Serum levels of inhibin in maternal and umbilical blood during pregnancy

Serum and urine profiles of TGF-β superfamily members in reproductive aged women

BACKGROUND

TGF-β superfamily members are important biomarkers of reproductive health in women desiring fertility and during pregnancy. TGF-β proteins derived from the ovary and/or placenta have been detected in serum in women, but there have been very few attempts to measure them non-invasively, such as in urinary samples, and to compare them to serum concentrations.

METHODS

We measured inhibin A, inhibin B, total inhibin, AMH, activin A, activin B, activin AB, follistatin, the GDF-9/BMP-15 complex, and GDF-15 in paired serum and urine samples from healthy reproductive aged women and in pregnant (second trimester) women.

RESULTS

We detected all hormones in serum in both pregnant and non-pregnant women. Inhibin A, total inhibin, activin A, activin AB, follistatin, and GDF-15 were significantly higher in pregnant than in non-pregnant women. GDF-15 was the only hormone consistently detected in urine. We also measured, for the first time, the GDF-9/BMP-15 functional heterodimer and the GDF-15 protein harboring the H202D polymorphism.

CONCLUSIONS

We report the successful measurement of the GDF-9/BMP-15 heterodimer (its native form) in serum and the ability to measure GDF-15 non-invasively, in urinary samples. This novel GDF-15 assay also captures the antigen in the presence of a common genetic variant.

Inhibin-A levels between 14 and 20 weeks of gestation in Thai women

AIM

To construct a normal value for inhibin-A concentrations at 14-20 weeks of gestation for a Thai population.

MATERIAL AND METHODS

Inhibin-A concentrations from pregnant women without Down's syndrome at 14-20(+6) weeks of gestation were measured. Maternal serum inhibin-A levels were analyzed according to the gestational age.

RESULTS

Serum specimens from 727 Thai women were analyzed. Inhibin-A levels decreased from 14 to 17(+4) weeks and then gradually rose thereafter, giving a U-shape pattern.

CONCLUSION

The data of inhibin-A concentration at 14-20 weeks of gestation for normal Thai pregnant women fitted well with quadratic regression.

Inhibins as diagnostic markers in human reproduction

Over the past 75 years, many publications have focused on measurement of inhibin concentration and/or activity in biological samples in order to understand its role in physiology and disease. This chapter highlights the accomplishments within this area of research over the past decade including development of specific inhibin assays. Inhibin A is a marker of dominant follicle and corpus luteum activity and decreases in polycystic ovary syndrome (PCOS). Inhibin A increases in gestational diseases such as pre-eclampsia and fetal Down's syndrome, and this increase in inhibin A improves early diagnosis of both conditions. The measurement of inhibin A in women with threatened abortion provides useful information about the likelihood of pregnancy loss. Inhibin B increases markedly in women with granulosa cell tumor and appears closely related to gametogenesis in men, that is, reflecting Sertoli cell activity. On the contrary, Inhibin B decreases in women with declining ovarian function and correlates with female response to ovulation induction. This review evaluates the biochemical significance ofinhibins including their use in clinical practice.

Measurement of inhibin A and inhibin pro-αC in early human pregnancy and their role in the prediction of pregnancy outcome in patients with recurrent pregnancy loss

OBJECTIVE

To examine the temporal relationship among inhibin A, beta-hCG, and pro-alphaC in early pregnancy and to determine whether the measurement of these hormones has any role in prediction of pregnancy outcome in patients with recurrent spontaneous miscarriage.

DESIGN

Prospective descriptive study.

SETTING

A tertiary referral center for recurrent miscarriage.

PATIENT(S)

Thirty-six pregnant women with previous history of recurrent spontaneous pregnancy loss.

INTERVENTION(S)

Serial blood samples were collected prospectively at 6, 8, 10, and 12 weeks of gestation and were analyzed for inhibin A and inhibin pro-alphac using a two-site enzyme-linked immunosorbent assay as well as for beta-hCG using the microparticle enzyme immunoassay.

MAIN OUTCOME MEASURE(S)

Serum levels of inhibin A, inhibin pro-alphac, and beta-hCG.

RESULT(S)

The patients were allocated to two groups according to the pregnancy outcome: group 1 consisted of patients whose pregnancy continued beyond 20 weeks (control group); and group 2 consisted of patients who spontaneously aborted (aborted group). There was a significant difference in inhibin A concentrations between the control and aborted groups at 8, 10, and 12 weeks' gestation. Significant differences in beta-hCG concentrations between the two groups is evident only at 10 weeks' gestation. There were no significant differences in inhibin pro-alphac concentrations between the two groups at any gestational age. Assessment of the trend in the control group over the study period showed a significant increase in inhibin A and beta-hCG but not inhibin pro-alphac levels.

CONCLUSION(S)

Low serum levels of inhibin A at early gestational age in pregnancies destined to miscarry suggest a role for this glycoprotein as a marker for early pregnancy viability. Its measurement at the time of the first pregnancy test might be able to predict pregnancy outcome.

Inhibin A, inhibin B and activin A concentrations in umbilical cord artery and vein

Activin A and inhibins (A and B) are growth factors expressed during pregnancy by the human placenta, decidua and fetal membranes, and by several fetal organs. They are secreted in both the maternal and the fetal circulations, but the net contribution of the fetus to inhibins/activin A production is still unclear. In the present study we determined whether there was a difference in the serum concentration of activin A, inhibin A and inhibin B between the artery and vein of the umbilical cord. Arterial and venous umbilical cord blood was obtained immediately before elective Cesarean section of 16 term infants from uncomplicated pregnancies. Inhibins and activin A levels were assayed by specific enzyme-linked immunosorbent assays. The paired t-test and linear regression analysis were used to calculate statistical significance. Inhibin A levels did not differ between the artery and vein of the umbilical cord. In contrast, arterial inhibin B levels were significantly (p < 0.001) lower, and activin A concentrations significantly (p < 0.05) higher than the respective venous concentrations. A significant correlation between arterial and venous levels of inhibin A (r = 0.591; p < 0.05), inhibin B (r = 0.749; p < 0.0001) and activin A (r = 0.571; p < 0.05) was found. The present findings suggest that the human placenta is the main source of inhibin B, and the fetus of activin A, in the umbilical cord. In light of the possible roles played by inhibin and activin in erythroid differentiation, protection of neurons against brain injury and modulation of adrenal and pancreatic hormone release, the present data may be of help in evaluating their changes in the umbilical cord when gestational diseases occur.

Gonadotropins, prolactin, inhibin A, inhibin B, and activin A in human fetal serum from midpregnancy and term pregnancy

Using specific enzyme-linked immunosorbent assays we measured inhibin A, inhibin B, and activin A in relation to LH, FSH, and PRL in normal human fetal midpregnancy serum obtained by in utero cord venipuncture (n = 25) and compared these results to those in fetal serum from term pregnancies (n = 23). We also tested serum from fetuses with intrauterine growth retardation (n = 6) or trisomy 21 (n = 6). We found no measurable inhibin A, except in three midpregnancy males (3 of 14). Inhibin B, however, was detected in midpregnancy male fetuses (167+/-67 pg/mL) and was higher than that in females (16+/-12 pg/mL). It was present in male term fetuses (125+/-32 pg/mL), but not in females. The activin A levels did not significantly differ between term and midpregnancy males and females. LH and FSH were detected in midpregnancy male fetuses (4.4+/-3.3 and 0.77+/-0.49 mIU/mL, respectively), with higher levels in females (33.0+/-23.2 and 54.4+/-27.7 mIU/mL, respectively), and were suppressed at term. PRL did not exhibit sexual difference, but showed a higher level at term (322.4+/-113.8 ng/mL) than at midpregnancy (33.0+/-26.1 ng/mL). Comparison of inhibin B with FSH levels showed correlation coefficients of -0.565 at midpregnancy vs. +0.445 at term. Serum from fetuses with intrauterine growth retardation or trisomy 21 did not show any different hormonal profiles. These data suggest that inhibin B is probably an additional factor in FSH inhibition at midpregnancy, whereas activin A is not associated with any change in the different studied populations. We speculate that inhibin A could be a method to detect maternal blood contamination in cord venipuncture.

Activin A, inhibin A, inhibin B and parturition: changes of maternal and cord serum levels according to the mode of delivery

OBJECTIVE

To evaluate whether activin A, inhibin A, and inhibin B levels in maternal and umbilical artery serum change according to the mode of delivery.

DESIGN

Maternal and cord blood specimens were collected at term after spontaneous labour and vaginal delivery, or elective caesarean section.

SETTING

Universities of Pisa, Turin, Naples and Udine.

POPULATION

Forty-two healthy pregnant women, at 3940 weeks of gestation, divided into two subgroups: group 1 vaginal delivery (n = 21), were delivered of 10 female and 11 male infants; group 2 elective caesarean section (n = 21), were delivered of 11 female and 10 male infants.

MAIN OUTCOME MEASURES

Serum activin A, inhibin A, inhibin B concentrations in maternal and umbilical cord blood.

RESULTS

At vaginal delivery, maternal serum inhibin A and inhibin B levels were lower and activin A levels higher than at elective caesarean section. Maternal levels of activin A, inhibin A and inhibin B were constantly higher than in umbilical arterial blood, independent of the mode of delivery. No significant difference was observed in umbilical arterial serum levels of the three proteins between the two modes of delivery. Umbilical arterial serum activin A and inhibin A concentrations did not show a significant difference between male and female infants in either vaginal or caesarean section, but male infants showed inhibin B levels significantly higher than female, independent of the mode of delivery.

CONCLUSIONS

In the presence of active labour, the human placenta secretes larger amounts of activin A and lesser amounts of inhibin A and inhibin B into the maternal circulation. Inhibin-related proteins in the fetal circulation do not show differences according to the mode of delivery, suggesting that they have a different method of production or metabolic rate compared with maternal activin and inhibins.

Advance in the study of inhibin, activin and follistatin production in pregnant women

This review summarizes the new information on the studies of inhibin, activin, and follistatin production in the placenta during human pregnancy. Inhibin and activin exert suppressive and stimulatory effects, respectively, on the release of FSH in the pituitary. Follistatin is bound to inhibin and activin and indirectly modulates the FSH release. The placenta produces these three proteins. The serum levels of inhibin, activin, and follistatin are elevated in pregnant women and decrease after delivery. The trophoblast cells from term placenta secrete inhibin and activin in the primary cultures. The production and mRNA expression of inhibin and activin are regulated by several stimulatory and suppressive hormones and growth factors in placental tissues. cAMP, Ca2+, and protein kinase-C may be involved in intracellular signal transduction in trophoblasts. Activin receptors are present on placental cells. Follistatin inhibits the binding of activin to ActRII receptor. Abnormal levels of inhibin and activin in maternal serum are observed in problem pregnancies and gestational diseases. Inhibin, activin, and follistatin may play roles in the regulation of reproductive endocrinology in pregnant women and the embryo/fetal development.

Maternal serum inhibin-A and free beta-hCG concentrations in trisomy 21 pregnancies at 10 to 14 weeks of gestation

OBJECTIVE

To determine the relation between maternal serum inhibin-A and free beta-hCG concentrations in chromosomally normal pregnancies and to compare the two biochemical markers for their sensitivity in identifying trisomy 21 pregnancies.

SAMPLE

Inhibin-A and free beta-hCG were measured in maternal serum samples from 800 chromosomally normal singleton pregnancies at 10 to 14 weeks of gestation and 76 singleton pregnancies with fetal trisomy 21.

RESULTS

In the normal group maternal serum inhibin-A was significantly associated with both maternal weight and gestational age (F = 11.2, P < 0.0001). In pregnancies with trisomy 21 the maternal serum inhibin-A and free beta-hCG concentrations were significantly increased (mean difference inhibin = 0.51 SD, F = 18, P < 0.0001 and mean difference free beta-hCG = 1.13 SD, F = 80, P < 0.0001). For a 5% false positive rate, the sensitivity of maternal serum free beta-hCG in identifying pregnancies with trisomy 21 was 28.9% compared with 12.8% for maternal serum inhibin-A. Delta inhibin-A was significantly associated with delta-free beta-hCG (r = 0.345, P < 0.01) and the deviation from the normal mean for free beta-hCG was significantly greater than the deviation for inhibin-A (t = 4.0, P < 0.0001). For a 5% false positive rate, the sensitivity achieved by combining information from delta inhibin-A and delta free beta-hCG was similar to the sensitivity of free beta-hCG alone (30.3% compared with 28.9%).

CONCLUSION

At 10 to 14 weeks of gestation fetal trisomy 21 is associated with increased maternal serum inhibin-A and free beta-hCG levels. However, the degree of elevation of inhibin-A is less than that of free beta-hCG, and there is a significant association between levels of the two proteins. The sensitivity for trisomy 21 achieved with the combination of maternal serum inhibin-A and free beta-hCG is not significantly different from that achieved with maternal serum free beta-hCG alone.

Measurement of serum concentrations of inhibin-A (alpha-beta A dimer) during human pregnancy

OBJECTIVE

The aims were to measure concentrations of inhibin-A (alpha-beta A dimer) in peripheral serum during normal human pregnancy, to establish which molecular weight form(s) are present in pregnancy serum and to relate the concentrations of inhibin-A to those of oestradiol and progesterone.

DESIGN

In a retrospective cross-sectional study 211 serum samples collected at 2-week intervals from week 8 to 38 of gestation were analysed for inhibin-A by enzyme immunoassay and oestradiol and progesterone by radioimmunoassay. Pooled samples corresponding to first, second and third trimester were subsequently used for fast protein liquid chromatography chromatographic analysis of inhibin forms present.

PATIENTS

Blood samples were obtained from normal pregnant women attending the antenatal clinic.

RESULTS

Concentrations of inhibin-A in peripheral serum gradually decreased from 1.76 +/- 0.15 microgram/l in week 8 of gestation to 0.86 +/- 0.12 microgram/l in week 16 (P < 0.01). Concentrations remained low during the second trimester but increased markedly (P < 0.01) during the third trimester reaching a maximal value of 5.68 +/- 0.89 microgram/l in week 36. Chromatographic analysis of pooled serum samples from the first, second and third trimester showed that the fully processed 31-kDa molecule is the predominant circulating form of inhibin-A throughout human gestation. Likewise, only the 31-kDa form was identified in extracts of term placenta which contained approximately 20 micrograms inhibin-A/kg tissue.

CONCLUSION

Inhibin-A, principally the 31-kDa form, is present in peripheral blood throughout human gestation at concentrations up to 50 times greater than maximum values found during the spontaneous menstrual cycle (approximately 100 ng/l). The finding of highest serum values during the third trimester and of significant concentrations in term placenta firmly support a placental rather than luteal origin for this material.

Inhibin in normal and abnormal pregnancy: maternal serum concentration and partial characterization

OBJECTIVE

This study evaluated maternal serum inhibin concentration and molecular distribution in normal and abnormal pregnancies.

STUDY DESIGN

Serum inhibin levels were measured by radioimmunoassay in 33 abnormal pregnancies (23 singleton and 10 multiple gestations) and 33 matched controls and were compared with pregnancy variables.

RESULTS

In the controls serum inhibin concentrations rose with gestational age (correlation coefficient 0.358, p < 0.01) and were higher in mothers with female fetuses (p < 0.05). Inhibin levels were higher in the abnormal singleton pregnancies (2.69 +/- 1.41 ng/ml) than in controls (1.26 +/- 0.32 ng/ml, p < 0.0001) and increased more rapidly with gestational age in multiple pregnancies (p < 0.05). Gel filtration chromatographic analysis of immunoreactive inhibin revealed three peaks with the major form having an apparent molecular weight of 55 to 60 kd.

CONCLUSION

Maternal serum inhibin concentrations are affected by gestational age, fetal gender, and complications of pregnancy. Most of the immunoreactive inhibin in maternal circulation is a large-molecular-weight form.

Serum inhibin during lactation: relation to the gonadotrophins and gonadal steroids

OBJECTIVE

The aims of the study were to describe the changes in serum immunoreactive inhibin (INH) during normal lactation and to examine the relations between INH, oestradiol (E2) and follicle stimulating hormone (FSH), particularly during the first weeks post partum.

DESIGN

Blood samples were obtained from normally lactating women for hormone measurements at daily intervals until discharge from hospital, and subsequently at weekly intervals until the resumption of menses, or one year post partum.

SUBJECTS

Eighteen breast feeding women aged 27-36 years volunteered for the study.

MEASUREMENTS

INH, FSH, luteinizing hormone (LH), prolactin (PRL), E2, and progesterone (P4) were measured by standard radioimmunoassays. Non-linear modelling was used to quantify the hormone patterns observed.

RESULTS

Hormone levels were compared with those found in the follicular phase of the normal menstrual cycle. Levels of INH fell rapidly in the first week post partum and remained at the lower end of the follicular phase range for the period of study, rising only just prior to resumption of menses. E2 fell more slowly, into the follicular phase range, reaching the lower end of that range only at about approximately 100 days post partum. FSH levels were suppressed initially below the follicular phase range, commencing to rise 4.7-24 days post partum, reaching a plateau high in the follicular phase range 17.5-53 days post partum, and subsequently showing a slow decline. Human chorionic gonadotrophin (hCG), initially measured because of its cross-reactivity in the LH assay, fell rapidly post partum and LH remained in the low follicular phase range for several weeks. PRL fell slowly throughout and was still elevated at 150 days post partum, while P4 fell very rapidly and was less than 1 nmol/l until just prior to first menses.

CONCLUSIONS

Inhibin levels fall rapidly post partum and remain low until close to the time of resumption of follicular activity and menses. The post partum rise in serum FSH appears to be much more closely related to falling oestradiol levels than to the very early and rapid fall in inhibin. Oestradiol thus appears to be the predominant negative feedback factor influencing FSH secretion during the post partum period. The low inhibin levels may allow FSH to rise to levels high in the follicular phase range under the predominant negative feedback control of oestradiol. Inhibin levels do not appear to be a suitable marker of returning fertility.

Circulating inhibin levels in lactating and nonlactating women

OBJECTIVE

To investigate the role of inhibin in the human puerperium, by measuring serum levels of immunoreactive inhibin in both lactating and nonlactating women.

DESIGN

Prospective, comparative, open study.

SETTING

Department of obstetrics and gynecology of a university hospital.

PATIENTS

Fourteen healthy women who delivered at term: seven lactating women and seven nonlactating women treated with the dopamine-agonist CV 205-502.

MAIN OUTCOME MEASURES

Serum immunoreactive inhibin, PRL, FSH, LH, E2, and P.

RESULTS

All women showed a rapid decline of immunoreactive inhibin levels during the first postpartum days. Thereafter the pattern depended on the way of feeding. Nonlactating women, with their rapid return of pituitary and ovarian function, showed increasing immunoreactive inhibin levels to a maximum on day 24 (950 +/- 180 U/L). Lactating women did not show ovarian activity despite high FSH levels, and immunoreactive inhibin stayed on a low level (230 +/- 40 U/L on day 24). There was a significant correlation between immunoreactive inhibin and E2.

CONCLUSIONS

The rapid decline of immunoreactive inhibin (elimination of placental hormone) is followed by an increase in nonlactating women (production by the maturing follicle) and by persistently low levels in lactating women. The lack of adequate levels of immunoreactive inhibin in lactating women may be an explanation of the relatively high FSH levels during lactation.

Comparative regulation of inhibin, activin and human chorionic gonadotropin production by placental trophoblast cells in culture

In the present study, we investigated the roles of cyclic adenosine monophosphate (cAMP), intracellular calcium, glucocorticoids, protein kinase-C and gonadotrophin-releasing hormone (GnRH) in regulating human chorionic gonadotrophin (hCG), inhibin and activin production in cultured human term placental trophoblast cells. Inhibin and hCG were measured in conditioned media by radioimmunoassay, while putative forms of inhibin and activin were characterized by western blotting using affinity-purified antisera directed against the inhibin alpha- and beta A-subunits. Inhibin and hCG secretion were stimulated by dexamethasone (0.2 microM), GnRH (5-25 microM), calcium ionophore A23187 (0.2-1 microM), phorbol-12-myristate-13-acetate (22 nM) and epinephrine (1 microM), with increasing response over successive 24-h treatment periods. Two molecules Mr approximately 30 and 32 kDa appeared to be the predominant dimeric forms of inhibin secreted by the cells, while 26 kDa activin was present in excess over inhibin. Large amounts of 40-44 kDa protein were detected by the alpha-directed antisera only, which may be a form of the inhibin alpha-subunit precursor protein. Secretion of activin was responsive to phorbol ester-mediated stimulation but not to the presence of GnRH or elevated cAMP concentrations. The divergence in maternal serum inhibin and hCG concentrations during late pregnancy remains unexplained by these findings.

Inhibin as a marker for hydatidiform mole: a comparative study with the determinations of intact human chorionic gonadotrophin and its free beta-subunit

OBJECTIVE

The purpose of the study was to evaluate plasma inhibin as a marker of hydatidiform mole and to compare the results with intact human chorionic gonadotrophin (hCG) and its free beta-subunit.

DESIGN

Serial determinations of the plasma concentrations of inhibin, intact human chorionic gonadotrophin and its free beta-subunit in cases of hydatidiform mole over an average period of 140 days.

PATIENTS

Five cases of hydatidiform mole, including patients with spontaneous remission after evacuation or persistent trophoblastic disease.

MEASUREMENTS

Immunoreactive inhibin, hCG and free hCG beta-subunit were measured using standard enzyme immunoassays.

RESULTS

Inhibin and free hCG beta-subunit levels were greater than in normal pregnant women at the same gestational age. Only intact hCG could detect the persistence of trophoblastic tissue.

CONCLUSIONS

Our data suggest that inhibin, intact human chorionic gonadotrophin and free beta-subunit might be useful as diagnostic markers of molar pregnancies. However, the original method of intact hCG determination is still superior for follow-up.

Maternal serum inhibin levels in second-trimester Down's syndrome pregnancies

Maternal serum inhibin levels were measured in 19 second-trimester pregnancies affected by fetal Down's syndrome and 95 unaffected control pregnancies matched for gestational age. A statistically significant elevation was found in the affected pregnancies compared with the controls (Wilcoxon rank sum test: one-tail P = 0.02). The median level in the cases was 1.3 times that in the controls, with 95 per cent confidence limits of 0.9-1.9. Although the inhibin levels were unrelated to those of alpha-fetoprotein and unconjugated oestriol in the same samples, there was a statistically significant correlation with human chorionic gonadotropin. This together with the relatively small elevation in cases suggests that inhibin would be of limited value in maternal screening for Down's syndrome.

Serum immunoactive inhibin levels in early pregnancy after in vitro fertilization and embryo transfer

OBJECTIVE

To determine the maternal serum concentrations of inhibin, E2, P, and hCG in early pregnancies arising from IVF and ET or GIFT and to assess the value of these hormone measurements in determining outcome of pregnancy.

DESIGN

Serum immunoactive inhibin, E2, P, and hCG levels were measured in the first trimester of pregnancies after IVF-ET and GIFT procedures.

SETTING

In vitro fertilization and ET or GIFT was undertaken at Monash IVF, Melbourne, Victoria, Australia.

PATIENTS

At least two blood samples were collected from 117 women between 4 and 11 weeks of gestation.

MAIN OUTCOME MEASURES

The hormone concentrations in the IVF-ET and GIFT pregnancies were compared with those in pregnancies and related to outcome of pregnancy.

RESULTS

Serum inhibin levels in singleton pregnancies were significantly higher than in comparable normal pregnancies. In contrast to normal conceptions in which inhibin concentrations rose to peak at 11 weeks, the levels found in IVF-ET and GIFT singleton pregnancies were high at 5 weeks' gestation and declined subsequently. In twin pregnancies, the inhibin levels were significantly greater than those in singleton pregnancies. In biochemical pregnancies diagnosed by increasing hCG concentrations in the absence of an embryonic sac, inhibin levels were significantly lower than those found in singleton pregnancy, as were E2, P, and hCG levels. In anembryonic pregnancies, diagnosed by the confirmation of an intrauterine gestation sac with no evidence of a fetal complex, inhibin concentrations were highest at week 4 and declined, being significantly lower at all stages of gestation. In ectopic pregnancy, serum inhibin levels were lower at all stages of gestation, whereas E2 concentrations were not lower until 6 weeks and P levels until week 5. Serum hCG levels were significantly lower at all stages of gestation. In women with spontaneous abortions, inhibin levels were lower than singleton pregnancies at 7 weeks.

CONCLUSIONS

Serum inhibin concentrations are elevated in pregnancies arising from ovarian hyperstimulation in the first trimester when compared with those in normal pregnancy, probably as a result of the presence of multiple corpora lutea resulting from ovarian hyperstimulation. Serum inhibin, E2, P, and hCG are useful markers of abnormal pregnancy outcome.

The relationship between peripheral immunoactive inhibin, human chorionic gonadotrophin, oestradiol and progesterone during human pregnancy

OBJECTIVE

The objective of this study was to investigate serial changes in the plasma concentration of inhibin in both the very early days of pregnancy following implantation and in late pregnancy. The timing of the changes in inhibin concentration relative to changes in the concentrations of other hormones of pregnancy was also investigated.

DESIGN

Serial observations of the peripheral concentrations of inhibin and other hormones in two groups of healthy volunteers in (a) early pregnancy and (b) late pregnancy.

PATIENTS

(a) Four healthy women recruited on cessation of contraception prior to conception. (b) Nine healthy women recruited at the antenatal clinic.

MEASUREMENTS

In the early pregnancy subjects, the concentrations of inhibin, progesterone, oestradiol and hCG were measured in plasma samples obtained three times per week from day 8 to day 10 of each menstrual cycle until 11 weeks after the last menstrual period in the conception cycle. In the late pregnancy subjects, plasma samples were obtained at 4-week intervals from 12 weeks until term.

RESULTS

The concentration of inhibin, progesterone and oestradiol in conception cycles were similar to those in the preceding cycles until the mid/to late-luteal phase of the cycle when hCG was first measureable. By day 12 of the luteal phase the concentration of inhibin was significantly higher in the pregnancy cycle than in the non-pregnancy cycle (P < 0.05) and progressively increased after the time of the missed menstrual period. The concentration of inhibin reached a peak (513.0 U/l, CI 442.1-595.3) by day 47 when the concentration of hCG was maximal. In early pregnancy the concentration of inhibin was correlated with that of hCG (r = 0.361; P < 0.01) as well as progesterone (r = 0.584, P < 0.001) and oestradiol (r = 0.602, P < 0.001). After 12 weeks there was no significant correlation between hCG and inhibin although significant correlations persisted with progesterone (r = 0.553, P < 0.001) and oestradiol (r = 0.361, P < 0.01).

CONCLUSIONS

The corpus luteum makes a significant contribution to the production of inhibin in early pregnancy while after 12 weeks the placenta is the major source.

Second-trimester maternal serum immunoreactive inhibin as a marker for fetal Down's syndrome

We measured immunoreactive inhibin in the maternal serum of 80 pregnancies with a chromosomally normal fetus and ten Down's syndrome pregnancies in the second trimester. The inhibin level in all Down's syndrome pregnancies was above the normal median; the multiple of the normal median (MoM) was 1.9. We found a statistically significant difference between the levels of inhibin in unaffected and affected pregnancies (Kolmogorov-Smirnov test: p < 0.002). Using an arbitrarily chosen cut-off of 2.4 MoM, 40 per cent of Down's syndrome and 5 per cent of the normal pregnancies were found. We conclude that immunoreactive inhibin may be useful as a marker for fetal Down's syndrome.