Many of us have heard stories from our parents and grandparents about how they had their vaginas examined during pregnancy and they were told if their baby would be able to fit through their pelvis. My own grandmother was never given the option of labouring because she was a slim woman and told the baby wouldn’t be able to come out!
Nowadays practice has changed a lot, but there is still some controversy about what to do when a baby is measuring larger than expected:
What is a big baby?
You will have your bump measured with a tape measure and plotted on a chart throughout pregnancy. This gives an indication of how your baby is growing compared to previous measurements as well as other babies you had, your ethnicity etc. If measurements are bigger than expected you will have a scan to check the size of your baby.
The main measurements to see are the size of the abdomen (AC) and estimated fetal weight (EFW). If these are outside normal ranges (above the 95th centile) you will have a discussion with a doctor.
What happens next?
To check why your baby might be big, we will check to see if you have diabetes or review your sugars if you already have it. The next step depends on where you are in pregnancy. If you are nearly term (over about 36 weeks) we can discuss delivery of the baby.
Why does it matter?
Big babies (over 4000g or 9lb) can suffer injures at birth. Inducing labour early, before the baby grows too big may reduce this trauma.
However, if done too early, induction can result in babies being born prematurely and with immature organs. Induction of labour before due dates may also increase the risk of C-section.
Finally, ultrasound is not very accurate at measuring a baby birth weight, so it may turn out that induction was unecessary if baby is born a normal size.
What do the guidelines say?
The last NICE guideline of induction of labour (2008) states that induction of labour should not be carried out only for the reason of large baby.
What is the latest evidence?
More recent studies may soon change practice. A Cochrane review was published in 2016 looked at 4 trials, including 1190 women. It showed that induction of labour at 37-40 weeks reduces the risk of fracture (by 1.6%) and shoulder dystocia (by 2.7%). It also reduces the baby’s weight at birth.
In this study, there was no difference in the rates of C-section and instrumental delivery.
The authors of the study suggest that in settings where obstetricians can be reasonably confident about their scan assessment of fetal weight, the advantages and disadvantages of induction at or near term for fetuses suspected of being macrosomic (EFW above 4000g) should be discussed with parents.
My own experience is that most clinicians take their own approach to this issue, and this may depend on the guidelines at each individual hospital. However, if your baby is measuring consistently above the 95th centile, it is reasonable to discuss your options for the timing and type of delivery that would be suitable for you.
Did you have a big baby? Did you have discussion about birth? I would love to hear about your own experiences!