LETTER TO THE EDITOR Coasting resulting in a sharp decline in serum estradiol does not compromise implantation To the Editor: We read the retrospective analysis of Abdalla and Nicopoullos (1) with great interest. We agree with the results, especially regarding the effects of estradiol drop (E2d). As was previously mentioned in the early studies, no strict, evidence-based criteria were established regarding the initial estradiol level (E2i) to start coasting that would not compromise oocyte/embryo quality or implantation capacity of the embryos. Moreover, there is not a safety threshold of E2d that determines whether to cancel or continue the IVF cycle (2–5). A short period of coasting (<3 days) is generally indicated as a major predictor of success among high responders (2). Today, it is acknowledged that >50% E2d does not seem to interfere with endometrial receptivity and/or implantation (2). Recently, in a report of two cases, we demonstrated that even more dramatic E2d (>76%) during coasting did not compromise implantation in GnRH agonist (GnRHa) cycles (6). Abdalla and Nicopoullos (1) clearly noted that neither E2i nor E2d has a negative effect on implantation, miscarriage, or live birth rates, except extremely low (<1,000 pmol/L) or high (>20,000 pmol/L) serum E2 levels at hCG triggering (E2hCG) (1). Unfortunately, the investigators did not separately analyze the data according to the protocol used: GnRHa or GnRH antagonist (GnRHant). It remains unclear whether a sharper decrease in serum E2 occurs in GnRHant cycles because of a potential direct effect of GnRHant. Literature is also lacking concerning the definitive impact of coasting in the GnRHant cycle, which is usually associated with a lower incidence of ovarian hyperstimulation syndrom (OHSS) compared with GnRHa cycles. In a small study, Bahceci et al. (3) reported favorable outcomes in high-responder patients undergoing controlled ovarian stimulation with GnRHant; however, in that study E2d was not severe, with a mean E2hCG level of 4,320  1,953 pg/ mL. Conversely, Farhi et al. (4) showed that targeted serum E2 concentrations were obtained within short coasting periods (<2 days) in antagonist cycles, which is associated with a higher E2d. Furthermore, in GnRHant cycles, despite similar OHSS incidence and preg- nancy rates, they observed a significant decrease in the number of oocytes harvested even in short coasting periods compared with GnRHa cycles. Aboulghar et al. (5) reported that in GnRHa cycles, cotreatment with GnRHant was superior to coasting with respect to duration of coasting and the number of oocytes retrieved and highquality embryos produced. Abdalla and Nicopoullos (1) defined that extremely low and high serum E2 levels (<1,000 pmol/L and >20,000 pmol/L) on the hCG day were found to be related to decreased implantation and pregnancy rates, despite unaffected retrieved oocyte number (1). However, they also found extremely low serum E2 levels on hCG day reduced fertilization rates (1). Therefore, the effects of serum E2 drop rate and serum E2 levels on hCG day remain controversial. Surprisingly, we achieved an unexpected triplet pregnancy despite >10 times E2d (9,299 declined to 798 pg/mL) subsequent to 4-day coasting, wherein three grade A embryos transferred (unpublished data). In conclusion, we believe that a favorable clinical outcome can be expected despite dramatic E2d obtained during coasting periods, even in GnRHant cycles. However, it remains unclear whether there is a serum E2 safety threshold during coasting, below which a pregnancy is unexpected in GnRHa or GnRHant cycles. Cem Somer Atabeko glu, M.D.a,b € Batuhan Ozmen, M.D.a,b Suheyla Isbacar, Ph.D.b Rusen Aytac, M.D.a,b Murat S€ onmezer, M.D.a,b a Ankara University School of Medicine, Department of Obstetrics and Gynecology, Ankara, Turkey b Ankara University Center for Research on Human Reproduction, Ankara, Turkey January 25, 2010 C.S.A. has nothing to disclose. B.O. has nothing to disclose. S.I. has nothing to disclose. R.A. has nothing to disclose. M.S. has nothing to disclose. doi:10.1016/j.fertnstert.2010.01.061 REFERENCES 1. Abdalla H, Nicopoullos JD. The effect of duration of coasting and estradiol drop on the outcome of assisted reproduction: 13 years of experience in 1,068 coasted cycles to prevent ovarian hyperstimulation. Fertil Steril 2009 [Epub ahead of print]. 2. Ulug U, Ben-Shlomo I, Bahceci M. Predictors of success during the coasting period in high-responder patients undergoing controlled ovarian stimulation for assisted conception. Fertil Steril 2004;82:338–42. 0015-0282/$36.00 3. Bahceci M, Ulug U, Tosun S, Erden HF, Bayazit N. Impact of coasting in patients undergoing controlled ovarian stimulation with the gonadotropin-releasing hormone antagonist cetrorelix. Fertil Steril 2006;85:1523–5. 4. Farhi J, Ben-Haroush A, Lande Y, Sapir O, Pinkas H, Fisch B. In vitro fertilization cycle outcome after coasting in gonadotropin-releasing hormone (GnRH) agonist versus GnRH antagonist protocols. Fertil Steril 2009;91:377–82. 5. Aboulghar MA, Mansour RT, Amin YM, AlInany HG, Aboulghar MM, Serour GI. A prospective randomized study comparing coasting with GnRH antagonist administration in patients at risk for severe OHSS. RBM Online 2007;5:271–9. 6. Atabekoglu C, Sonmezer M, Ozkavukcu S, Isbacar S. Unexpected pregnancy despite extremely decreased oestradiol levels during ovarian stimulation. Fertil Steril 2003;2008:90.e5–9. Fertility and Sterilityâ Vol. 94, No. 1, June 2010 Copyright ª2010 American Society for Reproductive Medicine, Published by Elsevier Inc. e29