Aims This study aimed to determine the prevalence and relationships with known risk factors of gestational diabetes mellitus (GDM) at University College Hospital, Ibadan, Nigeria.

Methods Records of all women referred for oral glucose tolerance testing at the metabolic research unit of the Hospital over a 2 year period were reviewed. Diagnosis of GDM was made in accordance with WHO criteria. GDM diagnosis was classified as early and late based on a gestational age <24 weeks and >24 weeks respectively. Body mass index (BMI) measurements were performed for women who presented in the first trimester. Various statistical tools including student t test and Pearson's coefficient of correlation were used.

Results A total of 765 records were reviewed. The crude prevalence rate was 13.9%. The prevalence rate among women in the first trimester was highest at 17.4% although most of the diagnoses were made in the third trimester (55.7%). A positive family history and a family history of GDM were associated significantly with a higher fasting and 2 h post-load glucose values, irrespective of current GDM diagnosis. The most consistent associations with a diagnosis of GDM were a positive family history and a history of GDM. Age above 30 years at oral glucose testing also showed significant association. There was no BMI threshold associated with a significant risk of GDM for those women presenting in the first trimester.

Conclusions GDM is a common metabolic condition in Nigeria. Onset before the 24th week of pregnancy is not uncommon.