Comparative epidemiology of sudden infant death syndrome and sudden intrauterine unexplained death

The Role of Infection and Inflammation in Stillbirths: Parallels with SIDS?

It has been suggested that stillbirths are part of the spectrum of infant deaths that includes sudden infant death syndrome (SIDS). This paper examines the hypothesis that risk factors associated with stillbirths might contribute to dysregulation of inflammatory responses to infections that could trigger the physiological responses leading to fetal loss. These include genetic factors (ethnic group, sex), environmental (infection, cigarette smoke, obesity), and developmental (testosterone levels) factors. Interactions between the genetic, environmental, and developmental risk factors are also considered, e.g., the excess of male stillborn infants in relation to the effects of testosterone levels during development on pro-inflammatory responses. In contrast to SIDS, inflammatory responses of both mother and fetus need to be considered. Approaches for examining the hypothesis are proposed.

Maternal smoking and the risk of still birth: systematic review and meta-analysis

Background

Smoking in pregnancy is known to be associated with a range of adverse pregnancy outcomes, yet there is a high prevalence of smoking among pregnant women in many countries, and it remains a major public health concern. We have conducted a systematic review and meta-analysis to provide contemporary estimates of the association between maternal smoking in pregnancy and the risk of stillbirth.

Methods

We searched four databases namely MEDLINE, EMBASE, Psych Info and Web of Science for all relevant original studies published until 31^st December 2012. We included observational studies that measured the association between maternal smoking during pregnancy and the risk of stillbirth.

Results

1766 studies were screened for title analysis, of which 34 papers (21 cohorts, 8 case controls and 5 cross sectional studies) met the inclusion criteria. In meta-analysis smoking during pregnancy was significantly associated with a 47% increase in the odds of stillbirth (OR 1.47, 95% CI 1.37, 1.57, p < 0.0001). In subgroup analysis, smoking 1-9 cig/day and ≥10 cig/day was associated with an 9% and 52% increase in the odds of stillbirth respectively. Subsequently, studies defining stillbirth at ≥ 20 weeks demonstrated a 43% increase in odds for smoking mothers compared to mothers who do not smoke, (OR 1.43, 95% CI 1.32, 1.54, p < 0.0001), whereas studies with stillbirth defined at ≥ 24 weeks and ≥ 28 weeks showed 58% and 33% increase in the odds of stillbirth respectively.

Conclusion

Our review confirms a dose-response effect of maternal smoking in pregnancy on risk of stillbirth. To minimise the risk of stillbirth, reducing current smoking prevalence in pregnancy should continue to be a key public health high priority.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-015-1552-5) contains supplementary material, which is available to authorized users.

Effect of maternal body mass index on cord blood erthropoietin concentrations

OBJECTIVE

To examine the hypothesis that maternal body mass index (BMI) (an index of maternal adiposity) correlates with cord blood concentrations of erythropoietin (EPO).

STUDY DESIGN

Cross-sectional cohort study of consecutively born singleton term healthy infants born to mothers with various BMIs. Excluded were infants with major factors known to be associated with a potential increase in fetal erythropoiesis. Prepregnancy maternal BMI was calculated from maternal recollection.

RESULT

There was a significant correlation between EPO concentrations and maternal BMI (R = 0.427, P = 0.007). This correlation remained significant in multiple stepwise regression analysis using the EPO concentration as the dependent variable, and maternal age, parity, gestational age and Apgar scores (1 or 5 min) as potential confounders.

CONCLUSION

Cord blood concentrations of EPO correlate with maternal BMI. We speculate that increasing maternal BMI may represent a relative hypoxic burden on the fetus.

Maternal smoking and increased risk of sudden infant death syndrome: a meta-analysis

Maternal smoking is detrimental to the development of fetuses and neonates. This meta-analysis was performed to measure the accumulated association of sudden infant death syndrome (SIDS) risk with both prenatal and postnatal maternal smoking. The odds ratio (OR) corresponding to the 95% confidence interval (CI) was used to assess the associations between maternal smoking and SIDS risk. The statistical heterogeneity among studies was assessed with the Q-test and I(2) statistics. The data for this meta-analysis were available from 35 case-control studies. The prenatal and postnatal maternal smoking was associated with a significantly increased risk of SIDS (OR=2.25, 95% CI=2.03-2.50 for prenatal maternal smoking analysis, and OR=1.97, 95% CI=1.77-2.19 for postnatal maternal smoking analysis, respectively) by random effects model. After stratified analyses, regardless of prenatal or postnatal smoking, heavy cigarette consumption increased the risk of SIDS and significantly elevated SIDS risk was found to be associated with co-sleeping with postnatal smoking mothers. Our results suggested that maternal smoking were associated with elevated SIDS risk, the effects were dose-dependent. In addition, SIDS risk was significantly increased in infants co-sleeping with postnatal smoking mothers.

Male sex and pre-existing diabetes are independent risk factors for stillbirth

AIM

To determine whether the risk of stillbirth is associated with male fetal sex, fetal growth and maternal factors in an Australian population.

METHODS

A retrospective secondary data analysis of 16 445 singleton births was performed using a tertiary referral centre obstetric database (1995-1999). Univariate and multiple logistic regression analyses were performed.

RESULTS

Stillbirth complicated 1% of the pregnancies in the study population, and 59% of stillbirths were associated with a male fetus. Significant characteristics associated with stillbirth were intrauterine growth restriction (IUGR), birth defects, gestational age, Aboriginal ethnicity, previous stillbirth, parity greater than three and placental abruption. Male stillbirths were more likely to occur at a later gestation (median gestation 30.5 weeks, range 20-43 weeks) compared to females (median 25 weeks, range 20-40 weeks), P = 0.01. Sixty per cent of IUGR fetuses were female (P < 0.001). Male sex (odds ratio (OR) 1.5, confidence interval (CI) 1.01, 2.17, P = 0.04) and maternal type 1 diabetes (OR 4.7, CI 1.58, 14.19, P = 0.006) were independently associated with stillbirth.

CONCLUSION

Male fetal sex and pre-existing diabetes are independent risk factors for stillbirth. Diabetes remains a significant risk for stillbirth even with contemporary monitoring and clinical management. Those diabetic pregnancies where the fetus is male require appropriate monitoring and timely interventions to achieve an optimal outcome.

Combined effects of cigarette smoking and alcohol consumption on perinatal outcome

BACKGROUND

An increase in various congenital abnormalities associated with cigarette smoking and the use of alcohol during pregnancy has been reported in many studies. These exposures also increase the risk of pregnancy complications such as abruptio placentae, unexplained stillbirth, preterm labor and intrauterine growth restriction. However, very few studies have addressed the combined effect of smoking and drinking on pregnancy outcomes.

METHODS

In this review, the adverse effects of smoking or drinking on pregnancy were obtained from publications in which both substances were addressed in the same study population. A special effort was made to find studies in which the combined effect of these substances was investigated.

RESULTS

Preterm labor occurred more frequently in women who drank and smoked during pregnancy. This increased odds ratio was more than the sum of the effects of either smoking or drinking, indicating that the use of both substances by the same woman has a synergistic effect that increases the risk of preterm labor. This synergistic effect was also found for low birth weight and growth restriction.

CONCLUSIONS

As most of the women who drink during pregnancy also smoke cigarettes, attention should be given to the prevention or reduced use of both substances during pregnancy.

Social inequality in fetal and perinatal mortality in the Nordic countries

Aim: The aim of this study is to review the epidemiological literature from the past 27 years on social inequality in fetal and perinatal mortality in the Nordic countries in order to examine whether social inequalities in fetal and perinatal mortality exist, and whether there are differences between the countries. Methods: The databases MEDLINE and EMBASE were searched for Nordic epidemiological studies published between January 1980 and August 2007 about the association between social indicators and the outcomes spontaneous abortion, stillbirth or perinatal mortality. Thirty-five studies that fulfilled the inclusion criteria were identified for this review. Results: Social differences in stillbirth and perinatal mortality were found in all of the identified Finnish and Norwegian studies and in the majority of studies from Denmark, whereas in the Swedish studies the findings were less consistent. As only a small number of studies on spontaneous abortion were identified (n=3), no conclusions were drawn with regard to this outcome. Conclusions: There seems to be a reasonable body of evidence that social inequality in stillbirth and perinatal mortality exists in Norway, Finland and Denmark, whereas the conclusions regarding Sweden are more uncertain. A number of methodological problems complicate the comparison of the findings. Nordic collaborative analyses of social gradients in spontaneous abortion, stillbirth and perinatal mortality, which take these methodological concerns into account, are needed in order to draw inferences across countries.

Neonatal nucleated red blood cells in infants of overweight and obese mothers

OBJECTIVE

The perinatal outcome of the infant of obese mother is adversely affected and in theory, may involve fetal hypoxia. We hypothesized that an index of fetal hypoxia, the neonatal nucleated red blood cell (NRBC) count, is elevated in infants of overweight and obese mothers.

STUDY DESIGN

Absolute NRBC counts taken during the first 12 hours of life in 41 infants of overweight and obese mothers were compared to 28 controls.

RESULTS

Maternal body mass index and infant birthweight were significantly higher in the overweight and obese group (P < 0.01). Hematocrit, corrected white blood cell and lymphocyte counts did not differ between groups. The absolute NRBC count was higher (P = 0.01), and the platelet count lower (P = 0.05) in infants of overweight and obese mothers than in controls. In stepwise regression analysis, the absolute NRBC count in infants of overweight and obese mothers remained significantly higher even after taking into account birthweight or gestational age and Apgar scores (P < 0.02).

CONCLUSION

Infants of overweight and obese mothers have increased nucleated red blood cells at birth compared with controls. We speculate that even apparently healthy fetuses of overweight and obese mothers are exposed to a subtle hypoxemic environment.

Clinicopathological evaluation of 59 cases of fetal death

OBJECTIVE

The purpose of this study has been assessing the determinants of stillbirth among the newborns of the Verona University Obstetrics Department.

MATERIALS AND METHODS

A total of 59 stillbirth cases, observed between January 2000 and June 2006, were retrospectively studied. WHO definition for stillbirth was adopted as the inclusion criterion. Clinical files, feto-maternal laboratory data, feto-placental pathology findings as well as delivery mode and circumstances were all systematically reviewed.

RESULTS

The 59 observed cases correspond to an incidence of 9.8 stillbirths/year, which, considering the institutional delivery rate, correspond to 5.4 cases per 1000 births. Frequent relevant conditions associated with stillbirth were intrauterine growth restriction (15.2%), congenital fetal anomalies (13.5%), various maternal diseases (21.0%); no cause of fetal demise could be found in 10/59 (17.0%) cases, which were classified as unexplained. Most deliveries were successfully induced with prostaglandins except 11 cases (19.0%) which required a C-section due to severe maternal conditions associated with the fetal loss.

CONCLUSION

Thorough investigation of each individual stillbirth case, by means of an integrated study protocol, along with the Pathologist's close collaboration, allows identification of a likely cause in the majority of cases. Better knowledge of unexpected fetal loss is the premise for better parental counselling and for prevention of recurrences.

Elevated risks of pregnancy complications and adverse outcomes with increasing maternal age

BACKGROUND

In the USA, between 1980 and 2004, the proportion of all births increased 2-fold in women aged > or = 30, 3-fold in women aged > or = 35 and nearly 4-fold in women aged > or = 40. The objective of this study was to evaluate the risks of pregnancy complications and adverse outcomes with increasing maternal age using national vital statistics data.

METHODS

The study population included 8,079,996 live births of singletons of > or = 20 weeks among women aged 30-54 from the 1995-2000 US Birth Cohort Linked Birth/Infant Death Data Set. Outcomes were modelled by maternal age and parity using multinomial logistic regression to calculate adjusted odds ratios (AORs) and 95% confidence intervals.

RESULTS

The risks for most outcomes paralleled increasing maternal age including prolonged and dysfunctional labour, excessive labour bleeding, breech and malpresentation and primary Caesarean delivery. The highest AORs among women aged > or = 45 versus 30-34 by parity (primiparas and multiparas, respectively) were for chronic hypertension (3.70, 4.89), diabetes (2.19, 2.58), primary Caesarean (3.14, 2.85), excessive labour bleeding (1.54, 1.49), pregnancy hypertension (1.55, 2.13) and birth <32 weeks (2.11, 1.77).

CONCLUSIONS

Increasing maternal age is associated with significantly elevated risks for pregnancy complications and adverse outcomes, which vary by parity.

Teratology public affairs committee position paper: Maternal obesity and pregnancy

Compared to normal-weight women, obese women have an increased risk of infertility and pregnancy complications. The most consistently described pregnancy complications are hypertensive disorders, gestational diabetes mellitus, thromboembolic events, and cesarean section. Fetal and neonatal complications may include congenital malformations, macrosomia, and shoulder dystocia. The literature suggests that women with a body mass index (BMI) >or=30 have approximately double the risk of having a child with a neural tube defect (NTD) compared to normal-weight women, and the increased risk associated with higher maternal body weight does not appear to be modified by folic acid supplementation. The Public Affairs Committee of the Teratology Society supports the public health initiatives identified by the U.S. Food and Drug Administration in 2004 and the research initiatives identified by the National Institutes of Health in 2004. The Public Affairs Committee recommends that clinicians counsel women about appropriate caloric intake and exercise and that health-care providers educate parents about appropriate childhood nutrition. Breast-feeding should be encouraged based on evidence of a protective effect against childhood obesity, as well as other health advantages.

Perinatal periods of risk: analysis of fetal-infant mortality rates in Kansas City, Missouri

OBJECTIVES

The Perinatal Periods of Risk (PPOR) technique was used to analyze resident fetal and infant death data from Kansas City, Missouri, for the period 1998-2002. Results offer important information that can be used to develop community-based prevention strategies related to racial/ethnic disparities in infant mortality rates (IMR).

METHODS

The PPOR approach for fetal and infant mortality can be mapped by birthweight at delivery and time of death into four strategic prevention areas: 1) Maternal Health/Prematurity (MHP), 2) Maternal Care (MC), 3) Newborn Care (NC), and 4) Infant Health (IH). For this analysis, all fetal and infant death certificates from the metropolitan Kansas City area were linked to their birth certificates and those associated with residents of Kansas City, Missouri, proper were used to create the dataset used in this analysis. Due to the small number of fetal and infant deaths among other ethnic groups, the analysis was restricted to a comparison of the disparity of IMR between Blacks, Whites, and a national non-Hispanic white reference group. The Kitagawa formula was used to determine contribution to excess deaths from birthweight-specific mortality and birthweight distribution rates. Logistic regression techniques were used to identify risk factors for death among Black fetuses and infants with very low birthweights and also deaths due to sudden infant death syndrome (SIDS).

RESULTS

The PPOR analysis showed that of the excess deaths among black infants, when compared to a national reference group, 47% was attributable to MHP and another 29% was attributable to IH. Differences in MC and NC only accounted for 27 and 8% of the total excess deaths. During the study period, rates of sudden infant death syndrome (SIDS) were found to be significantly higher among Blacks as compared to Whites (2.12 vs. 0.81 per 1,000). An analysis of maternal characteristics for SIDS deaths among blacks using a step-wise logistic regression model, found that maternal age less than 20 years old, previous births, inadequate prenatal care, and being a Medicaid recipient were significant-adjusted odds ratios of 23.7 (95% Cl 10.48, 53.67), 8.4 (95% Cl 3.64, 19.21), 2.9 (95% Cl 1.38, 6.05) and 2.5 (95% Cl 1.04, 5.84), respectively.

CONCLUSIONS

PPOR is an easy to use approach that helps focus community initiatives for improving maternal and infant health. In Kansas City, Missouri, efforts to further lower IMR in blacks can be achieved through the reduction of risk factors affecting maternal health and through maternal education to improve infant health.