Gestational diabetes mellitus
Gestational diabetes mellitus (GDM), by definition, is any degree of glucose intolerance (high blood sugar) with onset or first recognition during pregnancy. GDM is the most common cause of diabetes during pregnancy, accounting for up to 90 % of pregnancies complicated by diabetes. Women with GDM have a 40–60 % chance of developing diabetes mellitus over the 5–10 years after pregnancy.
GDM affects roughly 7 % of pregnancies with an incidence of more than 200,000 cases per year. Pregnancy is a relatively short period marked by dramatic changes of hormone profile and body composition with profound effects on metabolism. There is no known specific cause, but it is believed that the hormones, produced during pregnancy, reduce receptivity to insulin, resulting in high blood sugar. While the initial phase of pregnancy is usually characterized by increased insulin sensitivity, later marked insulin resistance develops, which, in a subset of women with latent (underlying) defect of insulin secretion, manifests as a GDM.
Untreated gestational diabetes can damage the health of the foetus and the mother. The risks to the baby include macrosomia (high birth weight, Pic. 1), congenital (present at birth) cardiac and central nervous system anomalies, and skeletal muscle malformations. Increased fetal insulin may inhibit fetal surfactant (a fluid in the lungs, that lowers the surface tension of the lung alveoli) production and cause respiratory distress syndrome. Hyperbilirubinemia (high levels of bilirubin, the degradation product of haemoglobin, in blood) may result from red blood cell destruction. Untreated GDM can also result in stillbirth. Timely diagnosis of GDM should improve short-term pregnancy and perinatal outcomes.
Screening can be performed during the first prenatal visit, especially in mothers with risk factors (mentioned further in the text) for GDM. If the result is negative, or the test was not carried out during the first prenatal visit, screening at 24-28 weeks gestational age is ideal. Oral glucose tolerance test (OGTT) is accepted as a diagnostic “gold standard” for GDM diagnosis. Blood glucose level is measured 1 h and 2 h after glucose ingestion, fasting blood glucose is measured prior to the ingestion of the 75g glucose load. The OGTT should be performed in the morning after an overnight fast of at least 8 h. The diagnosis of GDM is made when any of the following plasma glucose values are met or exceeded:
After diagnosis, treatment starts with medical nutrition therapy, physical activity, and weight management, depending on pre-gestational weight. 70-85% of patients have good glycaemic control (normal blood sugar levels, Pic.2) with life style modification. Moderate amount of non-weight bearing exercise is an important adjunct to dietary advice. It is recommended that pregnant women exercise for about 20-30 minutes everyday/most days of the week. If lifestyle management and dietary changes fail to control the hyperglycaemia (high blood sugar), the next step is to initiate pharmacotherapy. Insulin is the drug of choice for the treatment of GDM.
Apart from cases associated with polycystic ovary syndrome, gestational diabetes does not directly reduce the patient’s fertility. However, gestational diabetes increases the chances of adverse pregnancy outcomes for the mother and the baby. The risk of stillbirth is also increased. However, most mothers with gestational diabetes have a healthy pregnancy.
The onset of gestational diabetes also means a higher risk of developing obesity and type 2 diabetes, with their specific adverse effects on health and fertility. The risk of developing type 2 diabetes depends on the severity of gestational diabetes and required therapy. Women requiring insulin to manage gestational diabetes have a 50% risk of developing diabetes within the next five years. Up to two third of women will re-experience gestational diabetes in future pregnancies. The risk of re-experiencing gestational diabetes also grows with the patient’s age, the number of pregnancies and the weight gained in between pregnancies.
The main diabetes type 2 complication related to pregnancy is (similarly to gestational diabetes) macrosomia - or a big baby (higher than the 90th percentile in birth weight). Sometimes these babies are not able to pass through the birth canal, so there are higher incidences of caesarean sections, and sometimes it is necessary to induce labor early. Fetal distress can also become an issue. There is also an increased risk of birth defects. This condition is directly related to maternal diabetes problems, especially during the first few weeks when a woman may be unaware she is pregnant. For this reason, women with diabetes are advised to manage their insulin levels under control before attempting to conceive.
In patients who manifest GDM, there is often improvement/complete resolution after delivery. However, GDM is an established lifelong risk factor for the development of diabetes in women with GDM history. Women with previous GDM had at least 7-fold increase of risk of developing type 2 diabetes mellitus (T2DM) in the future compared with those with normoglycaemia (normal blood sugar) during pregnancy.