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.