Maternal serum inhibin levels in twin and singleton pregnancies conceived by assisted reproduction

BACKGROUND: To investigate whether second trimester serum inhibin levels differ in pregnancies conceived by assisted reproduction technology (ART). METHODS: In Israel, serum samples from twin pregnancies were obtained for inhibin testing from women either referred for routine ultrasound monitoring, follow up after multi-fetal reduction or amniocentesis, largely for advanced maternal age. In the UK, inhibin had been tested prospectively in singleton and twin pregnancies of women having routine Down's syndrome (DS) screening. Results were available from 207 ART pregnancies: 170 singletons and 37 twins. This includes 15 twins from Israel, known to have been reduced from triplets to twins. Comparison was made with 4384 spontaneous pregnancies: 4334 singletons and 50 twins. Results were expressed in multiples of the gestation-specific median (MoM) for normal spontaneous pregnancies. RESULTS: In ART singletons, the median maternal inhibin level was higher (1.11 MoM) than in spontaneous singletons (0.99 MoM, P < 0.001, two-tail Wilcoxon Rank Sum Test). In twins, there was no material difference between ART and spontaneous pregnancies with medians of 1.98 and 2.18 MoM, respectively (P = 0.62). There was no effect of multi-fetal reduction, with medians of 1.76 and 1.81 MoM in reduced and non-reduced twins, respectively (P = 0.46). CONCLUSION: It appears that serum inhibin levels are increased on average in ART singletons but not in ART twin pregnancies. More data will be needed before deciding whether risk calculation parameters need to be altered when using inhibin for DS screening in pregnancy.