WASHINGTON (AFP) - Women in their first pregnancy should push early in the delivery, as soon as the cervix is fully dilated, in order to minimise risks to themselves and the baby, according to a study of 2,000 American mothers.

Several previous studies have had mixed or contradictory findings on the two most common techniques used in American maternity wards: pushing immediately or waiting about an hour in order to encourage spontaneous birth, which some doctors believe reduces the need for cesareans or forceps.

From May 2014 to December 2017, six American hospitals participated in a study to determine which method is the safest for mother and child.

Hospital staff advised half the women to push immediately after being fully dilated while recommending the others to wait an hour longer.

The 2,400 women who participated were randomly placed in either group. All had received an epidural or other pain relief.

In the study published on Tuesday (Oct 9) in the JAMA journal, the researchers concluded that pushing immediately reduced the risk of complications such as infections and haemorrhage for the mother, even if there was a greater risk of significant perineal tearing.

They also found that pushing as soon as the cervix is fully dilated didn't increase the number of C-sections, and the second stage of labour was half an hour shorter for those women.

As for the newborns, the risk of infection increased when women waited longer before pushing.

The study thus leaned more heavily towards recommending prompt pushing.

"Our findings suggest that women becoming mothers for the first time should begin pushing right away when they become completely dilated, for the best outcome for themselves and for their babies," lead author Alison Cahill, an obstetrician at Washington University in St Louis, told NPR radio.

The study, however, cannot be generalised to all pregnant women as it only concerned those giving birth for the first time following normal pregnancies and more than 37 weeks of gestation.

But it could help change practices at US maternity wards.