Bone resorption starts at 14 days of treatment with gonadotropin-releasing hormone agonist in in vitro fertilization cycles.

The effect of gonadotropin-releasing hormone agonist (GnRH-a) use on bone turnover was investigated in a prospective cohort study of female patients undergoing in vitro fertilization (IVF) treatment. In 46 couples diagnosed with male-factor infertility, the women underwent a long step-down ovulation induction protocol. Urinary cross-linked N-telopeptide (uNTx) level was used to demonstrate bone turnover rate and was measured at the first day of GnRH-a administration, the first day of gonadotropin administration, the day after human chorionic gonadotropin injection and 12 days after embryo transfer. Urinary NTx levels (mean ± standard deviation (SD)) were 71 ± 34, 81 ± 40, 81 ± 50 and 83 ± 47 nmol BCE/mmol creatinine (BCE, bone collagen equivalents), respectively. There was no statistically significant difference between the four measurements (p = 0.28). In 19 women GnRH-a was administered for &ges; 14 days. Urinary NTx values of this group and the remaining 27 patients after GnRH-a treatment were 96.2 ± 40.7 and 71.5 ± 36.8 nmol BCE/mmol creatinine (mean ± SD), respectively. The difference between these groups was statistically significant (p = 0.038). These findings suggest that < 14 days' use of GnRH agonist in IVF patients has no effect on bone metabolism. To our knowledge, this is the first study demonstrating that the effect of agonists on bone metabolism starts as soon as estradiol suppression has started. [ABSTRACT FROM AUTHOR]