Risk of singleton preterm birth after prior twin preterm birth: a systematic review and meta-analysis

Exposure to low concentrations of PM2.5 and its constituents with preterm birth in Shenzhen, China: a retrospective cohort study

BACKGROUND

Due to the Air Pollution Prevention and Control Measures issued by the Chinese government, air quality has significantly improved, particularly with respect to PM2.5. However, studies on the relationship between low concentrations of PM2.5 and preterm birth (PTB) remain limited in China.

OBJECTIVE

To examine the associations between low concentrations of PM2.5 and its constituents and PTB.

METHODS

This retrospective cohort study was conducted from July 2021 to April 2023 in Shenzhen, China. Data on questionnaires and pregnancy outcomes were collected for each participant. Using the Tracking Air Pollution in China (TAP) dataset, we assessed the concentrations of PM2.5 and its chemical constituents, including sulfate (SO42-), nitrate (NO3-), organic matter (OM), black carbon (BC), and ammonium (NH4+). We applied a generalized additive model (GAM) to evaluate the relationship. The relationship between exposure to PM2.5 and its constituents and PTB was further examined using a method that combined dummy variable settings with trend tests. Stratified analysis was conducted to explore the potential factors.

RESULTS

Among 17,240 live-born infants, the rate of PTB was 6.0%, and the average exposure concentration of PM2.5 was 20.24 μg/m3. There were positive associations between PM2.5 and its constituents and PTB. With each interquartile range (IQR) increase in PM2.5 during the third trimester, the risk of PTB increased by 2.23 times. The exposure effects of sulfate (SO42-) and organic matter (OM) were comparable to the total PM2.5. The third trimester might be the critical susceptibility window. The risk was higher among women who conceived in the cold season and were exposed to higher temperatures during pregnancy.

CONCLUSION

Even at low levels, PM2.5 can still increase the risk of PTB, with varying health effects attributed to different constituents. This underscores the importance of further strengthening environmental management and characterizing the contributions of PM2.5 sources.

Recurrence Risk of Pregnancy Complications in Twin and Singleton Deliveries

OBJECTIVE

 This study aimed to estimate and compare the recurrence risk of preterm birth (PTB), gestational diabetes mellitus (GDM), gestational hypertension (GH), and preeclampsia and eclampsia (PE and E) in subsequent pregnancy groups (index-subsequent) of singleton-singleton (n = 49,868), twin-singleton (n = 448), and singleton-twin (n = 723) pregnancies.

STUDY DESIGN

 Birthing individuals from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Consecutive Pregnancy Study (2002-2010) with ≥ 2 singleton or twin deliveries were examined. Adjusted relative risks (aRR) and 95% confidence intervals (CI) for recurrent PTB, GDM, GH, and PE and E were estimated using Poisson regression models with robust variance estimators.

RESULTS

 The aRR of PTB and GDM ranged from 1.4 to 5.1 and 5.2 to 22.7, respectively, with the greatest recurrence relative risk for both conditions in singleton-singleton subsequent pregnancies (PTB: aRR = 5.1 [95% CI: 4.8-5.5], GDM: aRR = 22.7 [95% CI: 20.8-24.8]). The aRR of GH and PE and E ranged from 2.8 to 7.6 and 3.2 to 9.2, respectively, with the greatest recurrence relative risk for both conditions in twin-singleton subsequent pregnancies (GH: aRR = 7.6 [95% CI: 2.8-20.5], PE and E: aRR = 9.2 [95% CI: 2.9-28.6]).

CONCLUSION

 Recurrence relative risk was increased for PTB, GDM, GH, and PE and E in all subsequent pregnancy groups, which varied in magnitude based on the birth number of the index and subsequent pregnancy. This information provides insight into risk management for subsequent pregnancies including multiples.

KEY POINTS

· Recurrence risk for all conditions is persistent in all subsequent pregnancy groups.. · The magnitude of risk varies by the presence of multiples in the index or subsequent pregnancy.. · Singleton-singleton pregnancies are at the greatest risk of PTB.. · Singleton-singleton pregnancies are at the greatest risk of GDM.. · Twin-singleton pregnancies are at the greatest risk of hypertensive disorders..

Frequency and Risk Factors Associated with Prematurity: A Cohort Study in a Neonatal Intensive Care Unit

Background/Objectives: Prematurity rates remain high and represent a challenge for the public health systems of any country, with a high impact on neonatal mortality. This study aimed to evaluate the frequency and environmental and maternal-fetal risk factors for premature birth in a cohort of parturient women, with their newborns monitored in a neonatal intensive care unit at a private reference hospital. Methods: A cohort was carried out between 2013 and 2018 among parturient women living in a capital city in the Northeast of Brazil whose newborns were admitted to the neonatal intensive care unit. This study was approved by the Research Ethics Committee of the University of Fortaleza. The information collected comprised data from both medical records and hydrosanitary data from maternal homes. Results: The prevalence of prematurity among live births (n = 9778) between 2013 and 2018 at this hospital was 23%. The frequency of prematurity among those eligible (n = 480) was 76.9%, and the frequency of eligible premature babies (n = 369) in relation to the total number of births in this period was 3.8%. In the multivariate analysis, the significant risk factors for prematurity were primigravida (RR = 1.104, 95%CI: 1.004-1.213) and hypertensive syndromes during pregnancy (RR = 1.262, 95%CI: 1.161-1.371), and the significant protective factor was the highest number of prenatal consultations (RR = 0.924, 95%CI: 0.901-0.947). Conclusions: This study contributes to providing greater visibility to prenatal care and the understanding of complications during pregnancy and childbirth care. These results indicate the need to implement public policies that promote improvements in the population's living conditions and care for pregnant women to reduce premature births and, consequently, neonatal and infant mortality.

Recurrent preterm delivery following twin versus singleton preterm delivery: A retrospective cohort

OBJECTIVE

The main risk factor for preterm delivery (PTD; <37 gestational weeks) is having a history of PTD. The aim of this research was to compare the risk for recurrent PTD following twin versus singleton gestation PTD.

METHODS

A retrospective population-based cohort study was performed, including all women who had two consecutive pregnancies, the first of which ended with PTD. The incidence of PTD recurrence was compared between women with PTD in twin versus singleton gestation. Multivariable logistic models were used to study the association between twinning status and PTD recurrence, and specifically by gestational age of the first PTD, inter-pregnancy interval (IPI), and mode of conception.

RESULTS

The study population included 15 590 women, of whom 1680 (10.8%) had twins in their index pregnancy and 13 910 (89.2%) had singletons. The incidence of recurrent PTD was 10.5% (n = 177) following twin PTD versus 21.9% (n = 3044) following singleton PTD (adjusted odds ratio = 0.50, 95% confidence interval 0.32-0.76, while controlling for confounding variables). The results were consistent while stratifying by IPI, gestational age of the first PTD, or mode of conception.

CONCLUSIONS

Women with PTD in twin gestations are at lower risk for recurrent PTD compared with women with singleton PTD.

Risk factors for preterm birth: an umbrella review of meta-analyses of observational studies

BACKGROUND

Preterm birth defined as delivery before 37 gestational weeks is a leading cause of neonatal and infant morbidity and mortality. The aim of this study is to summarize the evidence from meta-analyses of observational studies on risk factors associated with PTB, evaluate whether there are indications of biases in this literature, and identify which of the previously reported associations are supported by robust evidence.

METHODS

We searched PubMed and Scopus until February 2021, in order to identify meta-analyses examining associations between risk factors and PTB. For each meta-analysis, we estimated the summary effect size, the 95% confidence interval, the 95% prediction interval, the between-study heterogeneity, evidence of small-study effects, and evidence of excess-significance bias. Evidence was graded as robust, highly suggestive, suggestive, and weak.

RESULTS

Eighty-five eligible meta-analyses were identified, which included 1480 primary studies providing data on 166 associations, covering a wide range of comorbid diseases, obstetric and medical history, drugs, exposure to environmental agents, infections, and vaccines. Ninety-nine (59.3%) associations were significant at P < 0.05, while 41 (24.7%) were significant at P < 10-6. Ninety-one (54.8%) associations had large or very large heterogeneity. Evidence for small-study effects and excess significance bias was found in 37 (22.3%) and 12 (7.2%) associations, respectively. We evaluated all associations according to prespecified criteria. Seven risk factors provided robust evidence: amphetamine exposure, isolated single umbilical artery, maternal personality disorder, sleep-disordered breathing (SDB), prior induced termination of pregnancy with vacuum aspiration (I-TOP with VA), low gestational weight gain (GWG), and interpregnancy interval (IPI) following miscarriage < 6 months.

CONCLUSIONS

The results from the synthesis of observational studies suggest that seven risk factors for PTB are supported by robust evidence. Routine screening for sleep quality and mental health is currently lacking from prenatal visits and should be introduced. This assessment can promote the development and training of prediction models using robust risk factors that could improve risk stratification and guide cost-effective preventive strategies.

TRIAL REGISTRATION

PROSPERO 2021 CRD42021227296.

Reassessing Preterm Birth Prevention After the Withdrawal of 17-α Hydroxyprogesterone Caproate

The U.S. Food and Drug Administration has recently withdrawn approval for 17-α hydroxyprogesterone caproate for prevention of recurrent preterm birth, and recent studies have called into question benefits of the pessary in the setting of a short cervix. Obstetric health care professionals are once again left with limited remaining options for preterm birth prevention. This narrative review summarizes the best current evidence on the use of vaginal progesterone, low-dose aspirin, and cerclage for the prevention of preterm birth; attempts to distill possible lessons learned from studies of progesterone and pessary, as well as their implementation into practice; and highlights areas where inroads into preterm birth prevention may be possible outside of the progesterone-aspirin-cerclage paradigm.

Risk factors for preterm labor: An Umbrella Review of meta-analyses of observational studies

Preterm birth defined as delivery before 37 gestational weeks, is a leading cause of neonatal and infant morbidity and mortality. Understanding its multifactorial nature may improve prediction, prevention and the clinical management. We performed an umbrella review to summarize the evidence from meta-analyses of observational studies on risks factors associated with PTB, evaluate whether there are indications of biases in this literature and identify which of the previously reported associations are supported by robust evidence. We included 1511 primary studies providing data on 170 associations, covering a wide range of comorbid diseases, obstetric and medical history, drugs, exposure to environmental agents, infections and vaccines. Only seven risk factors provided robust evidence. The results from synthesis of observational studies suggests that sleep quality and mental health, risk factors with robust evidence should be routinely screened in clinical practice, should be tested in large randomized trial. Identification of risk factors with robust evidence will promote the development and training of prediction models that could improve public health, in a way that offers new perspectives in health professionals.

GRADE Use in Evidence Syntheses Published in High-Impact-Factor Gynecology and Obstetrics Journals: A Methodological Survey

Objective: To identify and describe the certainty of evidence of gynecology and obstetrics systematic reviews (SRs) using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach. Method: Database searches of SRs using GRADE, published between 1 January 2016 to 31 December 2020, in the 10 "gynecology and obstetrics" journals with the highest impact factor, according to the Journal Citation Report 2019. Selected studies included those SRs using the GRADE approach, used to determine the certainty of evidence. Results: Out of 952 SRs, ninety-six SRs of randomized control trials (RCTs) and/or nonrandomized studies (NRSs) used GRADE. Sixty-seven SRs (7.04%) rated the certainty of evidence for specific outcomes. In total, we identified 946 certainty of evidence outcome ratings (n = 614 RCT ratings), ranging from very-low (42.28%) to low (28.44%), moderate (17.65%), and high (11.63%). High and very low certainty of evidence ratings accounted for 2.16% and 71.60% in the SRs of NRSs, respectively, compared with 16.78% and 26.55% in the SRs of RCTs. In the SRs of RCTs and NRSs, certainty of evidence was mainly downgraded due to imprecision and bias risks. Conclusions: More attention needs to be paid to strengthening GRADE acceptance and building knowledge of GRADE methods in gynecology and obstetrics evidence synthesis.

Consequences of cervical pessary for subsequent pregnancy: follow-up of randomized clinical trial (ProTWIN)

OBJECTIVE

To evaluate the effect of cervical pessary, as a strategy to prevent preterm birth (PTB), on the outcome of subsequent pregnancy and maternal quality of life 4 years after the index twin pregnancy.

METHODS

Between 2009 and 2012, the ProTWIN trial randomized women with a multiple pregnancy to pessary use vs standard care for the prevention of PTB. The trial showed no benefit in unselected women with a twin pregnancy, but showed a 60% reduction in poor perinatal outcomes in favor of the pessary group in the subgroup of women with a mid-trimester short cervix (cervical length < 38 mm). All women were invited to participate in a follow-up study 4 years after their participation in the ProTWIN trial. In this follow-up study, maternal quality of life was assessed using the EQ-5D-3L questionnaire and women were asked separate questions about subsequent pregnancies. Results were compared between women who were randomized to the pessary vs the control group in the ProTWIN trial by calculating relative risk (RR) and 95% CI. Subgroup analysis was performed for women with a mid-trimester short cervix (cervical length < 38 mm).

RESULTS

Of the 813 women included in the ProTWIN trial, 408 (50.2%) participated in this follow-up study, comprising 228 randomized to the pessary group and 180 to the control group in the original trial. The median interval between participation in the ProTWIN trial and participation in this follow-up study was 4.1 (interquartile range (IQR), 3.9-7.1) years. Ninety-eight (24.0%) participants tried to conceive after their participation in the ProTWIN trial. Of those, 22 (22.4%) women did not have a subsequent pregnancy (no difference between pessary and control groups), seven (7.1%) women had at least one miscarriage but no live birth, and 67 (68.4%) women had at least one live birth (35 in the pessary vs 32 in the control group; RR, 0.93 (95% CI, 0.8-1.07)). In two women, the pregnancy outcome was unknown. Preterm delivery (< 37 weeks of gestation) of the first live birth occurred in three women in the pessary vs one woman in the control group (all singleton; RR, 2.57 (95% CI, 0.28-23.44)). No differences were found between the pessary and control groups in the subgroup of women with mid-trimester short cervix, but the numbers analyzed were small. The median health state index score was 0.95 (IQR, 0.82-0.95), with no difference between the pessary and control groups.

CONCLUSION

Our findings suggest that there are no long-term effects of pessary use on the outcome of subsequent pregnancies and maternal quality of life. Data on obstetric outcome were limited due to the small numbers. © 2021 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Spontaneous preterm birth as a function of normal cervical length in low-risk women

OBJECTIVES

To identify if there is an increased risk for spontaneous preterm birth (sPTB) across the continuum of measured, normal cervical lengths (CL) in low-risk women.

METHODS

Retrospective cohort study of women with singleton pregnancies and no history of prior sPTB. Women were included if they underwent mid-trimester transvaginal CL measurement between February 2016 and August 2018 and had a measured, normal CL ≥25mm. Women were excluded for progesterone exposure, fetal anomalies, or an unmeasurable CL due to a poorly developed lower uterine segment. The primary study outcome was sPTB <37 weeks. Secondary outcomes included: sPTB <35 weeks, birth gestational age (GA), and the number of hospital evaluations for suspected preterm labor (PTL). Cervical length was considered in interval groups 25-29mm, 30-34mm, 35-39mm, 40-44mm, and ≥45mm. Outcomes were analyzed with χ² test of trend and as a continuum (linear models, logistic regression and ROC curve), where appropriate.

RESULTS

985 women were included. The incidence of sPTB <37 weeks was 3.7%, with a mean birth GA of 38.7 ± 2.4 weeks. The odds of sPTB <37 weeks decreased with increasing cervical length, considered in 5 mm intervals (odds ratio = 0.67; 95% confidence interval 0.49-0.90) and an increasing birth GA of 1 additional day for each CL increase of 3mm (p = .0002). Conversely, sPTB <35 weeks (p = .49) and mean hospital evaluations for PTL (p = .26) were similar across groups. The ROC curve area-under-the-curve for sPTB <37 weeks of 0.64 showed poor predictive value.

CONCLUSIONS

Among women without a history of sPTB, there was an association of decreased risk of sPTB <37 weeks and advanced delivery GA with increasing, but normal-range CL measurements. However, the association was poor and was not associated with spontaneous preterm birth <35 weeks, or the number of hospital evaluations for PTL.

Low-dose aspirin for primary prevention of adverse pregnancy outcomes in twin pregnancies: an observational cohort study based on propensity score matching

Background

Since the effectiveness of low-dose aspirin (LDA) in twin pregnancies is uncertain, we aimed to preliminarily assess whether LDA is beneficial in preventing preeclampsia in twin pregnancies.

Methods

This study is an observational study in two hospitals in China. Among 932 women, 277 in the First Affiliated Hospital of Chongqing Medical University were routinely treated with aspirin (100 mg daily) from 12 to 16 weeks to 35 weeks of gestational age, while 655 in Chongqing Health Center for Women and Children were not taking aspirin during pregnancy. We followed each subject and the individual details were recorded.

Results

LDA significantly reduced the risk of preeclampsia (RR 0.48; 95% CI 0.24–0.95) and preterm birth 34 weeks (RR 0.50; 95% CI 0.29–0.86) and showed possible benefits to lower the rate of SGA babies (RR 0.74; 95% CI 0.55–1.00). Moreover, the risk of postpartum hemorrhage was not increased by LDA (RR 0.89; 95% CI 0.35–2.26).

Conclusions

Treatment with low-dose aspirin in twin pregnancies could offer some protection against adverse pregnancy outcomes in the absence of significantly increased risk of postpartum hemorrhage.

Trial registration

Chinese Clinical Trial Registry (ChiCTR); ChiCTR-OOC-16008203, Retrospectively registered date: April 1st, 2016;

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-021-04217-2.

Prediction and Prevention of Spontaneous Preterm Birth: ACOG Practice Bulletin, Number 234

Preterm birth is among the most complex and important challenges in obstetrics. Despite decades of research and clinical advancement, approximately 1 in 10 newborns in the United States is born prematurely. These newborns account for approximately three-quarters of perinatal mortality and more than one half of long-term neonatal morbidity, at significant social and economic cost (1-3). Because preterm birth is the common endpoint for multiple pathophysiologic processes, detailed classification schemes for preterm birth phenotype and etiology have been proposed (4, 5). In general, approximately one half of preterm births follow spontaneous preterm labor, about a quarter follow preterm prelabor rupture of membranes (PPROM), and the remaining quarter of preterm births are intentional, medically indicated by maternal or fetal complications. There are pronounced racial disparities in the preterm birth rate in the United States. The purpose of this document is to describe the risk factors, screening methods, and treatments for preventing spontaneous preterm birth, and to review the evidence supporting their roles in clinical practice. This Practice Bulletin has been updated to include information on increasing rates of preterm birth in the United States, disparities in preterm birth rates, and approaches to screening and prevention strategies for patients at risk for spontaneous preterm birth.

Effect of second-trimester sonographic cervical length on the risk of spontaneous preterm delivery in different risk groups: A prospective observational multicenter study

INTRODUCTION

The aim of the study is to compare the effect of cervical length measured with transvaginal ultrasound in the second trimester on the risk of spontaneous preterm delivery (PTD) between different risk groups of asymptomatic women with a singleton pregnancy.

MATERIAL AND METHODS

This is a pre-planned exploratory analysis of the CERVIX study, a prospective blinded multicenter diagnostic accuracy study. Asymptomatic women with a singleton pregnancy were consecutively recruited at their second-trimester routine ultrasound examination at seven Swedish ultrasound centers. Cervical length was measured with transvaginal ultrasound at 18-20 weeks (Cx1; n = 11 072) and 21-23 weeks (Cx2, optional; n = 6288). The effect of cervical length on the risk of spontaneous PTD and its discriminative ability was compared between women with: (i) previous spontaneous PTD, late miscarriage or cervical conization (high-risk group; n = 1045); (ii) nulliparae without risk factors (n = 5173); (iii) parae without risk factors (n = 4740). Women with previous indicated PTD were excluded (n = 114). Main outcome measures were: effect of cervical length on the risk of spontaneous PTD expressed as odds ratio per 5-mm decrease in cervical length with interaction analysis using logistic regression to test whether the effect differed between groups, area under the receiver operating characteristic curve (AUC), sensitivity, specificity, number needed to screen to detect one spontaneous PTD.

RESULTS

The effect of cervical length at Cx2 on the risk of spontaneous PTD <33 weeks was similar in all groups (odds ratios 2.26-2.58, interaction p value 0.91). The discriminative ability at Cx2 was superior to that at Cx1 and was similar in all groups (AUC 0.69-0.76). Cervical length ≤25 mm at Cx2 identified 57% of spontaneous preterm deliveries <33 weeks in the high-risk group with number needed to screen 161. The number needed to screen for groups (ii) and (iii) were 1018 and 843.

CONCLUSIONS

The effect of cervical length at 21-23 weeks on the risk of spontaneous PTD <33 weeks is similar in high- and low-risk pregnancies. The differences in number needed to screen should be considered before implementing a screening program.

Perinatal Outcomes and Risk Factors for Preterm Birth in Twin Pregnancies in a Chinese Population: A Multi-center Retrospective Study

Background: Twin pregnancies are associated with an increased risk of adverse maternal and neonatal outcomes, mainly owing to prematurity. Few studies have evaluated the risk factors for preterm birth (PTB) in Chinese population. The objective of this study is to present the short-term maternal-neonatal outcomes, investigating the potential risk factors associated with preterm birth in Chinese twin pregnancies.

Methods: A multi-center retrospective study of women pregnant with twins ≥28 weeks of gestation was conducted. Maternal and neonatal outcomes were analyzed. Logistic regression was used to identify potential risk factors for PTB before 37, 34, and 32 weeks, respectively.

Results: A total of 3,288 twin pregnancies and 6,576 neonates were included in 99,585 pregnancies. The rate of twin pregnancy was 3.3%, while the PTB rate before 37, 34, and 32 weeks among this population were 62.1, 18.8, and 10.4%, respectively. Logistic regression revealed that monochorionicity [Odds ratio (OR) 3.028, 95% confident interval (CI) 2.489–3.683, P < 0.001], gestational weight gain (GWG) <10 kg (OR 2.285, 95% CI 1.563–3.339, P < 0.001) and GWG between 10 and 15 kg (OR 1.478, 95% CI 1.188–1.839, P < 0.001), preeclampsia (PE) (OR 3.067, 95% CI 2.142–4.390, P < 0.001), and intrahepatic cholestasis of pregnancy (ICP) (OR 3.122, 95% CI 2.121–4.596, P < 0.001) were the risk factors for PTB before 37 weeks. Monochorionicity (OR 2.865, 95% CI 2.344–3.501, P < 0.001), age < 25 years (OR 1.888, 95% CI 1.307–2.728, P = 0.001), and GWG <10 kg (OR 3.100, 95% CI 2.198–4.372, P < 0.001) were risk factors for PTB before 34 weeks. Monochorionicity (OR 2.566, 95% CI 1.991–3.307, P < 0.001), age younger than 25 years (OR 1.964, 95% CI 1.265–3.048, P = 0.003), and GWG <10 kg (OR 4.319, 95% CI 2.931–6.364, P < 0.001) were the risk factors for PTB before 32 weeks.

Conclusions: Monochorionicity and GWG <10 kg were two major risk factors for PTB before 32, 34, and 37 weeks, whereas maternal age, PE, and ICP were also risk factors for PTB in specific gestational age.