Food for Thought

Why blood glucose levels matter in pregnancy.   
Prof Jennie Brand-Miller and colleagues Dr Kate Marsh and Prof Robert Moses have just published a book called The Bump to Baby Diet – a low GI eating plan for conception, pregnancy and beyond to share the latest science and help women enjoy a healthy pregnancy while safeguarding their baby’s future wellbeing. It’s available from bookshops and online in Australia and NZ and as an eBook from Amazon, iTunes etc. Here is an edited extract reproduced with permission of the publisher, Hachette Australia.

‘If you are pregnant or planning a pregnancy, reducing the GI of your diet is one of the safest and most effective ways of ensuring that your baby grows at the optimum rate, without laying down excessive body fat. Here’s why.

Pregnancy is a stage in life when carbs play a starring role. This is because a Mum’s average blood glucose level throughout the day is directly correlated with her baby’s growth rate in the womb. Quite simply, glucose is the primary fuel that drives all aspects of her baby’s development. If her glucose levels are too high, then her baby will grow too fast and be born with excessive amounts of body fat. This is not a new finding. It’s the main reason why women who have type 1 diabetes are given close medical attention before and during their pregnancies. It’s also the principal reason why all pregnant women are routinely screened at 26–28 weeks of pregnancy to determine if they have developed gestational diabetes. What’s new is that we now know that even mildly elevated glucose levels during pregnancy can have serious consequences.

Even if Mum is healthy and well, if her BGLs tend to be on the high side, baby will grow rapidly, and become too big for its own good. An overly large baby is linked to greater risk of delivery complications for both mother and baby. These infants have an increased risk of childhood obesity, as well as higher risk of metabolic diseases such as diabetes and hypertension in adulthood. Conversely, if her glucose levels are too low, baby’s growth might be too slow.

Pregnancy is a very real metabolic stress test for the body. It produces quite profound metabolic changes in all women. Even during the first trimester, her baby draws so much glucose from her blood stream that her fasting glucose levels and day-long levels are lower than they are in the non-pregnant state. Whether at rest or exercising, pregnant women use carbohydrate at a greater rate than do non-pregnant women. This is why one of the first metabolic adaptations the body makes to pregnancy is a greater capacity to produce glucose molecules in the liver. While this makes perfect sense (if access to food is temporarily restricted, the growing baby will still be getting the energy it needs), it means that all women become more and more insulin resistant as pregnancy progresses. For some women, this precipitates gestational diabetes.

Between the first and third trimesters, Mum’s insulin secretion in response to eating doubles, and her insulin resistance increases by about 50 per cent. This seems to be a normal physiological adaptation. Scientists believe that the higher degree of insulin resistance, particularly in the muscle mass, helps to redirect glucose away from Mum’s muscle cells towards her baby, enhancing its growth in the womb and health after birth.

Blood glucose levels in the baby always mirror those in the mother, with a difference of about 0.5 millimoles per litre (9 mg/dL) in Mum’s favour. Mum’s insulin cannot cross the placenta, but from about 12 weeks of age onwards, baby makes its own.

Insulin is often described as a ‘master hormone’, the conductor in charge of orchestrating many biochemical pathways in the body. In particular, we know it’s an anabolic hormone that stimulates growth and build-up of new tissues. Scientists believe that high blood glucose levels in the mother give rise to high levels in the placenta and umbilical cord blood, which in turn stimulates enlargement of the baby’s insulin-producing cells (called beta cells) and the secretion of excess insulin. It’s this extra dose of insulin that is the direct cause of above normal rates of growth.’

You can look inside The Bump to Baby Diet HERE.