Effects of assisted reproductive technologies on human sex ratio at birth.

OBJECTIVE: To investigate the effect of assisted reproductive technology (ART) treatments on the sex ratio of babies born. DESIGN: Assessment of direct effects of assisted conception through retrospective data analysis on the progeny sex ratio of treated women in the United Kingdom. SETTING: The study uses the anonymized register of the Human Fertilisation and Embryology Authority. PATIENT(S): A total of 106,066 babies of known gender born to 76,994 treated mothers and 85,511 treatment cycles between 2000 and 2010 in the United Kingdom. INTERVENTION(S): Intrauterine insemination, IVF, or intracytoplasmic sperm injection (ICSI). MAIN OUTCOME MEASURE(S): Sex ratio of babies born. RESULT(S): Intrauterine insemination, IVF, and ICSI lead to different sex ratios, highest after IVF (proportion male = mean 0.521 ± confidence interval 0.0056) and lowest under ICSI embryo transfer (0.493 ± 0.0031). In addition, for both ICSI and IVF, transferring embryos at a later stage (blastocyst) results in approximately 6% more males than after early cleavage-stage ET. CONCLUSION(S): Because the cumulative number of IVF babies born is increasing significantly in Britain and elsewhere, more research is needed into the causes of gender bias after ART and into the public health impact of such gender bias of offspring born observed on the rest of the population.