Dangers of birth before 38 weeks

Too early?

AIMS Journal, Winter 1999/2000, Vol 11 No 4

A review of babies in the Northern Region born at 34 weeks or more who needed ventilation for respiratory distress syndrome, has shown what a huge difference a couple of extra weeks in the womb can make.

Since 1950 the WHO has defined births between 37 and 41 weeks as “term” but the authors suggest this has “clouded clear thought”. Their research show that one extra week in the womb makes a huge difference to risk of respiratory distress syndrome – and death.

When born at 34 weeks, 1 baby in 34 needed ventilation. At 35 weeks the risk was halved, to 1 in 73. At 36 weeks it was halved again, to 1 in 140. A 37 weeks it was 1 in 557, at 38 weeks it was 1 in 1692 and at 39-41 weeks it was 1 in 133,227.

When they looked at the reasons why some of the babies had been delivered by elective caesareans at 37-38 weeks instead of 39 weeks onwards, when their risk would be so much lower, the researchers found that some were done simply because the mother had had a previous section, or because the baby was breech. One was done for “fetal growth retardation” though in fact obstetricians had misdiagnosed the gestation – the baby was 34 instead of 38 weeks.

The authors conclude that elective section should be avoided before 39 weeks, unless labour starts spontaneously.

AIMS Comment

This valuable study is yet another example of how apparently scientific and clinical standards are set for convenience and “political” reasons although they may be both irrational and harmful. Originally immaturity was classified as a baby weighing less than 2,500 grams. However paediatricians realised that this was inadequate,(because babies can be small for dates) so they decided to define 37 weeks onwards as “term” pregnancies rather than classifying by the baby’s weight. No one checked whether 37 week babies were at risk of the hazards of pre-term birth. Because of this definition, obstetricians felt confident to deliver 37 week babies because they were called “term” – and mothers were told they were.

Women often call us to ask about dates of their planned caesareans. Our view is that if Nature designed a pregnancy to last around 283 days, there is a good reason for it.

  • Madar J, Richmond S and Hey E. Surfactant-deficient respiratory distress at “term”, Acta Paed, 1999; 88: 1244-8.