Low-oxygen compared with high-oxygen atmosphere in blastocyst culture, a prospective randomized study

To investigate birth rates with two oxygen (O(2)) concentrations in blastocyst culture.

Randomized trial.

Private in vitro fertilization (IVF) clinic.

Six hundred women undergoing IVF.

Blastocyst culture in atmospheres with either 6% carbon dioxide (CO(2)) in air, the equivalent to 19% O(2), a two-gas system; or 5% O(2), 6% CO(2), and 90% nitrogen (N(2)), a three-gas system.

Birth rate.

The inclusion criterion for blastocyst culture (at least five fertilized oocytes) was fulfilled in 396 women, 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%.

Blastocyst culture with low-oxygen (5%) versus high-oxygen (19%) concentration yielded a better blastocyst outcome and a marked improvement in birth rate. Generation of cytotoxic reactive oxygen species with prolonged embryo culture might deteriorate blastocyst viability.