Myth: gestational diabetes means you’ll have a big baby


What is Gestational Diabetes Mellius?

The NHS states that “Gestational diabetes is high blood sugar (glucose) that develops during pregnancy and usually disappears after giving birth. It happens when your body cannot produce enough insulin – a hormone that helps control blood sugar levels – to meet your extra needs in pregnancy.”


The identification of gestational diabetes involves blood tests and an oral glucose tolerance test where you drink a high glucose drink to see how your body deals with the glucose. In the UK, women are told that treatment will reduce ‘serious health problems’, induction of labour, stillbirth, neonatal hypoglycaemia and injuries to the mother and baby (Royal College of Obstetricians and Gynaecologists, National Institute for Health and Care Excellence).

The gestational diabetes lottery


Thresholds for the identification of gestational diabetes mellitus (GDM) vary depending on where you are in the world (see the table below). These thresholds are narrower during pregnancy compared to if you were not, meaning if you are pregnant, you may be classed as diabetic, whereas you may not fit the criteria to be deemed diabetic if you weren’t pregnant.


Is treatment of gestational diabetes with drugs compulsory or always necessary?


No it’s not, and it’s important to understand the risks of not managing your blood sugar levels vs the risks of taking the medication to manage the diabetes. Treatment includes dietary management and drugs (tablets or insulin injections) to reduce blood sugar levels. There is an upward trend in managing gestational diabetes with drugs, yet it is not based on robust evidence and research.

The identification and treatment of gestational diabetes can affect your choices for birth place and method, as well as affect growth of your baby, so it’s vital you understand your options and decide how to manage your GDM.


“A 2018 Cochrane review concluded that the only likely treatment outcomes are fewer large babies, but at the cost of increased labour inductions, and with no proven benefit from adding pharmacology to lifestyle measures. Importantly, the birthweight reduction which occurs is mostly lean mass in normal-sized babies.
Neither insulin, oral hypoglycaemics, nor intense glucose control is shown to improve outcomes compared with diet and exercise alone, and a reduction in hypertensive disorders can reasonably be explained by weight control rather than glucose control.
Glucose levels short of frank diabetes do not increase perinatal mortality, nor does treatment reduce it. Treatment does not reduce injury to mothers or babies, forceps delivery, respiratory problems, or neonatal hypoglycaemia, and probably does not reduce caesarean section rates.”
The new gestational diabetes: Treatment, evidence and consent - Christopher K. Hegerty

So are all GDM pregnancy babies big?


No. They aren’t. And the management of GDM can reduce birth weight of all babies, including those who are small to start off with.

Reviews of millions of births show no significant increase in perinatal problems until birthweights exceed 4500 g (the top 2% of babies), but even if there is a benefit in reducing the growth of extremely large babies, the great majority of treated babies are not extremely large.
All treated babies have their growth and lean mass reduced, which may be detrimental, particularly as the majority are already of normal or small size. Nutrition and growth have advantages in the short and long term, and benefits may decrease with decreasing birthweight, so growth should be restricted only for clear reasons, particularly in normal or small babies.”
The new gestational diabetes: Treatment, evidence and consent - Christopher K. Hegerty

So is the treatment of GDM based on robust evidence?


Not necessarily. A Cochrane study states:

“No interventions to prevent GDM in 11 systematic reviewswere of clear benefit or harm. A combination of exercise and diet, supplementation with myo-inositol, supplementation with vitamin D and metformin were of possible benefit in reducing the risk of GDM, but further high-quality evidence is needed. Omega-3-fatty acid supplementation and universal screening for thyroid dysfunction did not alter the risk of GDM. There was insufficient high-quality evidence to establish the effect on the risk of GDM of diet or exercise alone, probiotics, vitamin D with calcium or other vitamins and minerals, interventions in pregnancy after a previous stillbirth, and different asthma management strategies in pregnancy. There is a lack of trials investigating the effect of interventions prior to or between pregnancies on risk of GDM.”
Griffith et al 2020

Of course, we need to be mindful of the potential risks that unmanaged gestational diabetes can pose for mother and baby, but these risks need to be weighed against the potential harm the management of suspected diabetes can cause.


If you’d like to read more about the management of gestational diabetes, and your options, I recommend the following articles, studies and resources:

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