Sex ratio after day 2, day 3 or blastocyst transfer.

Facultative adjustment of mammalian sex ratios in support of the Trivers–Willard hypothesis: evidence for a mechanism

“…A similar pattern emerges with human blastocysts used for in vitro fertilization; more differentiated cells result in a male-biased sex ratio (e.g. Mercader et al 2001;Milki et al 2003). The glucose added to in vitro cultures enhances male conceptus growth and development, but inhibits female conceptus growth and development, causing the difference in sex ratios between conceptuses raised in vivo and in vitro (Larson et al 2001).…”

Impact of blastocyst transfer on offspring sex ratio and the monozygotic twinning rate: a systematic review and meta-analysis

“…When we analyzed the M/F ratio after adding data from four unpublished studies (20)(21)(22)(23), blastocyst transfer resulted in an M/F ratio of 1.36 (1,071/ 790), which was significantly different from 1.05 (1,279/1,220) for the early cleavage-stage ET. The OR using fixed effect model was 1.29 (95% CI 1.13-1.47; I 2 ¼ 0%), which is almost equal to the OR including four published studies.…”

“…Five abstracts were excluded because of the absence of peer-review process and a full-length original article (15,(20)(21)(22)(23). Two reports on sex ratio imbalance after blastocyst transfer were excluded because there were no comparative data for blastocyst versus cleavage-stage ETs (5,24).…”

Blastocyst embryo transfer is associated with a sex-ratio imbalance in favor of male offspring

“…The only two studies (an abstract and a peer-reviewed report) that encountered a significant shift toward male offspring after ETs involved the coculture of blastocysts, a technique no longer permitted in the United States (14,15). Kausche et al described a small shift in the sex ratio toward males (16), perhaps because these authors performed transfers on day 6 of embryo culture, allowing for the slowerdeveloping blastocysts to expand more fully and reach a similar developmental grade to the faster-developing blastocysts on day 5.…”