There are many points of discussion around Gestational Diabetes (GDM):- how to diagnose it, when to use insulin but a thorny issue is the timing of the delivery. In the clinic I am sometimes asked “Do I have to be induced early?” I feel this is more an obstetrical than diabetes related decision and I work with obstetricians I trust but that does not mean the decision should not be questioned. Understanding the background knowledge can inform those questions.
First of all what are the things we worry about? The most terrifying word at this stage of pregnancy is “stillbirth” and it is sometimes raised as a reason for early delivery (See FAQ GDM). In a low risk population the risk of stillbirth is 1.6 per 1000 women (lowest in those who deliver from 38 to 41 weeks) so if asked by a pregnant woman “Can I have a stillbirth” my answer is “If you phrase the question that way there can only be one answer, yes. Can I be run over on the way home tonight – yes, will I be run over on the way home tonight – no. Do I think you will you have a stillbirth- No”. Years ago when severe cases of GDM were not being diagnosed and treated there probably was an increased risk but modern studies do not show this. A large population study from Israel published in 2011 found no increased risk of stillbirth in GDM, in fact GDM may even have a lower risk of stillbirth. A population study from Sweden in 2010 also found no increased risk of stillbirth in GDM. Thus, I do not think there is an increased risk of stillbirth in GDM. The other issue in GDM we worry about is the baby getting too big and then having a more difficult birth. As the pregnancy progresses the baby gets bigger so a 41 week baby will usually be larger than a 38 week baby. Thus, there is a concern of more large babies if the pregnancy is allowed to go on for longer.
In 2004 the American Diabetes Association suggested that “Prolongation of gestation past 38 weeks increases the risk of fetal macrosomia without reducing cesarean rates, so that delivery during the 38th week is recommended unless obstetric considerations dictate otherwise.” This was based on a 1993 study of a total of 200 women with the half induced at 38 weeks having less large babies than those allowed to go to 40 weeks. Thus the tradition has grown up that once GDM is present then delivery should be early. Ideally what is done is based on good evidence but there is not much in the way of good evidence in this area. So what is the best way forward?
I think GDM covers a spectrum of those with great glucose control with nutrition changes alone to those with difficult control despite lots of insulin. For diet controlled GDM with no other concerns delivery should be by the 40th week as suggested by Dr Cornelia Graves in her review in 2007. If a woman with GDM needs insulin or oral hypoglycemic agents and assuming all else is fine, then an ultra sound at 37-38 weeks can help (accepting that ultrasounds are not as accurate at predicting the baby’s weight as we would like). The approach suggested by Dr Deborah Conway in 1998 makes sense to me: If the baby is less than 4000 grams it may be reasonable to watch until 40 weeks and deliver, if the estimated weight is over 4250 or the baby is large for gestational age then I would favor induction and a discussion about the mode of delivery and if between 4001 and 4250 grams then induction should be discussed. All involved want a healthy baby but should be on the same page. If the delivery planned for your baby is not what you would like then ask your care giver if there good evidence for what they want to do. I would hope they would be open to this discussion. The relationship has to have trust and there are times I get an uneasy feeling about a situation and just feel it is better deliver earlier than later. These grey areas are never easy but talking about them sheds light on the situation and should help.