What is gestational diabetes?

Gestational diabetes is the type of diabetes that presents exclusively in pregnancy in women without a history of diabetes. During pregnancy the placenta produces hormones that promote fetal growth. These hormones increase insulin resistance. In some women the pancreas cannot deal with the pregnancy-related changes, thus they develop gestational diabetes.

How common is it?

Gestational diabetes is common. Almost 2 out of 10 women are going to develop gestational diabetes, usually after the second trimester of pregnancy.

Risk factors

You are at increased risk of developing gestational diabetes in the following situations:

  • Age above 35 yrs
  • Increased BMI≥30
  • History of increased insulin resistance
  • Polycystic ovarian syndrome
  • Increase birth weight ≥5 Kg
  • History of gestational diabetes in previous pregnancy
  • If you had a stillbirth in the past
  • Family history of diabetes
  • Excessive weight gain during pregnancy
  • Multiple gestation


  • 1st trimester
    Every woman needs to have a fasting blood sugar test in the 1st trimester of pregnancy. If the fasting blood sugar is >92 mg/dl, she is considered to have gestational diabetes (or preexisting diabetes depending on the fasting blood sugar level) and she needs to be reviewed by an endocrinologist.
  • 24-28 weeks of gestation
    The glucose tolerance test (GTT) is the blood glucose measurement at fasting and 1 and 2 hours after drinking 75 gr. of glucose. Before the GTT the pregnant woman needs to freely consume carbohydrates for at least 3 days prior the test. If even one of the blood sugar levels is above the normal limit, the woman is considered to have gestational diabetes.

How does gestational diabetes affect pregnancy?

Most women who develop gestational diabetes give birth to healthy babies. However, sometimes there might be serious complications, especially if the diagnosis is delayed or if the management is suboptimal.

If the blood sugar levels are too high, the fetus produces increased amount of insulin that increases the risk of fetal macrosomia (birth weight >4 Kg). This is related to complications at birth (shoulder dystocia and postpartum haemorrhage), increased risk of Caesarean Section and complications after birth (i.e. hypoglycaemia, respiratory distress). In some cases of poorly controlled diabetes there might be complications affecting the mother such as pre-eclampsia and preterm delivery.

Antenatal care in gestational diabetes

If you develop gestational diabetes you are going to be look after by a dedicated team consisting of your obstetrician, an endocrinologist and a dietician.

You need to check your fasting blood sugar every morning and 1 hour after every main meal. The sugar levels should be:

  • Fasting glucose levels 1 hour before breakfast <95 mg/dl
  • 1 hour after meal <135 mg/dl

The main interventions for gestational diabetes control are healthy diet combined with exercise. However, in some cases it might be necessary to start treatment with drugs or insulin.

Women with gestational diabetes need frequent ultrasound scans to monitor the fetal growth and amniotic fluid. Poorly controlled diabetes could cause fetal macrosomia and increased amniotic fluid.

Time of delivery

Ideally a woman who has gestational diabetes should deliver between 38-40 weeks of gestation if there are no complications.

Do you need to have a Caesarean Section?

If there are no other maternal or fetal factors, gestational diabetes alone is not an indication for Caesarean Section.

After the birth

Women who developed gestational diabetes need to monitor the blood sugar levels for 2-3 days after delivery.

The GTT needs to be repeated in 6-8 weeks after birth to confirm. If the results are normal, the blood sugar needs to be tested in 6 months and every year thereafter, as there is increased risk of developing type II diabetes in the future.