Gestational diabetes mellitus (GDM) is defined as glucose intolerance that begins or is first detected during pregnancy. GDM affects 3-8% of pregnant women and recognized as a risk factor for adverse perinatal outcome and associated with the later development of type 2 diabetes mellitus (DM).

Pregnancy serves as a metabolic stress test and uncovers underlying insulin resistance and â cell dysfunction. Placental secretion of hormones, such as cortisol, prolactin, and growth hormone is a major contributor to the insulin-resistant state in pregnancy. Insulin resistance usually begins in the second trimester and progresses throughout the remainder of the pregnancy. Women with GDM have a greater severity of insulin resistance and impairment of the compensatory increase in insulin secretion compared to normal pregnant women.

The WHO diagnostic criteria to diagnose GDM are based on a 2-hour 75 gram oral glucose tolerance test (OGTT). GDM is diagnosed if either the fasting glucose is more than 126 mg/dL or the 2-hour glucose is  more than 140 mg/dL.

Instructions for OGTT are as follow:

- eat as usual for 3 days before OGTT

- exercise as usual

- fasting for 10-12 hours

- check blood fasting glucose

- drink liquid contain sugar (75 gram sugar in 250 ml water) for 5

   minutes

- check blood glucose 2 hours afterwards

- during 2 hours of waiting, patient should take a rest and is not allowed

   to eat or  smoke

Fetal complications associated with GDM include macrosomia (birth weight > 4 kg), neonatal hypoglycemia, perinatal mortality, congenital malformation, hyperbilirubinemia, hypocalcaemia, and respiratory distress syndrome. Maternal complications associated with GDM include hypertension, preeclampsia, and an increased risk of cesarean delivery due to excess fetal growth (macrosomia).

Pregnant women should be screened for risk factors for GDM at their initial antenatal visit which include marked obesity, personal history of GDM, glucose intolerance, or glycosuria, or a strong family history of type 2 DM. If a woman is high risk, OGTT should be done as soon as possible. If the initial testing is negative, she should be retested between 24-28 weeks of gestation. If a woman is intermediate risk to develop GDM, she should undergo OGTT at 24-28 weeks of pregnancy.

Blood glucose monitoring is very important in GDM which goal is to maintain fasting glucose less than 95 mg/dL and 2-hour postprandial glucose less than 120 mg/dL. Controlling blood glucose with Medical Nutrition Therapy is the main GDM treatment. When nutrition therapy fails to maintain blood glucose levels at the desired ranges or when there is evidence of excessive fetal growth, insulin therapy is used. Oral hypoglycemic agents are not recommended for the treatment of GDM.

Postpartum management of women with GDM is critical. Maternal glycemic status should be monitored 6 weeks or more after pregnancy ends and every 3 years thereafter since their markedly increased risk of type 2 DM in the future.

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