Prolactin, estriol and progesterone levels in frequent blood samples throughout normal pregnancy (lack of prolactin pulsatile secretion).

The aim of this paper was to study the episodic fluctuations of circulating prolactin (PRL), estriol (E3) and progesterone (P4) concentrations throughout pregnancy. We examined 24 pregnant women; 21 were between the 28th and 40th week of gestation, and the other 3 in the 12th, 16th and 20th week of gestation. Blood samples were drawn every 5 min for half an hour, and every 15 min for one and a half hour. Blood samples were taken in two and three different weeks of gestation in 11 and 2 of the cases, respectively. Two normal non-pregnant women were also studied and used as controls. PRL, E3 and P4 were determined by radioimmunoassay in all the samples. The coefficients of variation of PRL values were 40 and 22.6%, respectively, in the two control women, 8, 12 and 9.8% in the pregnant women studied at the 12th, 16th and 20th week of gestation, respectively, while in the 21 cases studied during the third trimester the coefficient of variation was 8 +/- 3% (mean +/- SD). The coefficients of variation of the values obtained for E3 and P4 in women studied in he third trimester were 26 +/- 15 and 16 +/- 6% (Mean +/- SD), respectively. There was an increase in the average concentration of the three hormones in all the cases at two or three different weeks. We can conclude that E3 and P4 have a pulsatile secretion pattern throughout pregnancy, and that PRL looses its pulsatile secretion as from an early gestational age. Our results suggested that central mechanisms regulating PRL episodic fluctuations were altered during pregnancy.