The impact of timing of diagnosis of gestational diabetes mellitus on pregnancy outcomes

Abstract

Aim: To assess the impact on health outcomes in the mother and her infant when GDM is diagnosed at different gestational ages. Methods: Two systematic reviews compared pregnancy outcomes in women diagnosed with GDM at different times; the first compared earlier than recommended in New Zealand (< 24 weeks’ gestation) with current timing (≥ 24 weeks’ gestation); and the second compared within or close to the gestational age recommended (≥ 24 to 28 weeks’ gestation) with later diagnosis (> 28 weeks’ gestation). A cohort study, using contemporary New Zealand data from the TARGET randomised Trial, compared maternal and infant health outcomes when GDM was diagnosed as currently recommended (≥ 24 to 28 weeks’ completed gestation) with later diagnosis (≥ 29 weeks’ gestation). Findings: An increased requirement for oral hypoglycaemic and insulin for glycaemic control, decreased maternal weight gain during pregnancy, and increased perinatal mortality was found when GDM was diagnosed at < 24 weeks’ gestation compared with later. When GDM was diagnosed ≥ 24 to 28 completed weeks’ gestation compared with later, there was a reduction in the risk of pre-eclampsia, fewer vaginal births, an increase in insulin use for glycaemic control and an increased risk of neonatal respiratory distress syndrome. In the cohort study, women diagnosed with GDM in the Early Diagnosis Group compared with the Late Diagnosis Group were more likely to need pharmacological therapy (Relative Risk (RR) 0.84, 95% Confidence Interval (CI) 0.71, 0.99, P = 0.03) particularly insulin (RR 0.66, 95% CI 0.52,0.84, P < 0.001), infant birth weight was lower (mean, 3311 vs 3451 gm, p < 0.001 z score 0.15; p=0.02), and risk of infant death or serious morbidities trended lower (1.18% versus 2.89%, RR 2.45, 95% CI 0.98, 6.11, P = 0.06). Conclusions: Women where GDM was diagnosed earlier were more likely to need pharmacological therapy for glycaemic control and the current available evidence on health outcomes suggest some short-term benefits but also harms. The optimal timing for diagnosis of GDM needs assessment by high quality randomised trials that should report on all relevant maternal, fetal and infant outcomes.