Time of day and glycaemic response in pregnant women: A gap in current guidelines?

Background & aims: Advice to monitor and distribute carbohydrate intake is a key recommendation for treatment of gestational diabetes, but fails to consider circadian regulation of glucose homeostasis. In the non-pregnant state, glucose responses to a meal at night-time are significantly higher than during the day and are associated with an increased risk of developing type 2 diabetes. However, the impact of night time eating on postprandial glucose in pregnancy is uncertain. Using a systematic approach we explored postprandial glucose responses to dietary intake at night compared to during the day in pregnant women. Methods: Searches were conducted in four databases (Ovid MEDLINE, Ovid Embase, CINAHL plus and Scopus), in September 2022 (updated, June 2023). Eligible studies reported on postprandial glucose at a minimum of two times a day, after identical meals or an oral glucose tolerance test, in pregnant women with or without gestational diabetes. Publication bias was assessed using the ROBINS-I tool. Results: Four eligible studies were retrieved. Two studies reported within group comparison of two timepoints, and observed reduced glucose tolerance in the afternoon compared to the morning in pregnant women, irrespective of diabetes status. The other two studies meeting inclusion criteria did not report time of day comparisons. Conclusion: It is unclear as to whether the higher (and extended) postprandial glucose levels observed at night in non-pregnant populations are observed in pregnancy. Clinical studies are needed to explore the impact of circadian rhythmicity on glucose metabolism during pregnancy, and the implications of current dietary advice on when and what to eat for management of gestational diabetes.