Do blastocysts like fresh air?

WFWW-Do blastocysts like fresh air?

Embryos are very sensitive to their environment. Issues such as temperature, light and atmosphere are critical to proper embryo development and thus to a center’s success rates.

A study in the June 2009 issue of the journal “Fertility and Sterility” supports our decision at Reproductive Partners some time ago to use low oxygen incubators. In this study blastocysts were cultured in atmospheres with either 6% carbon dioxide (CO2) in air, the equivalent to 19% O2, a two-gas system; or 5% O2, 6% CO2, and 90% nitrogen (N2), a three-gas system.

Three hundred ninety six women, were randomized to 197 cultures with the three-gas system and 199 cultures with the two-gas system. The outcome with the three-gas system compared with the two-gas system showed a statistically significantly increased blastocyst rate (47.8% vs. 42.1%), mean number of blastocysts (3.8 vs. 3.3), and number of cryopreserved blastocysts (1.7 vs. 1.1). The mean number of transferred blastocysts was 1.2 versus 1.3. Culture with the three-gas system increased the relative birth rate by 10% compared with the two-gas system (42% vs. 32%, respectively), a statistically significant difference. The overall twin rate was 4.8%.
They concluded that blastocyst culture with low-oxygen (5%) versus high-oxygen (19%) concentration yielded a better blastocyst outcome and a marked improvement in birth rate.

Sex Ratio/Identical Twins in Blastocyst Transfer

WFWW-Sex Ratio and Identical Twinning in Blastocyst Transfer


One of the most frequent questions I am asked is whether IVF treatment, and blastocyst transfer in particular, increase the number of offspring of one sex.

According to a compilation of four studies published in the June 2009 issue of Fertility & Sterility, a higher male-female ratio after Day 5 blastocyst transfer compared with Day 3 cleavage-stage ET was 1.29:1 in favor of male offspring. This is not high enough to recommend this as a sex selection technique, but will be somewhat reassuring to those wanting a male child.

The study also looked at the chance of identical twins (monoztgotic twinning-MZT) in Day 5 transfers which has been said to be increased over Day 3 transfers or natural conception. They reviewed the results of nine studies incorporating almost 41,000 cycles and found the risk of MZT after blastocyst transfer was significantly higher compared with cleavage-stage transfer by a factor of 3.04:1. MZT is not a desirable result as it can create a more risky pregnancy for the babies, especially if they are in the same amniotic sac.