Bovine Blastocyst Development In Vitro: Timing, Sex, and Viability Following Vitrification1

Abstract

Selection of blastocysts based on their morphological characteristics and rate of development in vitro can skew the sex ratios. The aim of this study was to determine whether an embryo's developmental rate affects its survival after vitrification, and whether male and female embryos survive vitrification differently. In vitro fertilized bovine oocytes were cultured in potassium simplex optimized medium (KSOM) + 0.1% BSA for 96 h, and then into KSOM + 1% BSA (KSOM) or in sequential KSOM + 0.1% BSA for 96 h, and then into synthetic oviduct fluid (SOF) + 5% FBS (KSOM-SOF). In part 1 of this study, embryos cultured in each medium that had developed into blastocysts at approximately 144, 156, or 180 h were recovered from culture, graded, and then vitrified. After warming, blastocyst survival rates were immediately evaluated by reexpansion of the blastocoels. In the second part of the study, all blastocysts (n = 191) were sexed by polymerase chain reaction 48 h after warming. When cultured in KSOM medium, more 144-h blastocysts survived vitrification (68%) than blastocysts vitrified at 180 h (49%). Blastocysts derived at 156 h in KSOM-SOF survived vitrification better (87%) than blastocysts vitrified at either 144 h or 180 h, and subsequently hatched at a greater rate than those vitrified at 180 h. The overall blastocyst survival rates did not differ significantly whether embryos were cultured in KSOM or sequential KSOM-SOF. Blastocysts derived at 144 and 156 h in KSOM or KSOM-SOF were predominately male, and significantly more of them survived vitrification 48 h after warming. However, blastocysts cultured in KSOM-SOF, and then vitrified at 180 h were predominately female. Overall, blastocysts that survived vitrification, and subsequently hatched 48 h after warming, were male. In summary, embryos that reached the blastocyst stage earlier were predominantly males; these males had better morphology, endured vitrification, and subsequently hatched at a greater rate than did female blastocysts.

Chromosome distribution of early miscarriages with present or absent embryos: female predominance

“…Faster male embryos development than female ones were discovered in some animal studies [18,19]. A cytogenetic examination of 342 spontaneous abortions divided into three groups according to the severity of embryonic developmental disturbance, and in which the likelihood of maternal cell contamination was low following analysis of embryonic and parental DNA, suggested, based on the maleto-female ratios, that the expression of genes from the maternal X-chromosome in XY embryos may enhance more stable development during early embryogenesis [7] because that one of the two copies of X chromosome on female was inactivated randomly during embryogenesis (X-chromosome inactivation).…”

Blastocyst transfer and gender: IVF versus ICSI

“…In animals, it has been demonstrated that the fastest growing embryos are more commonly male [22]. Several hypotheses have been addressed trying to explain this finding.…”

Conception rate after sex determination and cryopreservation of D7 bovine embryos:

“…King et al (1992) and Gutierrez-Adan et al (2001) found that male embryos were more resistant to manipulation and cultivation. Nedambale et al (2004) recovered IVP embryos from culture and then after vitrification. After warming, the embryos were cultured for 48 h and sexed by PCR.…”