The hormonal trajectory along gestational age: Cortisol and oxytocin levels profiles.

Pregnancy is accompanied by hormonal fluctuation, including increased cortisol and oxytocin (OT). Although the implications of these hormones during pregnancy are extensively studied, their normative variability is not well established. Therefore, we evaluated how serum cortisol and OT levels behave throughout pregnancy. This longitudinal study is part of a population-based cohort of pregnant women living in a city in Southern Brazil. Pregnant women up to 24 gestational weeks were evaluated at the time of identification (1st wave, N=983) and 60 days after the initial interview (2nd wave, N=840). At both times, blood samples were collected for hormonal dosage. We investigated the trajectory of these hormones throughout pregnancy using growth curve modeling. The best-fitting model was the exponential growth model, in which the variance explains approximately 79.1 % of the outcome. Thus, the cortisol level was, on average, at 44.2 μg/dl (95 %CI: 29.2;59.1, p<0.001) in the first gestational week, with an increase of approximately 2.0 % (95 %CI: 1.01;1.02, p<0.001) each week. OT showed no significant changes. While cortisol appears to follow a trajectory of exponential increase, possibly in response to the demands of fetal development, the variation in OT levels throughout pregnancy still remains constant subject to further investigation.