Prolonged Pregnancy: Induction

If you read a previous blog entry you know that due dates are not really that accurate, so it is considered normal to deliver anywhere between 37 weeks and 42 weeks from you LMP (Last Menstral Period).

I have wondered why, then, that in Idaho doctors do not like you going over your due date too long. In fact, at 41 weeks you are considered post-due and will be scheduled for an induction. I found some pretty interesting information.

Why would doctors want to induce labor after 41 weeks?

Many studies have been done looking at the outcome of pregnancies when the baby delivered at various gestations. After 42 to 43 weeks, there seems to be a consensus that there is more chance of problems for the baby. One of the indicators of how well a population's babies do is perinatal mortality. This is the ratio of stillbirths and early neonatal deaths per total livebirths and stillbirths. It is expressed 'per 1000 births'. In the UK the overall perinatal mortality rate (PNMR) is about 8 per 1000. Considering infants weighing 1.5 to 2.0 kg (3lb 4oz to 4lb 7oz), the PNMR of this group is about 75 per 1000.

After 42 weeks the PNMR doubles and after 43 weeks it has tripled. Many studies have looked into how we can monitor women after this time to try and pick out those that really do warrant induction, leaving the others to labour naturally. This has included surveillance techniques such as: kick charts, fetal heart monitoring, ultrasound scans to check for liquor volume, and 'doppler' assessment of blood flow in the cord. In summary, none of these is perfect, and even with intensive monitoring, such as a scan at 42 weeks, then twice weekly fetal heart monitoring, one baby in 1000 will die before it is born. The underlying problem here is that the placenta starts to show signs of 'ageing' as pregnancy progresses, and eventually doesn't work as well as it did previously.

These are the reasons why, in general, we recommend induction of labour around 42 weeks. Inducing labour before 41 weeks can lead to problems in labour. The cervix may not be ready to dilate and earlier induction does carry an increased risk of caesarean section for slow labour or 'failed' induction. After 41 weeks it is unlikely that induction of labour will alter the final mode of delivery.

What are My Chances of Going into Labour Naturally After 40 Weeks?

Actually, very good! The above-mentioned study in Nottingham found that, of women at 40 weeks, 65% labour spontaneously within the next week. Of those at 10 days over their dates, 60% will enter spontaneous labour within the next 3 days.

So it is worth trying to get induction as close as possible to 42 weeks, giving you every chance to labour spontaneously. Most obstetricians would not find this an unreasonable request if you find yourself in the antenatal clinic at 41 weeks!

(information above can be found in this article.)