Trends in the prevalence, risk and pregnancy outcome of multiple births with congenital anomaly: a registry-based study in 14 European countries 1984-2007.

Objective: To assess the public health consequences of the rise in multiple births with respect to congenital anomalies.

Design: Descriptive epidemiological analysis of data from population-based congenital anomaly registries.

Setting: Fourteen European countries.

Population: A total of 5.4 million births 1984-2007, of which 3% were multiple births.

Methods: Cases of congenital anomaly included live births, fetal deaths from 20 weeks of gestation and terminations of pregnancy for fetal anomaly.

Main Outcome Measures: Prevalence rates per 10,000 births and relative risk of congenital anomaly in multiple versus singleton births (1984-2007); proportion prenatally diagnosed, proportion by pregnancy outcome (2000-07). Proportion of pairs where both co-twins were cases.

Results: Prevalence of congenital anomalies from multiple births increased from 5.9 (1984-87) to 10.7 per 10,000 births (2004-07). Relative risk of nonchromosomal anomaly in multiple births was 1.35 (95% CI 1.31-1.39), increasing over time, and of chromosomal anomalies was 0.72 (95% CI 0.65-0.80), decreasing over time. In 11.4% of affected twin pairs both babies had congenital anomalies (2000-07). The prenatal diagnosis rate was similar for multiple and singleton pregnancies. Cases from multiple pregnancies were less likely to be terminations of pregnancy for fetal anomaly, odds ratio 0.41 (95% CI 0.35-0.48) and more likely to be stillbirths and neonatal deaths.

Conclusions: The increase in babies who are both from a multiple pregnancy and affected by a congenital anomaly has implications for prenatal and postnatal service provision. The contribution of assisted reproductive technologies to the increase in risk needs further research. The deficit of chromosomal anomalies among multiple births has relevance for prenatal risk counselling.