UNLABELLED: Pregnant women are normally screened for Gestational diabetes (GDM) at week 24 of pregnancy. However some women develop the disease later on their pregnancies. No study has analyzed women developing GDM later in pregnancy. OBJECTIVE: To analyze data on a cohort study and compare women diagnosed with GDM in second and third trimester of pregnancy with women without GDM. RESULTS: GDM women diagnosed during their first two trimesters of pregnancy were older (p = 0.0008) and had higher body mass index (BMI) (p = 0.0007) than non GDM women. However, the only risk factor in women diagnosed in their third trimester of pregnancy was having first degree relatives with type 2 DM and this was independent of age and BMI (OR of 2.7, 95% CI 1.2 - 6.0). CONCLUSIONS: Women who develop GDM in their second trimester of pregnancy have known risk factors for diabetes mellitus such as age and higher BMI, however, the only recognised risk factor between non GDM women and women developing GDM late in pregnancy is family history of type 2 DM. Two populations of GDM may exist and future studies should focus on analysing short and long term complications of these women to support the need to diagnosed and treat them all.