Relaxin in sera during the luteal phase of in-vitro fertilization cycles

Summary. To identify the time when relaxin can first be detected in peripheral sera after in-vitro fertilization (IVF) and embryo transfer, blood samples were collected from 20 women up to 14 days after oocyte retrieval. Sixteen women did not become pregnant and in eight of them relaxin (but not beta-human chorionic gonadotrophin, (β-hCG) was measurable for the first time at days 6 to 12. Concentrations of other hormones measured were also different in these eight women compared with the remaining eight non-pregnant women; their serum concentrations of 17α-OH progesterone, progesterone and oestradiol were higher but concentrations of luteinizing hormone and follicle-stimulating hormone were lower. Three women became pregnant; relaxin and β-hCG were first detected on the same day (10 to 12). The remaining woman had increased β-hCG levels but did not develop a clinical pregnancy. Measurement of serum relaxin during IVF cycles may allow assessment of corpora luteal function before its identification by levels of steroid hormones.