Modified Glucose Tolerance Test (MGTT)

In general screening should be carried out for any pregnant women who have the following risk factors of GDM : 

1. BMI > 27kg/m²
2. h/o GDM in previous pregnancy
3. first degree relatives with DM
4. h/o macrosomic baby > 4kg
5. h/o baby with congenital anomaly
6. h/o unexplained IUD
7. glycosuria at first or any antenatal visit
8. current obstetric problems eg. PIH, pre-eclampsia, polyhydramion, steroid usage

Universal screening for gestational diabetes mellitus (GDM) should be performed between 24-28w using modified oral glucose tolerance test (MOGTT or MGTT).

However, initial screening of GDM in high risk women (h/o previous GDM) can be done at 16-18w. If the MGTT result is normal, the test is then repeated at 24w.

Steps for MGTT:

1. Mother is recommended to fast 12 hours before MGTT but 8 hours of fasting is also acceptable.
2. Maternal venous blood is drawn for fasting blood sugar level (FBS).
3.  A 75g of glucose in 250ml drink is given to patient and blood is drawn 2 hours later to determine the 2-hour post-prandial (2HPP) glucose level.

Normal value of MGTT :

• fasting < 6.1 mmol/L
• 2HPP <7.8

A single abnormal result is sufficient to make the diagnosis of GDM.