The relationship between blastocyst morphology and the sex ratio of singleton births in single blastocyst transfer cycles: A retrospective cohort study

BackgroundTo study the relationship between blastocyst morphology and the sex ratio of singleton births in single blastocyst transfer cylces. MethodsThis retrospective cohort study included women who underwent in vitro fertilization/intracytoplasmic sperm injection-embryo transfer (IVF/ICSI-ET) from January 2017 to December 2019 and obtained a single live baby following a single blastocyst transfer. The sex ratio which influenced by many possible factors were studied. Age-stratified analysis was performed for the maternal and paternal groups younger and older than 35 years. The 3108 cycles included here were grouped by sex at birth (male: 1777 cycles and female: 1331 cycles). Blastocysts were conceived via 2834 IVF and 274 ICSI treatments, and were used for 1054 fresh ET cycles and 2054 frozen-thawed embryo transfer (FET) cycles. ResultsSex ratio among singleton of poor blastocyst decreased significantly compared to those of good blastocyst (51.5% vs 60%, P<0.001). The results of multivariate logistic analysis showed that high-quality blastocysts had a 151% higher probability of being male singleton than poor-quality blastocysts (P<0.001). Further stratified analysis shows that in both group younger than 35 the sex ratio increased significantly in grades A and/or B trophectoderm (P<0.001) and good-quality blastocysts (P<0.001). While grade A inner cell mass (ICM) degree was significantly associated with a lower sex ratio than grade B (P<0.05). ConclusionsA single high-quality blastocyst transfer was significantly associated with a higher neonatal sex ratio. Grade A trophectoderm and grade B ICM contributed to improving the implantation potential of male blastocysts, especially in infertile men or women [&le;]35 years old.