Role of structural birth defects in preterm delivery

Congenital heart defects and preterm birth: Outcomes from a referral center

BACKGROUND

Preterm birth and congenital heart defects are two major causes of neonatal and infant mortality. However, the relationship between them has not yet been fully clarified.

OBJECTIVE

To determine the prevalence and spectrum of congenital heart defects in preterms, the specific associations between categories of congenital heart defects and preterm birth and to establish the influence on outcomes.

METHODS

Observational, case-control analysis that included 448 live births with congenital heart defects born between 2003 and 2017. Preterm with congenital heart defects were the case subjects and term neonates with congenital heart defects the control subjects.

RESULTS

Of the newborns with congenital heart defects, 23% were preterm. The odds of congenital heart defects in preterm were twofold higher than for term neonates (p<0.0001), even when considering only those with severe congenital heart defects (p=0.0002). The odds in preterm were 9.2-fold higher for abnormalities of the atria and atrial septum (p<0.0001) and two-fold higher for abnormalities of the ventricles and ventricular septum (p<0.0001) compared with term neonates. The neonatal mortality rate in the preterm group was not statistically different from that of the term group with congenital heart defects (p=0.799) or severe congenital heart defects (p=0.554).

CONCLUSION

Preterm have more than twice as many congenital heart defects as term neonates. Although the etiology of prematurity between infants with congenital heart defects is still uncertain, our findings highlight a possible relationship between prematurity and congenital heart defects.

High risk of spontaneous preterm birth among infants with gastroschisis

We examined the association between gastroschisis and preterm birth (PTB, <37 weeks) by subtype. The sample was drawn from singleton live births in California from 2007 to 2012 contained in a birth cohort file maintained by the California Office of Statewide Health Planning and Development (n = 2,891,965; 1,421 with gastroschisis). Relative risks (RRs) and 95% confidence intervals (CIs) were calculated for PTB by gestational age (<34, 34-36, and any <37 weeks) and by type (spontaneous labor with intact membranes, preterm premature rupture of the membranes [PPROM], provider initiated) and were adjusted for maternal characteristics. Over 44.5% of infants with gastroschisis were born preterm because of spontaneous etiologies; notably, 8.4% of infants with gastroschisis were born <34 weeks because of spontaneous etiologies (adjusted RRs 9.1-12.2). Overall, 53.7% of infants with gastroschisis were born preterm compared with only 6.9% of infants without gastroschisis (adjusted RR 15.2, 95% CI 13.6-19.5) and are at particularly high risk of spontaneous PTB. Nearly 9% of infants with gastroschisis delivered <34 weeks, regardless of preterm etiology, indicating that these infants are at great risk for PTB morbidities in addition to the complications from gastroschisis.

Reproductive suppression, birth defects, and periviable birth

We argue that reproductive suppression has clinical implications beyond its contribution to the burden of spontaneous abortion. We theorize that the incidence of births before the 28th week of gestation, which contribute disproportionately to infant morbidity and mortality, varies over time in part due to reproductive suppression in the form of selection in utero. We further theorize that the prevalence of structural birth defects among survivors to birth from conception cohorts gauges selection in utero. We based these theories on literature positing that natural selection conserved mechanisms that spontaneously abort "risky" pregnancies including those otherwise likely to yield infants with structural birth defects or small-for-gestational age males. We test our theory using high-quality birth defect surveillance data. We identify 479,885 male infants exposed to strong selection defined as membership in conception cohorts ranked in the lowest quartile of odds of a birth defect among live-born females. We estimate the risk of periviable birth among these infants as a function of selective pressure as well as of mother's race/ethnicity and age. We find that male infants from exposed conception cohorts exhibited 10% lower odds of periviable birth than males from other conception cohorts. Our findings support the argument that selection in utero has implications beyond its contribution to the burden of spontaneous abortion.

Prevalence and Risk of Birth Defects Observed in a Prospective Cohort Study: The Hokkaido Study on Environment and Children's Health

BACKGROUND

Prevalence rates of all anomalies classified as birth defects, including those identified before the 22nd gestational week, are limited in published reports, including those from the International Clearinghouse for Birth Defects Surveillance and Research (ICBDSR). In our birth cohort study, we collected the data for all birth defects after 12 weeks of gestation.

METHODS

Subjects in this study comprised 19,244 pregnant women who visited one of 37 associated hospitals in the Hokkaido Prefecture from 2003 through 2012, and completed follow-up. All birth defects after 12 weeks of gestation, including 55 marker anomalies associated with environmental chemical exposures, were recorded. We examined parental risk factors for birth defects and the association between birth defects and risk of growth retardation.

RESULTS

Prevalence of all birth defects was 18.9/1,000 births. The proportion of patients with birth defects delivered between 12 and 21 weeks of gestation was approximately one-tenth of all patients with birth defects. Among those with congenital malformation of the nerve system, 39% were delivered before 22 weeks of gestation. All patients with anencephaly and encephalocele were delivered before 22 weeks of gestation. We observed different patterns of parental risk factors between birth defect cases included in ISBDSR and cases not included. Cases included in ISBDSR were associated with an increased risk of preterm birth. Cases not included in ISBDSR were associated with an increased risk of being small for gestational age at term.

CONCLUSIONS

Data from our study complemented the data from ICBDSR. We recommend that birth defects not included in ICBDSR also be analyzed to elucidate the etiology of birth defects.

Fetal de novo mutations and preterm birth

Preterm birth (PTB) affects ~12% of pregnancies in the US. Despite its high mortality and morbidity, the molecular etiology underlying PTB has been unclear. Numerous studies have been devoted to identifying genetic factors in maternal and fetal genomes, but so far few genomic loci have been associated with PTB. By analyzing whole-genome sequencing data from 816 trio families, for the first time, we observed the role of fetal de novo mutations in PTB. We observed a significant increase in de novo mutation burden in PTB fetal genomes. Our genomic analyses further revealed that affected genes by PTB de novo mutations were dosage sensitive, intolerant to genomic deletions, and their mouse orthologs were likely developmentally essential. These genes were significantly involved in early fetal brain development, which was further supported by our analysis of copy number variants identified from an independent PTB cohort. Our study indicates a new mechanism in PTB occurrence independently contributed from fetal genomes, and thus opens a new avenue for future PTB research.

Preterm birth is a prevalent pregnancy condition and leads to substantial morbidity and mortality. Its genetic association has been well observed, but the underlying etiology remains unclear. Current research has been focused on identifying risk factors in maternal genomes. In this study, we tested an unexplored hypothesis that preterm birth could be independently influenced by fetal genomes. We analyzed fetal de novo mutations, those not inherited from parents, from 816 trio families, and found preterm infants tended to have increased de novo mutation rates compared to infants born at term. Importantly, we also observed that these preterm-associated de novo mutations preferentially affect dosage sensitive genes that are essential in embryonic development, and these affected genes are involved in early fetal brain development. Overall, our study for the first time showed the fetal genetic contribution to preterm birth, and suggested abnormal fetal development as a potential cause for preterm birth.

Evaluating narrow windows of maternal exposure to ozone and preterm birth in a large urban area in Southeast Texas

The association between O3 exposure and preterm birth (PTB) remains unclear. We evaluated associations for three categories of PTB and O3 in Harris County, Texas, during narrow periods of gestation. We computed two sets of exposure metrics during every 4 weeks of pregnancy for 152,214 mothers who delivered singleton, live-born infants in 2005-2007, accounting first for temporal variability and then for temporal and spatial sources of variability in ambient O3 levels. Associations were assessed using multiple logistic regression. We also examined the potential for a fixed cohort bias. In the bias-corrected cohort where associations were somewhat stronger, elevated odds ratios (ORs) per 10 parts per billion increase in O3 exposure (county-level metric) were detected for the fifth (OR=1.08, 95% confidence interval (CI): 1.04-1.12), sixth (OR=1.05, 95% CI=1.01-1.09), and seventh (OR=1.07, 95% CI=1.03-1.10) 4-week periods of pregnancy for late PTB (33-36 completed weeks gestation), the fifth (OR=1.13, 95% CI=1.02-1.25) and seventh (OR=1.15, 95% CI=1.04-1.27) 4-week periods of pregnancy for moderate PTB (29-32 completed weeks gestation), and the fifth (OR=1.21, 95% CI=1.08-1.36) 4-week period of pregnancy for severe PTB (20-28 completed weeks gestation). Conversely, decreased odds were found in the first 4-week period of pregnancy for severe PTB (OR=0.83, 95% CI=0.74-0.94). Associations were slightly attenuated using the spatially interpolated (kriged) metrics, and for women who did not work outside of the home. Our analyses confirm reports in other parts of the United States and elsewhere with findings that suggest that maternal exposure to ambient levels of O3 is associated with PTB.

A spectrum project: preterm birth and small-for-gestational age among infants with birth defects

OBJECTIVE

The aim of this study is to investigate the association between birth defects (BDs), prematurity and small-for-gestational age (SGA) in a population-based sample.

STUDY DESIGN

Participants were singleton live births enrolled in the National Birth Defects Prevention Study, including 18 737 case infants with one or more BD and 7999 controls. Logistic regression models to evaluate associations between BDs, prematurity and fetal growth were computed while adjusting for covariates.

RESULT

Cases were significantly more likely to be born prematurely than controls, particularly at 24 to 28 weeks of gestation. The highest odds ratios for preterm birth were found for intestinal atresia, anencephaly, gastroschisis and esophageal atresia. Infants with BDs were also significantly more likely to be SGA than controls (17.2 and 7.8%).

CONCLUSION

Infants with BDs are more likely than controls to be born prematurely and SGA. Findings from this study present additional evidence demonstrating a complex interaction between the development of BDs, prematurity and intrauterine growth.

Maternal prepregnancy body mass index and risk of spontaneous preterm birth

BACKGROUND

Findings from studies examining risk of preterm birth associated with elevated prepregnancy body mass index (BMI) have been inconsistent.

METHODS

Within a large population-based cohort, we explored associations between prepregnancy BMI and spontaneous preterm birth across a spectrum of BMI, gestational age, and racial/ethnic categories. We analysed data for 989,687 singleton births in California, 2007-09. Preterm birth was grouped as 20-23, 24-27, 28-31, or 32-36 weeks gestation (compared with 37-41 weeks). BMI was categorised as <18.5 (underweight); 18.5-24.9 (normal); 25.0-29.9 (overweight); 30.0-34.9 (obese I); 35.0-39.9 (obese II); and ≥ 40.0 (obese III). We assessed associations between BMI and spontaneous preterm birth of varying severity among non-Hispanic White, Hispanic, and non-Hispanic Black women.

RESULTS

Analyses of mothers without hypertension and diabetes, adjusted for age, education, height, and prenatal care initiation, showed obesity categories I-III to be associated with increased risk of spontaneous preterm birth at 20-23 and 24-27 weeks among those of parity 1 in each race/ethnic group. Relative risks for obese III and preterm birth at 20-23 weeks were 6.29 [95% confidence interval (CI) 3.06, 12.9], 4.34 [95% CI 2.30, 8.16], and 4.45 [95% CI 2.53, 7.82] for non-Hispanic Whites, non-Hispanic Blacks, and Hispanics, respectively. A similar, but lower risk, pattern was observed for women of parity ≥ 2 and preterm birth at 20-23 weeks. Underweight was associated with modest risks for preterm birth at ≥ 24 weeks among women in each racial/ethnic group regardless of parity.

CONCLUSIONS

The association between women's prepregnancy BMI and risk of spontaneous preterm birth is complex and is influenced by race/ethnicity, gestational age, and parity.

Ten-year review of major birth defects in VLBW infants

OBJECTIVE

Birth defects (BDs) are an important cause of infant mortality and disproportionately occur among low birth weight infants. We determined the prevalence of BDs in a cohort of very low birth weight (VLBW) infants cared for at the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network (NRN) centers over a 10-year period and examined the relationship between anomalies, neonatal outcomes, and surgical care.

METHODS

Infant and maternal data were collected prospectively for infants weighing 401 to 1500 g at NRN sites between January 1, 1998, and December 31, 2007. Poisson regression models were used to compare risk of outcomes for infants with versus without BDs while adjusting for gestational age and other characteristics.

RESULTS

A BD was present in 1776 (4.8%) of the 37 262 infants in our VLBW cohort. Yearly prevalence of BDs increased from 4.0% of infants born in 1998 to 5.6% in 2007, P < .001. Mean gestational age overall was 28 weeks, and mean birth weight was 1007 g. Infants with BDs were more mature but more likely to be small for gestational age compared with infants without BDs. Chromosomal and cardiovascular anomalies were most frequent with each occurring in 20% of affected infants. Mortality was higher among infants with BDs (49% vs 18%; adjusted relative risk: 3.66 [95% confidence interval: 3.41-3.92]; P < .001) and varied by diagnosis. Among those surviving >3 days, more infants with BDs underwent major surgery (48% vs 13%, P < .001).

CONCLUSIONS

Prevalence of BDs increased during the 10 years studied. BDs remain an important cause of neonatal morbidity and mortality among VLBW infants.

Are black and Hispanic infants with specific congenital heart defects at increased risk of preterm birth?

Congenital heart defects (CHDs) are a leading cause of infant morbidity and mortality. Infants with CHDs have increased risk of preterm birth (PTB) compared to infants without birth defects. Although non-Hispanic (NH) Blacks are more likely to be born preterm and Hispanics have rates similar to those of PTB to NH-Whites, it is unknown if this pattern is present for infants with specific types of CHDs. Our intent was to determine if defect-specific risk of PTB varies by maternal race/ethnicity among infants with CHDs. We conducted a retrospective cohort study with 14,888 singleton infants from the Florida Birth Defects Registry, born in 1998-2003 to resident NH-White, NH-Black, and Hispanic women aged 15-49, diagnosed with 11 CHDs. Covariates were taken from Florida live birth certificates. PTB was defined as 20-36 weeks of gestation. Odds ratios (OR) and P-values were calculated from defect-specific multivariable logistic regression models; statistical significance was set at P < 0.002. The greatest risk of PTB was for NH-Black infants with conotruncal CHDs. NH-Blacks with common truncus, transposition of the great vessels, and tetralogy of Fallot had increased risk of PTB compared to NH-Whites (OR = 4.8, P = 0.015; OR = 3.1, P = 0.004; and OR = 2.0, P = 0.005, respectively). Hispanics with conotruncal CHDs had almost a twofold risk of PTB compared to NH-Whites (P > 0.002). NH-Blacks with tricuspid valve atresia/stenosis had 4.1 times (P = 0.034) and Hispanics had 2.1 times (P = 0.314) the risk for PTB compared to NH-Whites. NH-Blacks with hypoplastic left heart syndrome had 2.0 times (P = 0.047) the risk for PTB as NH-Whites. Both NH-Black and Hispanic infants with CHDs may be at increased risk of PTB, depending on the type of CHD, but the etiology is unknown. Future research is needed to further examine this complex relationship.

Orofacial clefts in the National Birth Defects Prevention Study, 1997-2004

Orofacial clefts are among the most common types of birth defects, but their clinical presentation has not been well described in a geographically diverse US population. To describe the birth prevalence and phenotype of nonsyndromic clefts, we used data from the National Birth Defects Prevention Study (NBDPS), a multi-site, population-based, case-control study aimed at identifying genetic and environmental risk factors for birth defects. Included in the study were infants born during 1997-2004 with a cleft lip (CL), cleft lip with cleft palate (CLP), or cleft palate (CP). Infants with clefts associated with recognized single-gene disorders, chromosome abnormalities, holoprosencephaly, or amniotic band sequence were excluded. A total of 3,344 infants with nonsyndromic orofacial clefts were identified, including 751 with CL, 1,399 with CLP, and 1,194 with CP, giving birth prevalence estimates of 0.3, 0.5, and 0.4/1,000 live births, respectively. Among infants with CLP where cleft laterality was specified, about twice as many had unilateral vs. bilateral involvement, while for CL there were over 10 times as many with unilateral versus bilateral involvement. Involvement was most often left-sided. About one-quarter of infants with CP had Pierre Robin sequence. Over 80% of infants had an isolated orofacial cleft. Among infants with CL or CLP, heart, limb, and other musculoskeletal defects were most commonly observed, while heart, limb, and central nervous system defects were most common among infants with CP. Better understanding of the birth prevalence and phenotype may help guide clinical care as well as contribute to an improved understanding of pathogenesis.

Association of preterm birth with brain malformations

This study investigates the rate of preterm birth in babies with congenital brain defects. Autopsy case reports of congenital brain anomalies were obtained from the literature. The control cases were from a large registry, a published report from the Metropolitan Atlanta Congenital Defects Program. From 428 publications, 1168 cases were abstracted that had autopsy studies of congenital brain defects and information on the gestational age (GA) at birth. The control data from Atlanta included 7738 infants with significant birth defects of any kind and 264,392 infants without birth defects. In the autopsy cases with brain defects, the mean GA was 36.6 wk, whereas the Atlanta data showed a mean GA of 39.3 wk for infants with no defects and a significantly shorter gestation of 38.1 wk (p < 0.0001) for infants with defects. In the Atlanta data, the rate of preterm birth was 9.3% for those with no defects compared with 21.5% (p < 0.0001) for those with defects. In the autopsy cases with brain defects, the rate of preterm birth was even greater (33.1%, p < 0.0001). In conclusion, these data show an association of brain defects with preterm births.

Preterm birth in pregnancies complicated by major congenital malformations: a population-based study

OBJECTIVE

The objective of the study was to estimate and compare the relative risk of preterm birth (PTB) in pregnancies complicated by 1 or more of 8 major congenital malformations (MCMs).

STUDY DESIGN

This was a population-based cohort study of the birth database of the Missouri Department of Health (1989-1997) including 678,693 singleton live births. Outcomes included a binary composite variable of any MCM and the following 8 individual malformations: spina bifida, diaphragmatic hernia, renal agenesis, other urogenital anomaly, tracheoesophageal fistula/esophageal atresia, omphalocele/gastroschisis, cardiac defect, and cleft lip/palate. Chromosomal anomalies were excluded. Logistic regression analyses assessed the association between malformations and PTB.

RESULTS

The risk of PTB increased significantly and to varying degrees for each malformation. In pregnancies with any MCM, there was an increased prevalence (11.5%) and relative risk (adjusted odds ratio [(adj)OR] 3.2 [95% confidence interval (CI) 2.9 to 3.6]) of PTB at less than 35 weeks' gestation. The magnitude of risk increase was greatest at the earliest gestational ages: (adj)OR 4.8 (95% CI, 4.0 to 5.7) at less than 28 weeks. Pregnancies with multiple malformations were at highest risk for PTB: (adj)OR 8.0 [95% CI, 4.6 to 14.1].

CONCLUSION

MCMs significantly increase PTB risk. The risk varies by malformation type and is higher with multiple malformations.

Outcome after preterm delivery of infants antenatally diagnosed with congenital heart disease

OBJECTIVE

To determine outcome of delivery before 36 weeks gestation in babies diagnosed antenatally with serious congenital heart disease (CHD).

STUDY DESIGN

A retrospective database review at 2 tertiary care fetal cardiology centers. Details of neonatal course and outcome were obtained for those antenatally diagnosed with serious CHD who were live born before 36 weeks gestation.

RESULTS

Between January 1998 and December 2002, 9918 women were referred for fetal echocardiography. Serious CHD was diagnosed in 1191 fetuses (12%), of which 46 (4%) delivered prematurely. Median gestation was 33 (range 24-35) weeks, and median birth weight 1.56 (0.50-3.59) kg. Extracardiac/karyotypic anomalies occurred in 23 (50%). Twenty-six babies (57%) underwent neonatal surgery: 16 a cardiac procedure, 5 a general surgical procedure, and 5 both. Eight died during or after operation (31%). Two babies underwent interventional heart catheterization; both died. The overall mortality rate was 72%. Extracardiac/karyotypic anomalies increased the relative risk of death by a factor of 1.36. Mean hospital stay for those surviving to initial discharge was 46 (2-137) days.

CONCLUSIONS

There is a very high morbidity and mortality rate in this group, particularly for those with extracardiac/karyotypic anomalies. This should be reflected in decisions over elective preterm delivery and when counseling parents.

Is Older Maternal Age a Risk Factor for Preterm Birth and Fetal Growth Restriction? A SystematicReview

To determine if there was an association between advancing maternal age and adverse pregnancy outcomes (preterm delivery and small-for-gestational-age births), a systematic review was conducted based on a comprehensive search of the literature from 1985 to 2002. Ten studies met the following inclusion criteria: (1) assessed risk factors for preterm birth by subtype (i.e., idiopathic preterm labor, preterm premature rupture of membranes) and small-for-gestational-age (SGA) birth (fetal growth restriction); (2) used acceptable definitions of these outcomes; (3) were published between January 1985 and December 2002; (4) were restricted to studies that have considered preterm birth due to idiopathic preterm labor or premature rupture of membranes or both; (5) were restricted to singleton live births; (6) were conducted in a developed country; and (7) were published in English. The majority of the studies reviewed found that older maternal age was associated with preterm birth. There is insufficient evidence to determine if older maternal age is an independent and direct risk factor for preterm birth and SGA birth, or a risk marker that exerts its influence on gestational age or birth weight or both through its association with age-dependent confounders. Future research is needed to quantify the independent and unconfounded impact of delayed childbearing on neonatal outcomes, as well as to identify the pathways involved.

Second trimester folate status and preterm birth

OBJECTIVE

The purpose of this study was to show that maternal folate status during pregnancy may be related to preterm birth.

STUDY DESIGN

Women were recruited at 24 to 29 weeks' gestation from 1995 to 2000 into the Pregnancy, Infection, and Nutrition Study. Those who completed an interview and a food frequency questionnaire, or provided a blood sample for radioassay of serum (n = 2026) and red blood cell (n = 1034) folate were included.

RESULTS

Mean daily dietary folate intake was 463 microg (SD +/- 248). Intake </=500 microg was associated with increased preterm delivery (RR = 1.8, 95% CI 1.4-2.6) controlling for total energy intake. Serum folate levels <16.3 ng/mL and red blood cell folate levels </=626.6 ng/mL yielded adjusted risk ratios of 1.8 (95% CI 1.3-2.5) and 1.7 (95% CI 1.1-2.6), respectively. Patterns were similar for spontaneous and overall preterm birth.

CONCLUSION

These results support the hypothesis that low folate levels during the second trimester of pregnancy are associated with an increased risk of preterm birth.