(rhCG) in assisted of a clinical trial comparing two for induction of final maturation in in vitro Steril

570 (single 500 μg dose of rHCG) may lead to a higher rate of OHSS compared with a 250 μg dose, with no significant improvement in pregnancy rate. As both safety and efficacy are required for any medication, the dose of 250 μg seems the dose of choice for triggering ovulation.’ While we agree that a dose of 250 μg is sufficient to achieve ovulation trigger for the majority, we have some reservations in condemning the use of 500 μg rHCG completely. We have recently published a randomized controlled trial which further confirmed the equivalence of 250 μg and 500 μg rHCG on inducing final oocyte maturity (Chan et al., 2005). In our study, the incidence of mild to moderate OHSS was less in the 500 μg rHCG group (7%), when compared to the 13% in the 250 μg rHCG group, although the difference was not statistically significant. We have deliberately excluded patients who were at risk of OHSS from recruitment into the study, which may explain the seemingly paradoxical observation and that no severe OHSS was recorded. The data from either study did not support the notion that a higher dose of rHCG is associated with a higher incidence of OHSS. There is little controversy in the effectiveness of the two difference doses of rHCG in ovulation trigger, either defined by the mean number of oocytes retrieved per patient (Chang et al., 2001) or the percentage of metaphase II oocytes per patient (Chan et al., 2005). Nevertheless, there are some subtle differences between the two groups of patients. For example, the numbers of two-pronuclear fertilized oocytes and cleaved embryos were significantly higher in the 500 μg rHCG group (Chang et al., 2001). In our study, the serum and follicular fluid HCG levels on day HCG +2 as well as the follicular fluid:serum HCG ratio were significantly higher in the 500 μg rHCG group, indicating a better delivery of HCG from the serum to the follicle (Chan et al., 2005). The serum estradiol and progesterone levels were significantly higher in the 500 μg rHCG group in the luteal phase in both studies. Whether such differences in the embryo variables and hormone profiles confer a better environment for successful implantation is unknown. Although the implantation rate did not differ in both studies, neither of them was powered to detect this difference. The problem of high body mass index (BMI) and the poor response in obese patients to a standard amount of HCG are well recognized. Indeed, we have shown that the absorption of HCG in the obese women was only half of that of women with normal BMI (Chan et al., 2003). Both studies comparing the two different doses of rHCG excluded obese women (Chang et al., 2001; Chan et al., 2005). For those with a higher BMI, a higher dose of rHCG may be required to achieve the same ovulation trigger. We therefore recommend that the higher dose should be considered in selected patients who have a high BMI and a low risk of OHSS.