Factors related to early spontaneous miscarriage during IVF/ICSI treatment: an analysis of 21,485 clinical pregnancies

Research question: Which factors are related to early spontaneous miscarriage in IVF-conceived clinical pregnancies? Design: A total of 21,485 clinical pregnancies were included in the analysis. First, early spontaneous miscarriage rates were compared among different groups according to female age, body mass index (BMI), number of previous miscarriages, infertility diagnosis and type and cycle characteristics. Then, the spontaneous miscarriage rate in patients with polycystic ovary syndrome (PCOS), uterus malformation and endometriosis was compared with that in patients with male factor infertility alone. Last, logistic regression was used to analyse factors affecting the early spontaneous miscarriage rate. Results: Of the 21,485 cycles, 2703 cycles (12.58%) resulted in early spontaneous miscarriage. In patients <35 years old, those with uterus malformation or PCOS experienced significantly higher spontaneous miscarriage rates (14.44% versus 9.47%, P = 0.027; 11.43% versus 9.47%; P = 0.003) compared with controls (male factor only). In multivariate logistic regression analysis, the spontaneous miscarriage rate increased in frozen embryo transfer cycles in patients <35 years old (odds ratio [OR] 1.449, 95% confidence interval [CI]1.303-1.611, P = 0.000), but decreased in patients >= 35 years old (OR 0.794, 95% CI 0.671-0.939, P = 0.007) compared with fresh cycles. Conclusions: Female age, number of previous miscarriages and endometrial thickness on the day of embryo transfer were independent factors associated with early spontaneous miscarriage. PCOS, uterus malformation and frozen embryo transfer significantly increased spontaneous miscarriage rate in patients <35 years old compared with male factor alone controls. However, frozen embryo transfer decreased the spontaneous miscarriage rate in patients >= 35 years old compared with fresh cycles.