The clinical significance of overt diabetes in pregnancy

To explore clinical implications of overt diabetes in pregnancy on antenatal characteristics, adverse neonatal outcome and diabetes risk post-partum.

Retrospective audit of prospectively collected data for all patients with gestational diabetes mellitus from 1993 to 2010. We defined overt diabetes in pregnancy as an HbA(1c) ≥ 8 mmol/mol (6.5%) or a fasting plasma glucose ≥ 7.0 mmol/l, or a 2-h glucose level ≥ 11.1 mmo/L on a 75-g oral glucose tolerance test as a surrogate for a random glucose ≥ 11.1 mmo/l.

Our audit identified 1579 women with gestational diabetes and 254 with overt diabetes in pregnancy. Women with overt diabetes in pregnancy were diagnosed earlier in pregnancy, had a higher number of risk factors for gestational diabetes, higher antenatal HbA(1c), fasting and 2-h glucose levels, higher pre-pregnancy BMI and higher insulin use and dosage requirements than those with gestational diabetes. Overt diabetes in pregnancy was associated with an increased rate of large-for-gestational-age infant, neonatal hypoglycaemia and shoulder dystocia. Of the 133 patients with overt diabetes in pregnancy who attended a follow-up oral glucose tolerance test at 6-8 weeks post-partum, 21% had diabetes, 37.6% had impaired fasting glucose or impaired glucose tolerance, whilst 41.4% returned to normal glucose tolerance.

In this patient cohort, overt diabetes in pregnancy significantly increased the risk of adverse pregnancy outcomes and post-partum impaired glucose regulation, but should not be regarded as synonymous with underlying diabetes. Two-hour glucose following a 75-g glucose load is a poor predictor of post-partum diabetes.