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Gestational Diabetes Mellitus

Pregnancy Dr Erin Nesbitt-Hawes Director
It is estimated that gestational diabetes can occur in 5-10% of pregnancies. During National Diabetes Week we look at how this disease may affect you…

Gestational diabetes mellitus (GDM) is a condition that occurs during pregnancy when a woman is unable to respond to the changing hormonal environment caused by the growing baby and placenta. As a result she has blood glucose levels which are elevated above normal. GDM differs from Type 1 or Type 2 diabetes in pregnancy as it is not a pre-existing condition, but one that develops over time. It is important for women with Type 1 and 2 diabetes to have good control of their blood glucose levels prior to pregnancy to help to avoid complications and this will be further dealt with in a later blog.

Testing for GDM occurs during pregnancy routinely at 26-28 weeks gestation. Women with risk factors (such as family or personal history of for GDM, age >40, history of polycystic ovarian syndrome, elevated BMI >35) will have more than one test, the first of which is performed at 12-16 weeks. Testing involves a glucose tolerance test which requires women to have a series of blood tests over a 2 hour period following drinking a specified glucose drink containing 75g of glucose. The initial blood test is performed fasting, then at one and two hours after drinking the glucose load. Women may be diagnosed with gestational diabetes if their fasting, 1 hour or 2 hour results are above normal. Previously, a screening test of 50g of glucose over 1 hour was performed however this was phased out as it was found to miss women with diabetes and required women to attend for a second full two hour test.

So, why do we test for GDM anyway? The main way that elevated blood glucose levels can affect the baby is to cause the baby to be larger than normal (macrosomia). This obviously has implications for the delivery of the baby (quite a daunting consideration for the women involved!). Babies of women with uncontrolled diabetes are more likely to have labour complications such as requirement for instrumental (forceps or vacuum) delivery, episiotomy, significant tears, shoulder dystocia (where the baby’s shoulders get stuck in the birth canal after delivery of the head) and caesarean delivery. Additionally, after the baby is born it is more likely to require transfer to the neonatal intensive care unit for blood sugar monitoring and assistance with breathing.

Close control of GDM with blood sugar levels in the normal range bring these risks back to average. For most women with GDM all that is required is a stricter diet (in conjunction with a diabetes educator, dietician and endocrinologist) and exercise. Some women require treatment for GDM in pregnancy and this may involve taking tablets or giving insulin injections. Monitoring of the baby is performed at more regular intervals and includes regular ultrasounds to measure the baby’s growth. Sometimes it is recommended that the baby is born prior to the due date to reduce the risks and this will be discussed with your obstetrician as the pregnancy progresses. This may require induction of labour or a planned caesarean delivery.

What happens after the pregnancy? The good news for most women is that blood glucose levels return to normal very quickly after the delivery of the baby and placenta. In subsequent pregnancies you are very likely to develop GDM again and will have an early test at 12-16 weeks. Women need to be re-tested for diabetes every 2-3 years after the pregnancy as if you have had GDM you are much more likely to develop type 2 diabetes later in life.

A diagnosis of GDM does not necessarily mean a complicated pregnancy if it is detected early enough and monitored closely. Speak to your Alana Obstetrician for more information relevant to your pregnancy.

For more information about diabetes please visit Diabetes Australia.