Background: Pregnancy is known to alter the feedback effect of cortisol on ACTH secretion and decrease the effectiveness of cortisol to inhibit an ACTH response to hypertension. Neither the mechanism nor the physiological significance of these changes in maternal plasma cortisol concentration is fully understood. This study is the first attempt to investigate the levels of serum cortisol during three stages of pregnancy and its associated physiological significance in Nigeria women. Aim: Serum cortisol in the three stages of pregnancy was measured and correlated with reproductive hormones and electrolyte levels. Methods: 200 volunteers consisted of 50 women in each of the three trimesters and 50 non-pregnant apparently healthy controls were recruited. Demographic data were obtained by questionnaire. Serum cortisol, progesterone and prolactin levels were measured by ELISA, chloride and bicarbonate by titration methods, Na+ and K+ by flame photometry and other analytes by conventional colorimetric methods. Results: While glucose and protein levels were significantly decreased, the total cholesterol concentrations increased progressively in pregnancy. Serum cortisol increased significantly in the first trimester reached a peak in the second and declined in the third trimester. Progesterone and prolactin levels were significantly higher in pregnancy in all stages of pregnancy. Serum cortisol correlates positively with chloride and potassium inversely with bicarbonate. Conclusion: Cortisol plays a central role in biochemical changes that occurs in pregnancy. It increase is an indicator of emotional stress and physiological challenges in pregnancy and also, possible risk signal. The concurrent increases in progesterone and prolactin levels are compensating mechanisms. It may therefore be of clinical relevance to monitor serum cortisol levels and some of the associated variables, especially in women experiencing threatened pregnancy.
Keywords: Cortisol, pregnancy, progesterone, prolactin, electrolytes