Cortisol rise during pregnancy is connected with fetal maturation. Together with the increase of insulin resistance it might have a role in allocation of nutrients between mother and fetus. Cortisol and insulin secretion during pregnancy seems to be induced by fluctuations in BMR. Here, we try to identify relationship between BMR and secretion of cortisol and insulin during pregnancy.
In 25 healthy women (age range 2039 years; mean±S.D., 28.6±4.4 kg/m2) body weight (BW), body mass index (BMI), BMR, basal insulin, and cortisol were measured in gestational weeks 12, 26 and 36. Homeostatic model index (RHOMA) and individual differences (Δ) between values at 36 and 12 week of gestation for each variable were calculated. We used a ventilated hood system (Deltatrac Metabolic Monitor; Datex Instrumentarium Corp., Helsinki) to measure CO2 and oxygen consumption during 20 min period. Insulin and cortisol were measured by RIA method. In statistical assessment repeated measures analysis of variance and Pearson product moment were used.
Both BMI and BMR significantly rose with advancing of pregnancy (P<0.001 for both). Cortisol increased from 396.9±173.2 nmol/l at gestational week 12, to 775.1±354.1 nmol/l and 800.0±285.0 nmol/l at gestational weeks 26 and 36, respectively (P<0.001, for both). Similarly, insulin secretion was augmented (from 7.9±3.0 mIU/l to 9.1±3.9 mIU/l and 11.7±5.4 mIU/l; P=0.001). RHOMA index rose, but this was less pronounced (P=0.042). We also found close positive correlation between ΔBMR with ΔBMI (r=0.47, P=0.008), Δinsulin (r=0.40, P=0.038) and Δcortisol (r=−0.42, P=0.03).
The rise of maternal serum cortisol and insulin suggest the activation of hypothalamo-pituitaryadrenal axis. Negative relationship between the increase of cortisol and BMR reflects cortisol induced decrease of fetal metabolic rate in late pregnancy. These may suggest brain involvement in control of energy homeostasis during pregnancy.