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

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).

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.

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].

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