Las mujeres negras tienen más probabilidades de experimentar un mortinato que las mujeres blancas

The largest study of its kind, published in the PLOS Medicine journal, saw an analysis of over 15 million pregnancies across 13 studies in the UK, USA, Denmark and Norway, led by Queen Mary University of London.

They found a small but significant increase in risk for stillbirth for all mothers whose pregnancies continued beyond 40 weeks. However, researchers assure women who are 41 weeks pregnant that they should not be alarmed as the risk is still low - one more stillbirth for every 1,449 pregnancies compared to delivering at 40 weeks.

However, for black women, the risk of stillbirth was one and a half to two times higher at all stages of pregnancy. Although the study did not look into causes, the potential reasons cited for the stillborn race gap included "low educational and socio-economic status, reduced access to antenatal care, and increased rates of fetal growth restriction". A different study had also found that the rate of maternal mortality (death in pregnancy and childbirth) was five times higher for black women than white.

Of the more than 3,000 stillborn babies each year in the UK, a third are babies carried for 37 weeks or more and considered healthy prior to death. The research showed that despite an increased risk of stillbirth for delivery past 40 weeks, the risk of newborn death (within the first 28 days of life) was unchanged between 38 and 41 weeks of pregnancy. However, the risk increased by 87% for delivery at 42 weeks compared with delivery at 41 weeks.

Lead researcher, Professor Shakila Thangaratinam from Queen Mary's Blizard Institute, commented: "We were surprised to see how much poorer pregnancy outcomes were for black women - they were up to twice more likely to experience stillbirth than white women. Healthcare professionals need to take these added risks into account when developing care plans for these women."

The researchers hope this study can be used to help women to make more informed decisions about induction and carrying a pregnancy past 40 weeks.

Dr Alexander Heazell, senior clinical lecturer in obstetrics at the University of Manchester, recognises that the research is an important piece of work "which confirms current knowledge that the risk of stillbirth is increased in pregnancies which continue after 41 weeks of pregnancy and at all stages of pregnancy in women of black ethnic origin. This association is biologically plausible as the placenta ages as pregnancy continues so by the end of pregnancy it is less able to deliver the oxygen and nutrients needed to sustain a baby".

This study was published in PLOS Medicine.