Women are taking longer to give birth than they did 50 years ago, according to a paper in the American Journal of Obstetrics and Gynaecology. The research suggests that the length of labour has increased by 2.6 hours for first-time mothers and by two hours for women who have previously given birth. So should you believe this, and does it matter? If you are in labour and your midwife or obstetrician says you have fallen off the Friedman curve (a graph drawn by American obstetrician Emanuel Friedman showing the time it takes in an ideal labour for your cervix to fully open so you can push your baby out), should you admit defeat or wait because labour takes longer these days?

The solution

The first part of labour can take hours. During this time the cervix opens up slowly and painfully to 4cm. From then on the labour is considered "active", which according to the Friedman curve, means the cervix is meant to open up by at least 1cm an hour.

If the cervix doesn't progressively open after any two-hour period, then you have fallen off the Friedman curve and could be given oxytocin, a drug that makes contractions stronger and pushes labour along, or even a caesarean section if there are worries about the wellbeing of mother or baby. What this latest research says is that labour is taking longer than when Friedman drew his curve.

It is not completely clear why, because lots of things are different. "Women are older when they give birth, they weigh more and they are less active in labour – they stay in bed more instead of being more ambulatory as they were in the past," says Katherine Laughon, an obstetrician and author of this latest paper. "It used to take women 3.9 hours to go from a cervix that was 4cm to one that was fully dilated. Now it takes 6.5 hours. Almost all women would give birth within 18.5, now most do so within 24 hours."

Laughon's study compared data from about 40,000 women from 1959-66 with data from 98,000 women from 2002-08. Many more women these days have epidurals – which Laughon says increases labour by 40-90 minutes – but since it stops labour hurting, who cares? But this didn't explain all of the difference. She believes that proper active labour starts later, when the cervix is dilated to 6.5 to 7cm, and that doctors and midwives can wait longer before speeding things up.

In a previous paper, Laughon argued that caesarean section rates may be increasing because doctors leap in too early to diagnose a stalled labour (known medically as failure to progress), before it has even reached its active stage. There is no evidence that waiting is risky to the baby, but that may be because the studies are not large enough to detect a difference as bad outcomes are, thankfully, rare. So it is probably best to wait at least a little longer.