Prematurity or immaturity?

Birth in the human is particularly difficult compared with that in the other primates. Bipedalism has evolved over the past 6 or 7 million years, and has resulted in a small pelvis, adapted to the upright posture. In recent millennia, the increasing size of the fetal head at birth has made childbirth difficult. Haig has suggested that the mother and fetus do not have identical interests; the baby benefits from being large at birth, while it is easier for the mother to deliver a small baby. Many of the 500 000 maternal deaths per year around the world are due to obstructed labour, especially in Africa. Even in London, black African women have the highest caesarean section rates. Black African babies are on average smaller than white European babies, due mainly to earlier delivery. In a 13-year study of births in North West Thames, African babies were 2.5 times more likely to be born between 24 and 31 weeks inclusive than white European babies. Between 33 and 38 weeks of gestation, black African babies behaved in a more mature way, are more likely to pass meconium and have jaundice, but less likely to have respiratory problems leading to admission to the special care baby unit. Preterm black African babies have lower gestation-specific perinatal mortality than white European babies, while at term and beyond the reverse is true. Preterm birth may have evolved partly as a response to disproportion.