Lack of evidence for a circadian rhythm of IGFBP-1 in the mother and fetus during labour.

OBJECTIVE: To determine whether the circadian rhythm of circulating levels of insulin-like growth factor binding protein-1 (IGFBP-1) is evident at the time of delivery. DESIGN: Prospective observational study in six pregnant women and cross-sectional study in 65 women at the time of delivery. SUBJECTS: Six pregnant women sampled over a period of 24 hours, 23 women sampled at the time of elective caesarean section, and 42 women sampled at the time of vaginal delivery. RESULTS: In the women sampled serially over a 24 hour period there was an obvious circadian rhythm of IGFBP-1 with a peak between 01.00 and 09.00 hours. In the women sampled at the time of delivery there was no evidence for any relationship between the time of delivery and maternal or fetal levels of IGFBP-1. CONCLUSIONS: The circadian rhythm of IGFBP-1 is not observed in women in labour. Therefore, the time of day is not an important confounding variable in studies on IGFBP-1 levels at the time of normal delivery.