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 inhibin A and B. Experimental studies have shown an effect of inhibins on placental hormone secretion, but an endocrine function is suggested by the high levels in maternal circulation. Although information is available on the changes of inhibin A in serum of healthy pregnant women, data 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 maternal circulation in healthy pregnant women throughout gestation, and to evaluate whether early pregnancy disturbances or gestational diseases are characterized by abnormal inhibin B levels. The protocol included various groups of pregnant women. A longitudinal evaluation of serum inhibin B levels was done at specific intervals (8-12, 13-18, 19-24, 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 women with abnormal bleeding in the first trimester were studied; they were subdivided into women with ongoing pregnancy (n = 12); and women with 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 and 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 controls, and a blood specimen was collected during both the early- to midfollicular and midluteal phases of the menstrual cycle. Serum dimeric inhibin B levels were measured by using a double-antibody enzyme-linked immunoadsorbent assay. Early gestation inhibin B levels were similar to those of nonpregnant controls and showed a significant rise during the third trimester (P < 0.01). The highest maternal serum inhibin B levels were found at term (P < 0.01). Values significantly returned to control 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 significant difference when compared with healthy women. Women with chronic hypertension showed significantly lower levels at term (P < 0.01). Women with pregnancy-induced hypertension or preeclampsia, or who were carrying a fetus with intrauterine growth retardation showed serum inhibin B levels during the third trimester of gestation consistently lower than in control healthy women at the same gestational age (P < 0.001, mean +/- SEM). Maternal serum inhibin B levels in women with early pregnancy bleeding or miscarriage were similar to those of healthy pregnant women at the same gestational age, independent from the outcome of gestation. The present study showed that maternal serum inhibin B levels increase in the last trimester of normal pregnancy, with low levels in women with hypertensive disturbances or intrauterine growth retardation.