An increasing number of births are planned, either by inducing labour or by planned caesarean. Giving birth early carries long-term as well as short-term risks. The final weeks of pregnancy are crucial for optimal brain development (the brain weighs two-thirds at 34 weeks of what it will weigh at 40 weeks). It is in the final weeks of development that many finer brain networks linked to developmental outcome are formed. A growing body of evidence points to long-term developmental delay by the time induced premature children reach school. Additionally, every week a baby is born prior to 39 weeks increases the likelihood of the need for breathing support and admission to newborn intensive care. This is important as these babies occupy scarce resources that could be avoided if birth could be safely delayed by a week.
In Australia, since the 1990s there has been a major change in birth practices that has resulted in a silent but steady shift towards women giving birth before 40 weeks. In New South Wales, for example, in the mid 90s a woman was most likely to deliver at 40 weeks. In 2016, between 38 and 39 weeks is the most common. During that time there was a year-on-year increase in the number of births between 34 to 39 weeks to the point where nearly one in five of all single babies born was at 38 weeks, one in 15 at 37 weeks and one in 40 at 36 weeks.
For every week a child is born earlier than 39 weeks there is a small but significant increase in the likelihood of them being developmentally vulnerable. Australian kindergarten children born after a planned birth scored poorly on two or more of these categories: physical health and well-being, social competence, emotional maturity, language and cognitive skills, communication skills and general knowledge. These are associated with longer term health, education and social outcomes. The risk was higher for babies born after a planned birth compared with spontaneous birth.