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

OBJECTIVE

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

DESIGN

Randomized trial.

SETTING

Private in vitro fertilization (IVF) clinic.

PATIENT(S): Six hundred women undergoing IVF.

INTERVENTION(S): 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.

MAIN OUTCOME MEASURE(S): Birth rate.

RESULT(S): 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%.

CONCLUSION(S): 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.