriptome

Maternal influenza A viral infections in humans are associated with low birth weight, increased risk of pre-term birth, stillbirth and congenital defects. To examine the effect of maternal influenza virus infection on placental and fetal growth, pregnant C57BL/6 mice were inoculated intranasally with influenza A virus A/CA/07/2009 pandemic H1N1 or phosphate-buffered saline (PBS) at E3.5, E7.5 or E12.5, and the placentae and fetuses collected and weighed at E18.5. Fetal thymuses were pooled from each litter. Placentae were examined histologically, stained by immunohistochemistry (IHC) for CD34 (hematopoietic progenitor cell antigen) and vascular channels quantified. RNA from E7.5 and E12.5 placentae and E7.5 fetal thymuses was subjected to RNA sequencing and pathway analysis. Placental weights were decreased in litters inoculated with influenza at E3.5 and E7.5. Placentae from E7.5 and E12.5 inoculated litters exhibited decreased labyrinth development and the transmembrane protein 150A gene was upregulated in E7.5 placentae. Fetal weights were decreased in litters inoculated at E7.5 and E12.5 compared to controls. RNA sequencing of E7.5 thymuses indicated that 957 genes were downregulated ≥2-fold including Mal, which is associated with Toll-like receptor signaling and T cell differentiation. There were 28 upregulated genes. It is concluded that maternal influenza A virus infection impairs fetal thymic gene expression as well as restricting placental and fetal growth.

Paradoxical long-term impact of maternal influenza infection on neonates and infants

Background

Pregnant women are at high risk of influenza-related morbidity and mortality. In addition, maternal influenza infection may lead to adverse birth outcomes. However, there is insufficient data on long-term impact of maternal influenza infection.

Methods

This study was conducted to assess the impact of maternal influenza infection on birth outcomes and long-term influence on infants by merging the Korea National Health Insurance (KNHI) claims database and National Health Screening Program for Infants and Children (NHSP-IC). Mother-offspring pairs were categorized by maternal influenza infection based on the ICD-10 code.

Results

Multivariate analysis revealed that maternal influenza infection significantly increased the risk of preterm birth (OR 1.408) and low birth weight (OR 1.198) irrespective of gestational age. The proportion of low birth weight neonates was significantly higher in influenza-infected women compared to those without influenza. However, since the fourth health screening (30–80 months after birth), the fraction of underweight was no longer different between children from influenza-infected and non-infected mothers, whereas the rates of overweight increased paradoxically in those born to mothers with influenza infection.

Conclusions

Maternal influenza infection might have long-term effects on the health of children and adolescents even after infancy.

Environmental complex exposure and the risk of influenza-like illness among housewives: A case study in Shanxi Province, China

The association between environmental pollution and risk of influenza-like illness (ILI) among general population has been reported. However, the relationships between the individual pollutants and ILI risk are still under discussion. Our study aimed to explore the associations of the typical environmental polycyclic aromatic hydrocarbons (PAHs) and metal(loid)s with ILI risk among women population. We carried out a cross-sectional study and included a total of 396 housewives in Shanxi Province, China. The information on their general characteristics and ILI frequency was collected by questionnaire. We collected their hair samples and analyzed the concentrations of PAHs and various metal(loid)s. The results indicated that only acenaphthylene concentration of the nine detected PAH congeners in the hair was significantly associated with ILI risk with adjusted odds ratio (AOR) and 95% confidence interval (95% CI) of 0.58 (0.38 - 0.91). Among the concerned 4 toxic metal(loid)s and 15 rare earth elements, only the hair concentration of arsenic had a positive dose-response relationship with ILI risk. In addition, we found that there were negative dose-response associations of the three essential trace elements (i.e. chromium, cobalt, and nickel), and four essential alkaline earth elements (i.e. magnesium, calcium, strontium, barium) with ILI risk. It was concluded that the environmental exposure to certain compounds of housewives may contribute to their ILI development.

An international cohort study of birth outcomes associated with hospitalized acute respiratory infection during pregnancy

OBJECTIVES

Findings during the 2009 pandemic suggest severe maternal infection with pandemic influenza had adverse perinatal health consequences. Limited data exist evaluating the perinatal health effects of severe seasonal influenza and non-influenza infections during pregnancy.

METHODS

A retrospective cohort of pregnant women from Australia, Canada, Israel, and the United States was established using birth records to identify pregnancies and birth outcomes and hospital and laboratory testing records to identify influenza and non-influenza associated acute respiratory or febrile illness (ARFI) hospitalizations. ARFI hospitalized women were matched to non-hospitalized women (1:4) by country and season of conception. Log-binomial regression was used to estimate the relative risk (aRR) of preterm birth (PTB), small-for-gestational-age (SGA), and low birthweight (LBW) birth, adjusting for pre-existing medical conditions, maternal age, and parity.

RESULTS

950 pregnant women hospitalized with an ARFI were matched with 3,800 non-hospitalized pregnant women. Compared to non-hospitalized women, risk of PTB was greater among women hospitalized with influenza-associated ARFI (aRR: 1.57; 95% CI: 1.15-2.15) and non-influenza ARFI (aRR: 2.78; 95% CI: 2.12-3.65). Similar results were observed for LBW; there were no associations with SGA birth.

CONCLUSIONS

ARFI hospitalization during pregnancy was associated with increased risk of PTB and LBW.

Review of the status and challenges associated with increasing influenza vaccination coverage among pregnant women in China

Influenza vaccination coverage in pregnant women in China remains low. In this review, we first provide an overview of the evidence for the use of influenza vaccination during pregnancy. Second, we discuss influenza vaccination policy and barriers to increased seasonal influenza vaccination coverage in pregnant women in China. Third, we provide case studies of successes and challenges of programs for increasing seasonal influenza vaccination in pregnant women from other parts of Asia with lessons learned for China. Finally, we assess opportunities and challenges for increasing influenza vaccination coverage among pregnant women in China.

Influenza-Associated Outcomes Among Pregnant, Postpartum, and Nonpregnant Women of Reproductive Age

BACKGROUND

Pregnant women are prioritized for seasonal influenza vaccination, but the evidence on the risk of influenza during pregnancy that is used to inform these policies is limited.

METHODS

Individual-level administrative data sets and active surveillance data were joined to estimate influenza-associated hospitalization and outpatient visit rates by pregnancy, postpartum, and trimester status.

RESULTS

During 2012-2015, 46 of 260 (17.7%) influenza-confirmed hospitalizations for acute respiratory infection and 13 of 294 (4.4%) influenza-confirmed outpatient visits were among pregnant and postpartum women. Pregnant and postpartum women experienced higher rates of influenza-associated hospitalization than nonpregnant women overall (rate ratio [RR], 3.4; 95% confidence interval [CI], 2.5-4.7) and by trimester (first, 2.5 [95% CI, 1.2-5.4]; second, 3.9 [95% CI, 2.4-6.3]; and third, 4.8 [95% CI, 3.0-7.7]); the RR for the postpartum period was 0.7 (95% CI, 3.0-7.7). Influenza A viruses were associated with an increased risk (RR for 2009 pandemic influenza A[H1N1] virus, 5.3 [95% CI, 3.2-8.7]; RR for influenza A(H3N2) virus, 3.0 [95% CI, 1.8-5.0]), but influenza B virus was not (RR, 1.8; 95% CI, .7-4.6). Influenza-associated hospitalization rates in pregnancy were significantly higher for Māori women (RR, 3.2; 95% CI, 1.3-8.4), compared with women of European or other ethnicity. Similar risks for influenza-confirmed outpatient visits were not observed.

CONCLUSION

Seasonal influenza poses higher risks of hospitalization among pregnant women in all trimesters, compared with nonpregnant women. Hospitalization rates vary by influenza virus type and ethnicity among pregnant women.

Seasonal and pandemic influenza during pregnancy and risk of fetal death: A Norwegian registry-based cohort study

Previous studies of fetal death with maternal influenza have been inconsistent. We explored the effect of maternal influenza-like illness (ILI) in pregnancy on the risk of fetal death, distinguishing between diagnoses during regular influenza seasons and the 2009/2010 pandemic and between trimesters of ILI. We used birth records from the Medical Birth Registry of Norway to identify fetal deaths after the first trimester in singleton pregnancies (2006-2013). The Norwegian Directorate of Health provided dates of clinical influenza diagnoses by primary-health-care providers, whereas dates of laboratory-confirmed influenza A (H1N1) diagnoses were provided by the Norwegian Surveillance System for Communicable Diseases. We obtained dates and types of influenza vaccinations from the Norwegian Immunisation Registry. Cox proportional-hazards regression models were fitted to estimate hazard ratios (HRs) of fetal death, with associated 95% confidence intervals (CIs), comparing women with and without an ILI diagnosis in pregnancy. There were 2510 fetal deaths among 417,406 eligible pregnancies. ILI during regular seasons was not associated with increased risk of fetal death: adjusted HR = 0.90 (95% CI 0.64-1.27). In contrast, ILI during the pandemic was associated with substantially increased risk of fetal death, with an adjusted HR of 1.75 (95% CI 1.21-2.54). The risk was highest following first-trimester ILI (adjusted HR = 2.28 [95% CI 1.45-3.59]). ILI during the pandemic-but not during regular seasons-was associated with increased risk of fetal death in the second and third trimester. The estimated effect was strongest with ILI in first trimester.

Developing routinely recorded clinical data from electronic patient records as a national resource to improve neonatal health care: the Medicines for Neonates research programme

Background

Clinical data offer the potential to advance patient care. Neonatal specialised care is a high-cost NHS service received by approximately 80,000 newborn infants each year.

Objectives

(1) To develop the use of routinely recorded operational clinical data from electronic patient records (EPRs), secure national coverage, evaluate and improve the quality of clinical data, and develop their use as a national resource to improve neonatal health care and outcomes. To test the hypotheses that (2) clinical and research data are of comparable quality, (3) routine NHS clinical assessment at the age of 2 years reliably identifies children with neurodevelopmental impairment and (4) trial-based economic evaluations of neonatal interventions can be reliably conducted using clinical data. (5) To test methods to link NHS data sets and (6) to evaluate parent views of personal data in research.

Design

Six inter-related workstreams; quarterly extractions of predefined data from neonatal EPRs; and approvals from the National Research Ethics Service, Health Research Authority Confidentiality Advisory Group, Caldicott Guardians and lead neonatal clinicians of participating NHS trusts.

Setting

NHS neonatal units.

Participants

Neonatal clinical teams; parents of babies admitted to NHS neonatal units.

Interventions

In workstream 3, we employed the Bayley-III scales to evaluate neurodevelopmental status and the Quantitative Checklist of Autism in Toddlers (Q-CHAT) to evaluate social communication skills. In workstream 6, we recruited parents with previous experience of a child in neonatal care to assist in the design of a questionnaire directed at the parents of infants admitted to neonatal units.

Data sources

Data were extracted from the EPR of admissions to NHS neonatal units.

Main outcome measures

We created a National Neonatal Research Database (NNRD) containing a defined extract from real-time, point-of-care, clinician-entered EPRs from all NHS neonatal units in England, Wales and Scotland (n = 200), established a UK Neonatal Collaborative of all NHS trusts providing neonatal specialised care, and created a new NHS information standard: the Neonatal Data Set (ISB 1595) (see http://webarchive.nationalarchives.gov.uk/±/http://www.isb.nhs.uk/documents/isb-1595/amd-32–2012/index_html; accessed 25 June 2018).

Results

We found low discordance between clinical (NNRD) and research data for most important infant and maternal characteristics, and higher prevalence of clinical outcomes. Compared with research assessments, NHS clinical assessment at the age of 2 years has lower sensitivity but higher specificity for identifying children with neurodevelopmental impairment. Completeness and quality are higher for clinical than for administrative NHS data; linkage is feasible and substantially enhances data quality and scope. The majority of hospital resource inputs for economic evaluations of neonatal interventions can be extracted reliably from the NNRD. In general, there is strong parent support for sharing routine clinical data for research purposes.

Limitations

We were only able to include data from all English neonatal units from 2012 onwards and conduct only limited cross validation of NNRD data directly against data in paper case notes. We were unable to conduct qualitative analyses of parent perspectives. We were also only able to assess the utility of trial-based economic evaluations of neonatal interventions using a single trial. We suggest that results should be validated against other trials.

Conclusions

We show that it is possible to obtain research-standard data from neonatal EPRs, and achieve complete population coverage, but we highlight the importance of implementing systematic examination of NHS data quality and completeness and testing methods to improve these measures. Currently available EPR data do not enable ascertainment of neurodevelopmental outcomes reliably in very preterm infants. Measures to maintain high quality and completeness of clinical and administrative data are important health service goals. As parent support for sharing clinical data for research is underpinned by strong altruistic motivation, improving wider public understanding of benefits may enhance informed decision-making.

Future work

We aim to implement a new paradigm for newborn health care in which continuous incremental improvement is achieved efficiently and cost-effectively by close integration of evidence generation with clinical care through the use of high-quality EPR data. In future work, we aim to automate completeness and quality checks and make recording processes more ‘user friendly’ and constructed in ways that minimise the likelihood of missing or erroneous entries. The development of criteria that provide assurance that data conform to prespecified completeness and quality criteria would be an important development. The benefits of EPR data might be extended by testing their use in large pragmatic clinical trials. It would also be of value to develop methods to quality assure EPR data including involving parents, and link the NNRD to other health, social care and educational data sets to facilitate the acquisition of lifelong outcomes across multiple domains.

Study registration

This study is registered as PROSPERO CRD42015017439 (workstream 1) and PROSPERO CRD42012002168 (workstream 3).

Funding

The National Institute for Health Research Programme Grants for Applied Research programme (£1,641,471). Unrestricted donations were supplied by Abbott Laboratories (Maidenhead, UK: £35,000), Nutricia Research Foundation (Schiphol, the Netherlands: £15,000), GE Healthcare (Amersham, UK: £1000). A grant to support the use of routinely collected, standardised, electronic clinical data for audit, management and multidisciplinary feedback in neonatal medicine was received from the Department of Health and Social Care (£135,494).

Dengue during pregnancy and live birth outcomes: a cohort of linked data from Brazil

OBJECTIVES

Dengue is the most common viral mosquito-borne disease, and women of reproductive age who live in or travel to endemic areas are at risk. Little is known about the effects of dengue during pregnancy on birth outcomes. The objective of this study is to examine the effect of maternal dengue severity on live birth outcomes.

DESIGN AND SETTING

We conducted a population-based cohort study using routinely collected Brazilian data from 2006 to 2012.

PARTICIPATING

We linked birth registration records and dengue registration records to identify women with and without dengue during pregnancy. Using multinomial logistic regression and Firth method, we estimated risk and ORs for preterm birth (<37 weeks' gestation), low birth weight (<2500 g) and small for gestational age (<10thcentile). We also investigated the effect of time between the onset of the disease and each outcome.

RESULTS

We included 16 738 000 live births. Dengue haemorrhagic fever was associated with preterm birth (OR=2.4; 95% CI 1.3 to 4.4) and low birth weight (OR=2.1; 95% CI 1.1 to 4.0), but there was no evidence of effect for small for gestational age (OR=2.1; 95% CI 0.4 to 12.2). The magnitude of the effects was higher in the acute disease period.

CONCLUSION

This study showed an increased risk of adverse birth outcomes in women with severe dengue during pregnancy. Medical intervention to mitigate maternal risk during severe acute dengue episodes may improve outcomes for infants born to exposed mothers.

Social Networks and the Emergence of Health Inequalities Following a Medical Advance: Examining Prenatal H1N1 Vaccination Decisions

Health inequalities persist, in part, because people in socioeconomically advantageous positions possess resources to avoid new health risks when medicine advances. Although these health decisions rarely occur in isolation, we know less about the specific role of networks. We examine whether social capital mediates the relationship between individual educational attainment and decisions about a medical advance: H1N1 vaccination during pregnancy. Building on prior work that defines social capital as the resources of network members, we examine two mechanisms through which social capital may affect health decisions, facilitating information flow and exerting influence. Using egocentric network data collected from 225 pregnant women during the 2009-10 H1N1 pandemic, we measure social capital as the proportion of networks that are college-educated H1N1 discussants (information flow) and the proportion of college-educated H1N1 supporters (influence). Findings reveal that college-educated women knew more college-educated H1N1 discussants and supporters. Further, both measures of social capital predicted higher probabilities of vaccination, with the latter mechanism emerging as a particularly strong predictor. Our findings provide evidence that health decisions are shaped by individual resources as well as social capital available through network ties, offering a unique perspective of the ways that social networks contribute to producing, and potentially reproducing, unequal health.

Outcomes of infants born to women with influenza A(H1N1)pdm09

BACKGROUND

Pregnant women with influenza are more likely to have complications, but information on infant outcomes is limited.

METHODS

Five state/local health departments collected data on outcomes of infants born to pregnant women with 2009 H1N1 influenza reported to the Centers for Disease Control and Prevention from April to December 2009. Collaborating sites linked information on pregnant women with confirmed 2009 H1N1 influenza, many who were severely ill, to their infants' birth certificates. Collaborators also collected birth certificate data from two comparison groups that were matched with H1N1-affected pregnancies on month of conception, sex, and county of residence.

RESULTS

490 pregnant women with influenza, 1,451 women without reported influenza with pregnancies in the same year, and 1,446 pregnant women without reported influenza with prior year pregnancies were included. Women with 2009 H1N1 influenza admitted to an intensive care unit (ICU; n = 64) were more likely to deliver preterm infants (<37 weeks), low birth weight infants, and infants with Apgar scores <=6 at 5 min than women in comparison groups (adjusted relative risk, aRR = 3.9 [2.7, 5.6], aRR = 4.6 [2.9, 7.5], and aRR = 8.7 [3.6, 21.2], for same year comparisons, respectively). Women with influenza who were not hospitalized and hospitalized women not admitted to the ICU did not have significantly elevated risks for adverse infant outcomes.

CONCLUSIONS

Severely ill women with 2009 H1N1 influenza during pregnancy were more likely to have adverse birth outcomes than women without influenza, providing more support for influenza vaccination during pregnancy.

Short-Term Birth Sequelae of the 1918-1920 Influenza Pandemic in the United States: State-Level Analysis

This paper examines short-term birth sequelae of the influenza pandemic of 1918-1920 in the United States using monthly data on births and all-cause deaths for 19 US states in conjunction with data on maternal deaths, stillbirths, and premature births. The data on births and all-cause deaths are adjusted for seasonal and trend effects, and the residual components of the 2 time series coinciding with the timing of peak influenza mortality are examined for these sequelae. Notable findings include: 1) a drop in births in the 3 months following peak mortality; 2) a reversion in births to normal levels occurring 5-7 months after peak mortality; and 3) a steep drop in births occurring 9-10 months after peak mortality. Interpreted in the context of parallel data showing elevated premature births, stillbirths, and maternal mortality during times of peak influenza mortality, these findings suggest that the main impacts of the 1918-1920 influenza on reproduction occurred through: 1) impaired conceptions, possibly due to effects on fertility and behavioral changes; 2) an increase in the preterm delivery rate during the peak of the pandemic; and 3) elevated maternal and fetal mortality, resulting in late-term losses in pregnancy.

Risk of pregnancy complications and adverse birth outcomes after maternal A(H1N1)pdm09 influenza: a Norwegian population-based cohort study

Background

The effects of maternal influenza infection on the fetus remain unclear. We studied mild influenza and influenza antibodies in relation to birth weight and risks of pre-eclampsia, preterm birth (PTB), and small for gestational age (SGA) birth among the unvaccinated participants in the Norwegian Influenza Pregnancy Cohort.

Methods

Pregnant women attending a routine ultrasound were recruited from four hospitals in Norway shortly after the 2009 A(H1N1) pandemic. The present study was restricted to unvaccinated participants who were pregnant during the pandemic. Information on the participants was obtained through questionnaires and linkage with national registries. Maternal blood samples were collected at delivery. Women with laboratory-confirmed A(H1N1)pdm09 influenza, a clinical diagnosis of influenza, or self-reported influenza during the pandemic were classified as having had influenza. A(H1N1)pdm09-specific antibodies in serum were detected with the hemagglutination-inhibition assay. Detection of antibodies was considered an indicator of infection during the pandemic in the unvaccinated participants. Odds ratios were estimated with logistic regression. Quantile regression was used to estimate differences in the distribution of birth weight.

Results

Among the 1258 women included in this study, there were 37 cases of pre-eclampsia, 41 births were PTB, and 103 births were SGA. 226 women (18.0%) had influenza during the pandemic. The majority of cases did not receive medical care, and only a small proportion (1.3%) of the cases were hospitalized. Thus, the cases consisted primarily of women with mild illness. No significant associations between influenza and risk of pre-eclampsia, PTB, or SGA birth were observed. Detection of A(H1N1)pdm09-specific antibodies was associated with a lower 10th percentile of birth weight, β = − 159 g (95% CI − 309, − 9).

Conclusions

Mild influenza illness during pregnancy was not associated with increased risk of pre-eclampsia, PTB or SGA birth. However, influenza infection during pregnancy may reduce the birth weight of the smallest children.

The Relationship Between 2009 Pandemic H1N1 Influenza During Pregnancy and Preterm Birth: A Population-based Cohort Study

BACKGROUND

Previous studies of maternal influenza illness and preterm birth have yielded inconsistent results. Our objective was to assess the association between 2009 pandemic H1N1 (pH1N1) influenza during pregnancy and preterm birth in a large obstetrical population.

METHODS

We linked a province-wide birth registry with health administrative databases to identify influenza-coded hospitalizations, emergency department visits, or physician visits among pregnant women during the 2009 H1N1 pandemic (our proxy for clinical pH1N1 influenza illness). Using Cox regression, we estimated adjusted hazard ratios (aHR) for preterm birth and spontaneous preterm birth treating influenza as a time-varying exposure.

RESULTS

Among 192,082 women with a singleton live birth, 2,925 (1.5%) had an influenza-coded health care encounter during the 2009 H1N1 pandemic. Compared with unexposed pregnancy time, there was no association between exposure to the pandemic, with or without clinical influenza illness, and preterm birth (no pH1N1 diagnosis: aHR = 1.0; 95% confidence interval [CI] = 0.98, 1.1; pH1N1 diagnosis: aHR = 1.0; 95% CI = 0.88, 1.2). Among women with preexisting medical conditions, influenza was associated with increased preterm birth (aHR = 1.5; 95% CI = 1.1, 2.2) and spontaneous preterm birth (aHR = 1.7; 95% CI = 1.1, 2.6), and these associations were strongest in the third trimester and when data were analyzed to allow for a transient acute effect of influenza.

CONCLUSIONS

In the general obstetrical population, there was no association between pH1N1 influenza illness and preterm birth, but women with preexisting medical conditions known to increase the risk of influenza-associated morbidity were at elevated risk.

Prenatal inflammation exposure-programmed cardiovascular diseases and potential prevention

In recent years, the rapid development of medical and pharmacological interventions has led to a steady decline in certain noncommunicable chronic diseases (NCDs), such as cancer. However, the overall incidence of cardiovascular diseases (CVDs) has not seemed to decline. CVDs have become even more prevalent in many countries and represent a global health threat and financial burden. An increasing number of epidemiological and experimental studies have demonstrated that maternal insults not only can result in birth defects but also can cause developmental functional defects that contribute to adult NCDs. In the current review, we provide an overview of evidence from both epidemiological investigations and experimental animal studies supporting the concept of developmental reprogramming of adult CVDs in offspring that have experienced prenatal inflammation exposure (PIE) during fetal development (PIE-programmed CVDs), a disease-causing event that has not been effectively controlled. This review describes the epidemiological observations, data from animal models, and related mechanisms for the pathogenesis of PIE-programmed CVDs. In addition, the potential therapeutic interventions of PIE-programmed CVDs are discussed. Finally, we also deliberate the need for future mechanistic studies and biomarker screenings in this important field, which creates a great opportunity to combat the global increase in CVDs by managing the adverse effects of inflammation for prepregnant and pregnant individuals who are at risk for PIE-programmed CVDs.

Propensity Score-Matched Analysis on the Association Between Pregnancy Infections and Adverse Birth Outcomes in Rural Northwestern China

The purpose of this study is to examine the relationship between infections and birth outcomes in pregnant Chinese women by using propensity score (PS) matching. The data used here was from a large population-based cross-sectional epidemiological survey on birth defects in Shaanxi province, Northwest China. The babies born during 2010–2013 and their mothers were selected with a stratified multistage sampling method. We used PS-matched (1:1) analysis to match participants with infections to participants without infections. Of 22916 rural participants, the overall prevalence of infection was about 39.96%. 5381 pairs were matched. We observed increased risks of birth defects with infections, respiratory infections and genitourinary infections during the pregnancy (OR, 1.59; 95% CI: 1.21–2.08; OR, 1.44; 95% CI: 1.10–1.87; OR, 3.11; 95% CI: 1.75–5.54). There was also a significant increase of low birth weight associated with respiratory infections (1.13(1.01–1.27)). The association of birth defect with the infection could be relatively stable but the effect could be mediated by some important factors such as mother’s age, education level and economic level. The infection during pregnancy is common in Chinese women and might increase the risk of offspring birth defects and low birth weight, especially in younger, lower education, poor pregnant women.

Severe influenza A(H1N1)pdm09 in pregnant women and neonatal outcomes, State of Sao Paulo, Brazil, 2009

To investigate the factors associated with death and describe the gestational outcomes in pregnant women with influenza A(H1N1)pdm09, we conducted a case-control study (deaths and recovered) in hospitalized pregnant women with laboratory-confirmed influenza A(H1N1)pdm09 with severe acute respiratory illness (SARI) in the state of São Paulo from June 9 to December 1, 2009. All cases were evaluated, and four controls that were matched by the epidemiological week of hospitalization of the case were randomly selected for each case. Cases and controls were selected from the National Disease Notification System-SINAN Influenza-web. The hospital records from 126 hospitals were evaluated, and home interviews were conducted using standardized forms. A total of 48 cases and 185 controls were investigated. Having had a previous health visit to a healthcare provider for an influenza episode before hospital admission was a risk factor for death (adjusted OR (ORadj) of 7.93, 95% CI 2.19-28.69). Although not significant in the multiple analysis (ORadj of 2.13, 95% CI 0.91-5.00), the 3rd trimester deserves attention, with an OR = 2.22, 95% CI 1.13-4.37 in the univariate analysis. Antiviral treatment was a protective factor when administered within 48 hours of symptom onset (ORadj = 0.16, 95% CI 0.05-0.50) and from 48 to 72 hours (ORadj = 0.09, 95% CI 0.01-0.87). There was a higher proportion of fetal deaths and preterm births among cases (p = 0.001) and live births with low weight (p = 0.019), compared to control subjects who gave birth during hospitalization. After discharge, control subjects had a favorable neonatal outcome. Early antiviral treatment during the presence of a flu-like illness is an important factor in reducing mortality from influenza in pregnant women and unfavorable neonatal outcomes. It is important to monitor pregnant women, particularly in the 3rd trimester of gestation, with influenza illness for diagnosis and early treatment.

Epidemiology of seasonal influenza infection in pregnant women and its impact on birth outcomes

Seasonal influenza can cause significant morbidity in pregnant women. Much of the existing epidemiological evidence on influenza during pregnancy has focused on the 2009 A/H1N1 pandemic. To measure the epidemiological characteristics of seasonal influenza infection among pregnant women and the impact on infant health, a cohort of 86 779 pregnancies during the influenza season (2012-2014) was established using probabilistic linkage of notifiable infectious disease, hospital admission, and birth information. A total of 192 laboratory-confirmed influenza infections were identified (2·2 per 1000 pregnancies), 14·6% of which were admitted to hospital. There was no difference in the proportion of infections admitted to hospital by trimester or subtype of infection. Influenza B infections were more likely to occur in second trimester compared with influenza A/H3N2 and influenza A/H1N1 infections (41·3%, 23·6%, and 33·3%, respectively), and on average, infants born to women with influenza B during pregnancy had 4·0% (95% CI 0·3-7·6%) lower birth weight relative to optimal compared with infants born to uninfected women (P = 0·03). Results from this linked population-based study suggest that there are differences in maternal infection by virus type and subtype and support the provision of seasonal influenza vaccine to pregnant women.

Influenza epidemiology and immunization during pregnancy: Final report of a World Health Organization working group

From 2014 to 2017, the World Health Organization convened a working group to evaluate influenza disease burden and vaccine efficacy to inform estimates of maternal influenza immunization program impact. The group evaluated existing systematic reviews and relevant primary studies, and conducted four new systematic reviews. There was strong evidence that maternal influenza immunization prevented influenza illness in pregnant women and their infants, although data on severe illness prevention were lacking. The limited number of studies reporting influenza incidence in pregnant women and infants under six months had highly variable estimates and underrepresented low- and middle-income countries. The evidence that maternal influenza immunization reduces the risk of adverse birth outcomes was conflicting, and many observational studies were subject to substantial bias. The lack of scientific clarity regarding disease burden or magnitude of vaccine efficacy against severe illness poses challenges for robust estimation of the potential impact of maternal influenza immunization programs.

Immunization During Pregnancy: Impact on the Infant

Maternal immunization has undergone a paradigm shift in recent years, as women and healthcare providers accept and recognize the benefits of this strategy not only for the pregnant woman but also for the developing fetus and young infant. This article reviews the evidence for active immunization during pregnancy, with an emphasis on perinatal and infant outcomes. Current recommendations for immunization during pregnancy are presented, with particular focus on the routinely recommended vaccines during pregnancy: influenza and Tdap (tetanus, diphtheria, and pertussis). We discuss future research directions, maternal vaccines in development, and considerations for optimizing and advancing this underutilized strategy.

Incidence of influenza virus infection among pregnant women: a systematic review

BACKGROUND

The World Health Organization (WHO) considers pregnant women to be a risk group for severe influenza disease. We conducted a systematic review to evaluate influenza disease incidence in pregnant women in order to inform estimates of influenza vaccine impact for low-resource countries.

METHODS

We performed electronic literature searches, targeting studies on the following outcomes in pregnant women: attack rate, hospitalization rate, intensive care unit admission rate, mortality rate, and disability-adjusted life years lost. Only original studies published in peer-reviewed journals that had laboratory confirmation for influenza virus infection and included population-based incidence rates with denominator data were included. We summarized study characteristics in descriptive tables and outcome-specific Forest plots. We generated summary incidence rates using random effects models and assessed statistical heterogeneity by visual examination of Forest plots, and by χ 2 and I2 tests.

RESULTS

We identified 1543 articles, of which nine articles met the study inclusion criteria. Five were case series, three were cohort studies, and one was a randomized controlled trial. Eight studies were from high-income countries, and one was from an upper middle-income country. Six studies reported results for pandemic influenza, and three reported seasonal influenza. Statistical heterogeneity was high for all outcomes, and methodologies and duration of surveillance varied considerably among studies; therefore, we did not perform meta-analyses.

CONCLUSIONS

Study quality was very low according to GRADE criteria. More data on influenza disease incidence in pregnant women, particularly in low- and middle-income countries and for seasonal influenza disease, are needed to inform public health decision-making.

A Systematic Review and Meta-Analysis of Influenza A Virus Infection During Pregnancy Associated with an Increased Risk for Stillbirth and Low Birth Weight

BACKGROUND/AIMS

Impaired pregnancy outcomes, such as low birth weight are associated with increased disease risk in later life, however little is known about the impact of common infectious diseases during pregnancy on birth weight. The study had two aims: a) to investigate risk factors of influenza virus infection during pregnancy, and b) to analyze the impact of influenza virus infection on pregnancy outcome, especially birth weight.

METHODS

Prospective and retrospective observational studies found in PubMed, MEDLINE, Embase, Google Scholar, and WangFang database were included in this meta analysis. Data of included studies was extracted and analyzed by the RevMan software.

RESULTS

Pregnant women with anemia (P=0.004, RR=1.46, 95% CI: 1.13-1.88), obesity (P<0.00001, RR=1.35, 95% CI: 1.25-1.46) and asthma (P<0.00001, RR=1.99, 95% CI: 1.67-2.37) had higher rates of influenza virus infection. Regarding birth outcomes, influenza A virus infection did not affect the likelihood for cesarean section. Mothers with influenza had a higher rate of stillbirth (P=0.04, RR=2.36, 95% CI: 1.05-5.31), and their offspring had low 5-minute APGR Scores (P=0.009, RR=1.39, 95% CI: 1.08-1.79). Furthermore, the rate for birth weight < 2500g (P=0.04, RR=1.71, 95% CI: 1.03-2.84) was increased.

CONCLUSION

Results of this study showed that anemia, asthma and obesity during pregnancy are risk factors influenza A virus infection during pregnancy. Moreover, gestational influenza A infection impairs pregnancy outcomes and increases the risk for low birth weight, a known risk factor for later life disease susceptibility.

A systematic review of administrative and clinical databases of infants admitted to neonatal units

OBJECTIVES

High quality information, increasingly captured in clinical databases, is a useful resource for evaluating and improving newborn care. We conducted a systematic review to identify neonatal databases, and define their characteristics.

METHODS

We followed a preregistered protocol using MesH terms to search MEDLINE, EMBASE, CINAHL, Web of Science and OVID Maternity and Infant Care Databases for articles identifying patient level databases covering more than one neonatal unit. Full-text articles were reviewed and information extracted on geographical coverage, criteria for inclusion, data source, and maternal and infant characteristics.

RESULTS

We identified 82 databases from 2037 publications. Of the country-specific databases there were 39 regional and 39 national. Sixty databases restricted entries to neonatal unit admissions by birth characteristic or insurance cover; 22 had no restrictions. Data were captured specifically for 53 databases; 21 administrative sources; 8 clinical sources. Two clinical databases hold the largest range of data on patient characteristics, USA's Pediatrix BabySteps Clinical Data Warehouse and UK's National Neonatal Research Database.

CONCLUSIONS

A number of neonatal databases exist that have potential to contribute to evaluating neonatal care. The majority is created by entering data specifically for the database, duplicating information likely already captured in other administrative and clinical patient records. This repetitive data entry represents an unnecessary burden in an environment where electronic patient records are increasingly used. Standardisation of data items is necessary to facilitate linkage within and between countries.

Intrauterine infection, immune system and premature birth

Preterm birth accounts for nearly one million deaths among children under five years of age, and although its etiopathogenesis is not fully elucidated, ascending intrauterine infection and fetal inflammatory response seem to be the main triggers. The intense inflammatory response mediated by IL-1β, TNF-α, PAF, IFN-γ and IL-6, PGE₂ and MMP-1 and MMP-9 causes fetal membrane damage and rupture, increased uterine contractions and biochemical and structural changes in the cervix. Furthermore, preterm neonates have deficient innate and adaptive immune responses characterized by reduced levels of IgG, opsonization and phagocytosis, as well as increased activation of Th1 cells in relation to Th2 cells. Therefore, this triad is favors the occurrence of neonatal complications, such as respiratory distress syndrome, necrotizing enterocolitis, retinopathy of prematurity and bronchopulmonary dysplasia. Due to serious maternal and child health complications of intrauterine infection, several studies have tried to identify biomarkers for the early diagnosis of this entity. This literature review aims to discuss the main scientific findings regarding the association between ascending intrauterine infection, immune system and preterm birth.

Febrile Rhinovirus Illness During Pregnancy Is Associated With Low Birth Weight in Nepal

Background

Adverse birth outcomes, including low birth weight (LBW), defined as <2500 grams, small-for-gestational-age (SGA), and prematurity, contribute to 60%–80% of infant mortality worldwide and may be related to infections during pregnancy. The aim of this study was to assess whether febrile human rhinovirus (HRV) illness is associated with adverse birth outcomes.

Methods

Active household-based weekly surveillance was performed for respiratory illness episodes in pregnant women as part of a community-based, prospective, randomized trial of maternal influenza immunization in rural Nepal. Rhinovirus (HRV) febrile illness episodes were defined as fever plus cough, sore throat, runny nose, and/or myalgia with HRV detected on mid-nasal swab. Multivariate regression analysis evaluated the association between febrile HRV respiratory illness and adverse birth outcomes.

Results

Overall, 96 (3%) of 3693 pregnant women had HRV-positive febrile respiratory illnesses. Infants born to pregnant women with HRV febrile illness had a 1.6-fold increased risk of being LBW compared with those with non-HRV febrile illness (28 of 96 [38%] vs 109 of 458 [24%]; relative risk [RR], 1.6; 95% confidence interval [CI], 1.1–2.3). No difference in risk of LBW was observed between infants born to mothers with non-HRV febrile respiratory illness and those without respiratory illness during pregnancy (109 of 458 [24%] vs 552 of 2220 [25%], respectively; RR, 1.0; 95% CI, 0.8–1.2).

Conclusions

Febrile illness due to rhinovirus during pregnancy was associated with increased risk of LBW in a rural South Asian population. Interventions to reduce the burden of febrile respiratory illness due to rhinovirus during pregnancy may have a significant impact on LBW and subsequent infant mortality.

Implementation of the Recommendation to Vaccinate Pregnant Women against Seasonal Influenza - Vaccination Rates and Acceptance

Introduction In Germany vaccination recommendations are revised annually and published by the Standing Committee on Vaccination at the Robert Koch Institute (STIKO). In 2010 the vaccination recommendations were amended to include the proposal that pregnant women in the 2nd trimester of pregnancy and pregnant women with additional underlying disease in the 1st trimester of pregnancy should be vaccinated against seasonal influenza. This paper reports on vaccination rates and the factors influencing them. Method A cross-sectional study was carried out in two level 1 perinatal centers in two different German federal states (Saarland and Rhineland-Palatinate) during the influenza seasons of 2012/2013 and 2013/2014. A total of 253 pregnant women were included in the study. Pregnant women were interviewed using a standardized, pre-tested questionnaire and asked whether they were aware of the recommendation to vaccinate against seasonal influenza and about possible factors which might influence their decision to be vaccinated. In addition, data from their vaccination certificates and pregnancy passports were evaluated. Results Overall, the records of only 19.5 % of the pregnant women showed that they had been vaccinated against influenza in pregnancy. Among the group of pregnant women who had a previous history of vaccinations against influenza the willingness to be vaccinated was high (43.3 %) and this figure was statistically significant. The vaccination rate was even higher (49.9 %) and even more statistically significant among pregnant women whose gynecologist or family physician had recommended that they should be vaccinated. In contrast, only 3.3 % of pregnant women who had not been given the recommendation to vaccinate by their physicians were vaccinated against influenza. Discussion The failure to recommend that pregnant women be vaccinated against influenza and women's lack of any previous experience of influenza vaccination were the main reasons for the inadequate influenza vaccination coverage in pregnancy. Conclusion One of the key points to increase the influenza vaccination rate is to intensify the counselling of the pregnant women through the gynecologist.

Report of the WHO technical consultation on the effect of maternal influenza and influenza vaccination on the developing fetus: Montreal, Canada, September 30-October 1, 2015

In 2012, the World Health Organization (WHO) released a position paper on influenza vaccination recommending that pregnant women have the highest priority for seasonal vaccination in countries where the initiation or expansion of influenza immunization programs is under consideration. Although the primary goal of the WHO recommendation is to prevent influenza illness in pregnant women, the potential benefits of maternal immunization in protecting young infants are also recognized. The extent to which maternal influenza vaccination may prevent adverse birth outcomes such as preterm birth or small-for-gestational-age birth, however, is unclear as available studies are in disagreement. To inform WHO about the empirical evidence relating to possible benefits of influenza vaccination on birth outcomes, a consultation of experts was held in Montreal, Canada, September 30-October 1, 2015. Presentations and discussions covered a broad range of issues, including influenza virus infection during pregnancy and its effect on the health of the mother and the fetus, possible biological mechanisms for adverse birth outcomes following maternal influenza illness, evidence on birth outcomes following influenza illness during pregnancy, evidence from both observational studies and randomized controlled trials on birth outcomes following influenza vaccination of pregnant women, and methodological issues. This report provides an overview of the presentations, discussions and conclusions.

DOHaD at the intersection of maternal immune activation and maternal metabolic stress: a scoping review

The prenatal environment is now recognized as a key driver of non-communicable disease risk later in life. Within the developmental origins of health and disease (DOHaD) paradigm, studies are increasingly identifying links between maternal morbidity during pregnancy and disease later in life for offspring. Nutrient restriction, metabolic disorders during gestation, such as diabetes or obesity, and maternal immune activation provoked by infection have been linked to adverse health outcomes for offspring later in life. These factors frequently co-occur, but the potential for compounding effects of multiple morbidities on DOHaD-related outcomes has not received adequate attention. This is of particular importance in low- or middle-income countries (LMICs), which have ongoing high rates of infectious diseases and are now experiencing transitions from undernutrition to excess adiposity. The purpose of this scoping review is to summarize studies examining the effect and interaction of co-occurring metabolic or nutritional stressors and infectious diseases during gestation on DOHaD-related health outcomes. We identified nine studies in humans - four performed in the United States and five in LMICs. The most common outcome, also in seven of nine studies, was premature birth or low birth weight. We identified nine animal studies, six in mice, two in rats and one in sheep. The interaction between metabolic/nutritional exposures and infectious exposures had varying effects including synergism, inhibition and independent actions. No human studies were specifically designed to assess the interaction of metabolic/nutritional exposures and infectious diseases. Future studies of neonatal outcomes should measure these exposures and explicitly examine their concerted effect.

Maternal influenza and birth outcomes: systematic review of comparative studies

BACKGROUND

Although pregnant women are considered at high risk for severe influenza disease, comparative studies of maternal influenza and birth outcomes have not been comprehensively summarised.

OBJECTIVE

To review comparative studies evaluating maternal influenza disease and birth outcomes.

SEARCH STRATEGY

We searched bibliographic databases from inception to December 2014.

SELECTION CRITERIA

Studies of preterm birth, small-for-gestational-age (SGA) birth or fetal death, comparing women with and without clinical influenza illness or laboratory-confirmed influenza infection during pregnancy.

DATA COLLECTION AND ANALYSIS

Two reviewers independently abstracted data and assessed study quality.

MAIN RESULTS

Heterogeneity across 16 studies reporting preterm birth precluded meta-analysis. In a subgroup of the highest-quality studies, two reported significantly increased preterm birth (risk ratios (RR) from 2.4 to 4.0) following severe 2009 pandemic H1N1 (pH1N1) influenza illness, whereas those assessing mild-to-moderate pH1N1 or seasonal influenza found no association. Five studies of SGA birth showed no discernible patterns with respect to influenza disease severity (pooled odds ratio 1.24; 95% CI 0.96-1.59). Two fetal death studies were of sufficient quality and size to permit meaningful interpretation. Both reported an increased risk of fetal death following maternal pH1N1 disease (RR 1.9 for mild-to-moderate disease and 4.2 for severe disease).

CONCLUSIONS

Comparative studies of preterm birth, SGA birth and fetal death following maternal influenza disease are limited in number and quality. An association between severe pH1N1 disease and preterm birth and fetal death was reported by several studies; however, these limited data do not permit firm conclusions on the magnitude of any association.

TWEETABLE ABSTRACT

Comparative studies are limited in quality but suggest severe pandemic H1N1 influenza increases preterm birth.