Gestational age alters fetal breathing response to intravenous insulin and intravenous glucose administration.

An upward change in human maternal plasma glucose concentration is known to increase the percent of time spent in fetal breathing during the late third trimester of human pregnancy. We examined the fetal breathing effects of upward change in plasma glucose (after intravenous glucose administration) and downward change (after intravenous insulin administration) at two different times of day (8 AM and 4 PM) at both 24 and 36 weeks of gestation. No change in the percent of time spent in fetal breathing was seen after insulin infusion. Fetal breathing increased after glucose infusion at 36 weeks of gestation but not at 24 weeks. Responses did not differ between tests performed at 8 AM and 4 PM.