Normal fasting plasma glucose levels during pregnancy: a hospital-based study

Recently, the International Association of Diabetes and Pregnancy Study Groups have suggested new criteria for the diagnosis of gestational diabetes including a fasting glucose level of ≥92 mg/dL. We determined reference levels for normal fasting plasma glucose levels throughout pregnancy and evaluated the new normal cut-off for fasting glucose level.

Charts of patients who delivered in our hospital between June 2001 and June 2006 were reviewed. Women with pregestational diabetes, fasting glucose level >105 mg/dL or delivery at <24 weeks were excluded. Fasting glucose levels were assessed in 11 time categories between three months prior and four months postpartum in 7946 women.

Compared to preconception levels, fasting glucose levels decreased by a median of 3 mg/dL in the first trimester (81-78 mg/dL). During the third trimester a slight further glucose reduction was observed (median 76 mg/dL). After delivery fasting glucose levels increased sharply (84 mg/dL in the puerperium and 81 mg/dL by three months postpartum). Throughout pregnancy 5.2-9.0% of pregnant women had a fasting glucose level of ≥92 mg/dL [compared to 8.2% in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study].

Fasting glucose levels decrease early in pregnancy with only slight further decrease later on. It seems that the same fasting glucose cut-off can be used throughout pregnancy for the diagnosis of gestational diabetes mellitus.