Does the dawn phenomenon have clinical relevance in normal pregnancy?

OBJECTIVE: The dawn phenomenon is a transient rise in blood glucose between 4 and 6 AM that is attributed to the pulsatile release of pituitary growth hormone (GH). In pregnancy, GH is suppressed by placental GH. Hence, we hypothesize that there is no evidence for the dawn phenomenon in late pregnancy in healthy women. STUDY DESIGN: Twenty glucose-tolerant women with singleton gestations between 28 weeks and 36 weeks 6 days' gestation were recruited. The women were admitted overnight to the Clinical Research Unit and had continuous glucose monitoring. Insulin and GH were measured at 2-hour intervals from 8 PM to 8 AM. GH was grouped into times 1A (8-10 PM), 2A (12-2 AM), and 3A (4-8 AM) for changes over time. Further analysis was performed with time 1B (8 PM to 2 AM) and 2B (4-8 AM). Insulin was measured between 4 and 8 AM. RESULTS: Plasma glucose decreased over time (P < .001). There were no significant changes in GH among times 1A, 2A, and 3A (P = .45) or times 1B and 2B (P = .12). Insulin concentrations increased after meals, but there were no changes from 4 AM (8.5 +/- 1.4 mu U/mL) through 8 AM (8.6 +/- 1.1 mu U/mL; P = .98). CONCLUSION: Glucose and insulin concentrations show no increase from 4-8 AM; although there is variability in GH, there is no evidence for the dawn phenomenon in late pregnancy in healthy women.