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Claire McLintock - Haematologist & Obstetric Physician

Private Service, Haematology, Maternity, Obstetrics and Gynaecology

Gestational Diabetes and Pre-existing Type 1 and Type 2 Diabetes

Gestational diabetes (GDM) is a type of diabetes that occurs in some women during pregnancy. Women with gestational diabetes have a high level of glucose (or sugar) in their blood because they do not produce enough of the hormone insulin to help process dietary carbohydrates they become more resistant to the effect of insulin as pregnancy progresses. Risk factors for GDM include being overweight, a family history of diabetes, a previous history of GDM, maternal age >35 years, women of Pacific Island, Indian, Asian or  Māori ethnicity. Women with GDM and pre-existing type 1 and type 2 diabetes are at increased risk of developing pregnancy complications including hypertensive complications of pregnancy such as preeclampsia, preterm delivery, macrosomic infants (babies >4500g).   

All women should be screened for GDM in pregnancy. This is usually done at around 26-28 weeks gestation but in women at high risk it should be done earlier in pregnancy. 

All women who develop GDM should have a glucose tolerance test done at their 6 week postpartum check. Women who develop GDM have an increased risk of developing type 2 diabetes in the long term and should receive regular screening by their family doctor. 

In many cases, gestational diabetes is managed by diet and exercise but many women require oral medications or insulin to keep blood sugar levels controlled. 

Good control of blood sugar levels before conception is very important in women with pre-existing type 1 or type 2 diabetes as uncontrolled diabetes is associated with an increased risk of congenital anomalies.

This page was last updated at 12:47PM on March 8, 2021.