OBJECTIVETo study the factors that affect the sex ratio of live births in procedures of assisted reproductive technology (ART).

METHODSThe clinical data were collected from 4348 IVF-ET/freeze-thawed embryo transfer cycles that led to the birth of 5606 babies of known gender between 2008 and 2014. We assessed the impact of maternal age, paternal age, insemination method, the type of embryo transferred, stage of embryo transferred, single and twin births, previous abortion following ART, and cause of infertility on the sex ratio of the live births.

RESULTSThe total cohort included 3019 male and 2588 female babies, with a general sex ratio of 116:100. The sex ratio was 117:100 among singleton deliveries and 116:100 among twin deliveries. The sex ratio was 117:100 among the first births with ART treatment and 117:100 among the second births. For singleton deliveries, an advanced maternal age or paternal age was significantly correlated with an elevated sex ratio of births (58.4% vs 52.8%, P=0.012; 56.4% vs 52.3%, P=0.026), while ICSI was significantly correlated with a decreased sex ratio of births (45.7% vs 55.6%, P<0.001); for twin deliveries, none of the these factors was significantly correlated with the sex ratio of birth. For the first baby born after ART treatment, an advanced maternal age was significantly related to an increased sex ratio of births (57.4% vs 53.0%, P=0.009), while ICSI was significantly related to a decreased sex ratio of births (48.6% vs 55.4%, P=0.001); for the second baby born with ART treatment, none of these factors was significantly correlated with the sex ratio of birth. Univariate logistic regression analysis showed that the maternal age (OR:0.836, 95% CI 0.731-0.955, P<0.05) and insemination method (OR:1.151, 95% CI 1.027-1.289, P<0.05) were significantly related to the sex ratio of birth, but in multivariable logistic regression analysis, after controlling for compounding factors, none of these factors was identified as independent predictive factors for sex ratio of births.

CONCLUSIONSAn advanced maternal age is related to a higher live birth sex ratio, while ICSI is related to a decreased percentage of male babies. For singleton deliveries, an advanced paternal age is related to a higher sex ratio of births.