Risk Factors for Congenital Anomaly in a Multiethnic Birth Cohort

Abstract

Infant mortality rates vary considerably among ethnic groups in the United Kingdom, with the highest rates in Pakistani infants. The most common causes of infant death are related to immaturity, but in Pakistani babies, the most common cause is congenital anomalies, including consanguineous unions. The disparity in risk of congenital anomalies cannot be totally explained by socioeconomic differences between Pakistani and white British groups. Bradford is an ethnically diverse city with high levels of socioeconomic deprivation. This study was undertaken to determine the causes for the excess of congenital anomalies seen in babies born in Bradford. The Born in Bradford study is an ongoing prospective birth cohort study of 12,453 women with 13,776 pregnancies recruited in 2007 to 2011. Data included information on demographics, clinical outcomes, and risk factors, which included ethnic origin (white British, Pakistani, other), maternal age (<20, 20–34, ≥34 y), educational attainment, socioeconomic status, smoking, alcohol consumption, and consanguinity. Risks were calculated for all ethnic groups and separately for white British, Pakistani, and other groups. The population attributable risk was calculated for the offspring of first-cousin parents in the Pakistani community. Congenital anomalies were identified in 386 (3%) of 11,396 cases for whom questionnaire data were available. The national rate for congenital anomalies, excluding chromosomal disorders, was 165.90 per 10,000 live births compared with a rate of 305.74 per 10,000 live births in this study. Ethnic origins included 39% white British, 45% Pakistani, and 15% other (43 different ethnicities). Sixty percent of Pakistani babies had anomalies compared with 45% in the cohort overall. In the white British subgroup, significantly more babies with an anomaly were born to mothers 34 years or older than to those 20 years or younger to 34 years. Mothers with a higher level of education were less likely to have babies with an anomaly than were mothers of other educational levels. Maternal smoking, alcohol consumption, and obesity were not risk factors for congenital anomalies. For 18% of mothers, their partners were their first cousins. Fewer than 1% of babies of white British origin were the offspring of first-cousin unions compared with 38% of those in the Pakistani subgroup and 5% of those in the other subgroup. Anomalies were present in 6% of offspring of first-cousin unions and 5% of those of more distantly related parents. Mothers in first-cousin unions were more than twice as likely to have a baby with an anomaly than were mothers in nonconsanguineous unions; rates for nonconsanguineous unions did not differ significantly among ethnic groups. No significant effect was seen for the interaction between deprivation and consanguinity on risk of congenital anomaly (interaction RR, 0.99; 95% confidence interval, 0.97–1.01). For the offspring of first-cousin parents in the Pakistani population, the population attributable risk was 30.7%, and the RR was 2.18. These results indicate that consanguinity is a major risk factor for congenital anomalies. Antenatal counseling covers the risks associated with advanced maternal age, medications, and alcohol consumption, but should also include advice about the risks associated with consanguinity. Culturally sensitive information about the risks of consanguineous unions and congenital anomalies should be available and communicated to couples and local communities. Health professionals should be aware of the increased risks because these risks will result in an increased need for antenatal, pediatric, and genetic services.