Cohort
This is a retrospective longitudinal study of 424 GDM pregnancy pairs, conducted in two centres: the Royal Hospital for Women (RHW), a tertiary maternity hospital in Eastern Sydney, and Blacktown-Mount Druitt Hospital (BMDH), a hospital in Western Sydney with the highest annual number of births statewide. Women who attended GDM clinics from 2003-2015 with more than one GDM pregnancy were identified. Each pregnancy pair comprised two consecutive singleton GDM pregnancies from the same woman (“index“ and “subsequent” pregnancies). In women with more than two GDM pregnancies, each set of consecutive GDM pregnancies was considered a pregnancy pair- e.g. in a woman with three GDM pregnancies, the first and second pregnancy and the second and third pregnancy were each considered as pregnancy pairs.
Both centres used the Australasian Diabetes in Pregnancy Society diagnostic criteria at the time of a fasting plasma glucose ≥5.5 mmol/L and/or a 2-hour glucose ≥8.0 mmol/L on the 2-hour 75 g oral glucose tolerance test (GTT), which was performed in women with a 1-hour plasma glucose of ≥7.8 mmol/L after a non-fasting glucose challenge at 24-28 weeks gestation. Screening for GDM was performed in the early second trimester in women with a history of GDM in a prior pregnancy, polycystic ovarian syndrome, BMI 35 kg/m2, maternal age 40 years or a first-degree relative with type 2 diabetes, and repeated at 24-28 weeks if GDM was diagnosed at that stage.
Glucose targets were a fasting glucose of ≤5.0 mmol/L and a 2-hour glucose of ≤7.0 mmol/L at the RHW, and a fasting glucose of ≤5.5 mmol/L and a 2-hour glucose of ≤7.0 mmol/L at BMDH. Women were referred to the diabetes educator, instructed on home blood glucose monitoring and a low glycemic index diet and encouraged to do 30 minutes of exercise per day. They attended one- to four- weekly appointments at the GDM clinic attended by endocrine doctors. Insulin was commenced in women who did not regularly meet their blood glucose targets. The diagnostic criteria, glucose targets and the principles of management of GDM remained consistent during the study period at both centres.