Abstract: The search retrieved 1585 records; from those five studies were eligible, including 351 women (intervention = 166; control = 185). All studies were judged to be at high risk of bias. All reported per-woman rather than per-cycle data. When use of low-dose hCG to replace FSH was compared with conventional COH for the outcome of live birth, confidence intervals were very wide and findings were compatible with appreciable benefit, no effect or appreciable harm for the intervention (RR 1.56, 95% CI 0.75 to 3.25, 2 studies, 130 women, I² = 0%, very-low-quality evidence). This suggests that for women with a 14% chance of achieving live birth using conventional COH, the chance of achieving live birth using low-dose hCG would be between 10% and 45%. Similarly confidence intervals were very wide for the outcome of OHSS and findings were compatible with benefit, no effect or harm for the intervention (OR 0.30, 95% CI 0.06 to 1.59, 5 studies, 351 women, I² = 59%, very-low-quality evidence). This suggests that for women with a 3% risk of OHSS using conventional COH, the risk using low-dose hCG would be between 0% and 4%. The confidence intervals were wide for the outcome of ongoing pregnancy and findings were compatible with benefit or no effect for the intervention (RR 1.14, 95% CI 0.81 to 1.60, 3 studies, 252 women, I² = 0%, low-quality evidence). This suggests that for women with a 32% chance of achieving ongoing pregnancy using conventional COH, the chance using low-dose hCG would be between 27% and 53%. The confidence intervals were wide for the outcome of clinical pregnancy and findings were compatible with benefit or no effect for the intervention (RR 1.19, 95% CI 0.92 to 1.55, 5 studies, 351 women, I² = 0%, low-quality evidence). This suggests that for women with a 35% chance of achieving clinical pregnancy using conventional COH, the chance using low-dose hCG would be between 32% and 54%. The confidence intervals were very wide for the outcome of miscarriage and findings were compatible with benefit, no effect or harm for the intervention (RR 1.08, 95% CI 0.50 to 2.31, 3 studies, 127 pregnant women, I² = 0%, very-low-quality evidence). This suggests that for pregnant women with a 16% risk of miscarriage using conventional COH, the risk using low-dose hCG would be between 8% and 36%. The findings for the outcome of FSH consumption were compatible with benefit for the intervention (MD -639 IU, 95% CI -893 to -385, 5 studies, 333 women, I² = 88%, moderate-quality evidence). The findings for the outcome of number of oocytes retrieved were compatible with no effect for the intervention (MD -0.12 oocytes, 95% CI -1.0 to 0.8 oocytes, 5 studies, 351 women, I² = 0%, moderate-quality evidence). We are very uncertain of the effect on live birth, OHSS and miscarriage of using low-dose hCG to replace FSH during the late follicular phase of COH in women undergoing ART, compared to the use of conventional COH. The current evidence suggests that this intervention does not reduce the chance of ongoing and clinical pregnancy; and that it is likely to result in an equivalent number of oocytes retrieved expending less FSH. More studies are needed to strengthen the evidence regarding the effect of this intervention on important reproductive outcomes.

Plain-language summary: Follicle-stimulating hormone (FSH) - a relatively expensive drug - is commonly used for several days to stimulate the ovaries of women undergoing assisted reproduction. Initial studies have shown that after a few days of using FSH to stimulate the ovaries, it can be replaced by human chorionic gonadotropin (hCG), which is less expensive. In addition to cost reduction, this intervention has a theoretical potential to reduce the risk of ovarian hyperstimulation syndrome (OHSS); though the underlying risk is already very low for most women. We searched the medical literature on in February 2013 for studies that evaluated the effectiveness and safety of using low-dose hCG to replace FSH during the late follicular phase in women undergoing controlled ovarian hyperstimulation (COH) for assisted reproduction, compared to the use of a conventional COH protocol. Five studies evaluating 351 women were included in this review. These studies were funded by fertility centres, universities, or both. We are very uncertain of the effect of this intervention on live birth, OHSS and miscarriage When use of low-dose hCG to replace FSH was compared with conventional COH, there was very low quality evidence compatible with appreciable benefit, no effect or appreciable harm for the intervention, suggesting that for women with a 14% chance of achieving live birth using a conventional COH, the chance of achieving live birth using low-dose hCG would be between 10% and 45%. Similarly, there was very low quality evidence suggesting that for women with a 3% risk of OHSS using a conventional COH, the risk using low-dose hCG was also compatible with either benefit or harm, and would be between 0% and 4%. Additionally we observed that there was low quality evidence suggesting that for women with a 32% chance of achieving ongoing pregnancy using a conventional COH, the chance using low-dose hCG was compatible with either benefit or no effect, and would be between 27% and 53%. There was low quality evidence suggesting that for women with a 35% chance of achieving clinical pregnancy using a conventional COH, the chance using low-dose hCG was compatible with either benefit or no effect, and would be between 32% and 54%. There was very low quality evidence suggesting that for pregnant women with a 16% risk of miscarriage using a conventional COH, the risk using low-dose hCG was compatible with either benefit or harm, and would be between 8% and 36%. We also observed that there is moderate-quality evidence that this intervention reduces the total FSH consumption and is unlikely to materially affect the number of oocytes retrieved Our conclusions are that we are very uncertain of the effect on live birth, OHSS and miscarriage of using low-dose hCG to replace FSH during the late follicular phase of COH in women undergoing ART, compared to the use of conventional COH. The current evidence suggests that this intervention does not reduce the chance of ongoing and clinical pregnancy; and that it is likely to result in an equivalent number of oocytes retrieved expending less FSH. More studies are needed to strengthen the evidence regarding the effect of this intervention on important reproductive outcomes.