CHANGES OF DIMERIC INHIBIN-B LEVELS IN MATERNAL SERUM THROUGHOUT HEALTHY GESTATION AND IN WOMEN WITH GESTATIONAL DISEASES

Human placenta expresses subunit messenger RNAs for synthesizing inhib in A and B. Experimental studies have shown an effect of inhibins on p lacental hormone secretion, but an endocrine function is suggested by the high levels in maternal circulation. Although information is avail able on the changes of inhibin A in serum of healthy pregnant women, d ata on inhibin B levels are limited to early gestation. The aim of the present study was to investigate the changes of inhibin B levels in m aternal circulation in healthy pregnant women throughout gestation, an d to evaluate whether early pregnancy disturbances or gestational dise ases are characterized by abnormal inhibin B levels. The protocol incl uded various groups of pregnant women. A longitudinal evaluation of se rum inhibin B levels was done at specific intervals (8-12, 13-18, 19-2 4, 25-28, 29-33, and 34-40 weeks) in the following groups: 1) healthy pregnant women (n = 13); 2) women at risk of hypertension who did not develop hypertension (n = 8); and 3) women with chronic hypertension ( n = 13). In women in group 1, a blood sample was also obtained in the postpartum period (12, 24, and 48 h after delivery). Other pregnant wo men with abnormal bleeding in the first trimester were studied; they w ere subdivided into women with ongoing pregnancy (n = 12); and women w ith miscarriage (n = 22); a control group of healthy pregnant women at the same gestational age was also included (n = 18). A final group of women with gestational diseases (n = 34) was included in the study an d included women with: 1) pregnancy-induced hypertension (n = 10); 2) preeclampsia (n = 17); and 3) intrauterine fetal growth retardation (n = 7). A group of healthy nonpregnant women (n = 9) was used as contro ls, and a blood specimen was collected during both the early-to midfol licular and midluteal phases of the menstrual cycle. Serum dimeric inh ibin B levels were measured by using a double-antibody enzyme-linked i mmunoadsorbent assay. Early gestation inhibin B levels were similar to those of nonpregnant controls and showed a significant rise during th e third trimester (P < 0.01). The highest maternal serum inhibin B lev els were found at term (P < 0.01). Values significantly returned to co ntrol levels within 12-48 h (P < 0.01) after placental delivery. Women at risk of hypertension showed a similar gestational-related increase of inhibin B levels during the third trimester, without any significa nt difference when compared with healthy women. Women with chronic hyp er tension showed significantly lower levels at term (P < 0.01). Women with pregnancy-induced hypertension or preeclampsia, or who were carr ying a fetus with intrauterine growth retardation showed serum inhibin B levels during the third trimester of gestation consistently lower t han in control healthy women at the same gestational age (P < 0.001, m ean +/- SEM). Maternal serum inhibin B levels in women with early preg nancy bleeding or miscarriage were similar to those of healthy pregnan t women at the same gestational age, independent from the outcome of g estation. The present study showed that maternal serum inhibin B level s increase in the last trimester of normal pregnancy, with low levels in women with hypertensive disturbances or intrauterine growth retarda tion.