Ready for the big event? A simple test could make it easier to predict when a baby is due.

Estimates of when a woman will give birth can be off by weeks. But a test, usually given to women at high risk of giving birth prematurely, seems also to predict whether labour will begin within the next week in women who have reached full term.

The test uses an ultrasound probe to measure the length of the cervix. This shortens in the run-up to giving birth, and can be used to predict if a woman is likely to deliver within the next week. The technique works for women who are likely to give birth prematurely, but until now it has been unclear whether this approach would also be effective in women who have safely reached the nine-month mark. The thinking was that by this time, all women may have a shortened cervix, making this measure no longer a useful sign of impending labour, and five studies turned up mixed results.


Now a meta-analysis by Vincenzo Berghella of Thomas Jefferson University in Philadelphia, Pennsylvania, and colleagues has shown that the technique does still work after nine months, at least in normal cases where a woman is carrying only one baby, in the proper head-down position.

A woman’s cervix is normally 3 to 5 centimetres long. Their analysis found that, once it has shortened to 1 cm or less, a woman has more than an 85 per cent chance of giving birth within the next seven days. But as the due date approaches, if the cervix is still more than 3 cm, the likelihood of delivering within the next week is less than 40 per cent.

This approach might help doctors decide whether to induce labour because of concerns over a baby’s health, says Ronald Lamont of Northwick Park Hospital in London, who is also a spokesman for the Royal College of Obstetricians and Gynaecologists. If the cervix is still long, an induction would be less likely to succeed, so a Caesarean section might be a better option.

Journal reference: British Journal of Obstetrics and Gynaecology, DOI: 10.1111/1471-0528.13724, 2015

(Image: Westend61/Getty)