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Birth: the importance of being on time

By Hanan El Marroun

Some babies are born four weeks too early and others are born three weeks past the due date. Their timing seems random, but that is certainly not the case. Of all births, around 90% take place between 37 and 40 weeks. There are several theories about how the timing of birth is regulated, but the process is not completely understood. According to one theory, the placenta runs on a nine-month clock, telling time by the flux of pregnancy hormones. Your clock may run fast, causing an early birth, or slow, bringing a late baby. According to another theory, the fetal brain acts like a computer, recording its own growth and environmental changes in the uterus until the moment for birth is just right.

Up to a few years ago, there was little expectant management in the Netherlands. Many midwives had the belief that childbirth should come naturally, relying on the mantra that “baby knows best”. Babies who spend extra time in the womb continue to grow and develop undisturbed by the outside world, so it was thought. This belief, long challenged by obstetricians, is commonplace on the Internet. The US group Ten Month Mamas advocates on their Facebook site that labor should not be induced even if pregnancy is post-term.

However, being born post-term can give rise to complications. Children born late are generally larger, and more often need a Caesarian section or an assisted delivery. Studies have shown that post-term births are associated with neonatal morbidity and mortality. Much less is known about the long-term consequences of post-term birth.
In the study that we recently undertook we were, therefore, interested in studying the relation between post-term birth and the child’s development. We followed more than 5,000 children born between 2002 and 2006 from early pregnancy onwards until age 3 years. In the early 2000s ultrasound examinations during pregnancy were not part of the diagnostic routine assessments in the Netherlands. However, as part of the study, mothers were offered three ultrasound examinations.

These ultrasound examinations were later used to calculate gestational age (time between conception and birth) of the newborn. When the children grew up, mothers and fathers each reported about their child at the age of 1,5 and 3 years. We were particularly interested whether being born post-term increased the risk of attention-deficit hyperactivity (ADHD), affective and pervasive developmental (autistic like) problems.

We observed a U-shaped association between gestational age at birth and emotional and behavioral problems. This means that not only a preterm birth but that a post-term birth increases the risk of problems in preschool children. Post-term birth predicted in particular the onset of ADHD-type problems, which were twice as likely to occur in children born after 42 weeks than in those born between 38 and 41 weeks.
Interestingly, the emotional and behavioral problems were not due to birth complications, such as assisted deliveries or high birth weight (>4000 grams).

So, how can this be explained? Possibly, a prolonged pregnancy is harmful for the child’s brain. Perhaps, the placenta ages and functions less well. In this case, inducing labor is indeed an effective way to prevent problems. On the other hand, post-term birth could indicate that the fetal brain or the placental clock was already disturbed. Then, the prolonged pregnancy is not the cause but one of the symptoms of a developmental problem already present early in life.

Since the beginning of the study, the expectant management policy in the Netherlands has been adapted to reduce the occurrence of birth complications. Like in all other developed countries, today a pregnant woman is referred to the gynecologist for close monitoring at 41 weeks and Caesarean section at 42 weeks of gestation. Whether the current policy reduces emotional and behavioral problems will be hard to prove, but this policy will certainly prevent many birth complications.

The International Journal of Epidemiology has granted free access to the full paper on this topic, “Post-term birth and the risk of behavioural and emotional problems in early childhood“, which is co-authored by Hanan El Marroun.

Hanan El Marroun is a postdoctoral researcher at the Erasmus MC – Sophia Children’s Hospital in Rotterdam, the Netherlands. She is very much interested in answering the question of how the intrauterine environment influences child development. Her current research is focused on the early and late effects of prenatal cannabis and tobacco use, and prenatal exposure to depression and antidepressants.

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