The risk of monozygotic twins in assisted conception is 2.25 times higher than the natural conceptions. Larger studies reporting on monozygotic twinning following single-embryo transfer or after post-natal confirmation of zygosity with DNA analysis are warranted before definitive conclusions can be drawn and guidelines produced. In order to provide adequate pre-conceptional counselling, it is important to monitor the incidence of monozygotic twins in both natural and assisted conceptions. We suggest building a national multiple pregnancy database based on accurate diagnosis of zygosity.

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S. Roberts is supported by the NIHR Manchester Biomedical Research Centre.

The aims of this prospective study were to investigate the relationship between anti-Müllerian hormone (AMH) and antral follicle count (AFC), and to determine whether these markers of ovarian reserve correlate with lifestyle factors, ethnicity, chronological age and reproductive history. Participants were 136 normo-ovulatory women undergoing infertility work-up within 3 months of their first ovarian stimulation cycle for in vitro fertilization. On day 3 of a spontaneous menstrual cycle, a blood sample for measurement of plasma AMH levels was taken and a transvaginal ultrasound scan to determine the AFC (follicles measuring 2-5 mm in diameter) was performed. Information about smoking, body mass index, alcohol consumption, ethnic origin, chronological age, age at menarche, years since menarche and gravidity were recorded using a case report form. The main outcome measures were plasma AMH concentrations and total number of small antral follicles (AFC). Median plasma levels of AMH were 2.0 ng/ml (interquartile range 1.1-3.6) and AFC was 10 (interquartile range 7-15). A positive correlation between AMH and AFC (r = 0.54, p < 0.0001) was found. AMH and AFC correlated negatively with age (r = -0.30, p < 0.001 and r = -0.27, p = 0.001 respectively) and number of years since menarche (r = -0.23, p = 0.007 and r = -0.21, p = 0.015 respectively), but not with any of the other measures. Circulating AMH levels and AFC correlated with each other and declined significantly with age. There were only weak, non-significant, correlations with lifestyle factors and reproductive history. These putative markers could be used individually or together to assess the age-related decline of ovarian function in normo-ovulatory candidates for IVF.

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AMH may exhibit assay-specific preanalytical instability. Robust protocols for the development and validation of commercial AMH assays are required.