Babies born to South Asian women are at a higher risk of perinatal mortality (death before, during or shortly after birth) than babies born to black or white women, concludes a study published online by the BMJ today.
The World Health Organisation defines post-term pregnancy as beyond 41 completed weeks from the first day of the last menstrual period. Post-term pregnancy is associated with increased perinatal mortality, and induction of labour at 41 weeks is often used to help avoid this risk.
However, evidence shows that the average length of gestation varies between racial groups. For example, it is shorter in South Asian and black women, suggesting that complications may occur before the 41 week induction point in these women.
Researchers from London and Bristol tested this theory by studying whether the risks of post-term birth complications increased earlier during pregnancy in South Asian and black women compared with white women.
Their study involved over 197,000 white, South Asian and black women who were expecting their first child and who delivered a single baby weighing at least 500 grams at 24 to 43 weeks.
They found that the perinatal mortality patterns differed significantly with racial group. At every stage of gestation, perinatal mortality was highest in South Asian women, and from term onwards, the upswing in risk occurred earliest and steepest in South Asian women, then black women, followed by white women.
The authors say their findings indicate that there are genetic variations in gestational length and argue that increased foetal surveillance and growth monitoring from 40, rather than 41, weeks' gestation is needed for South Asian and black women.