The effect of different temperature conditions on human embryosin vitro

RESEARCH QUESTION: What temperature is optimal for human embryo development up to day 5 or 6?

DESIGN: Two prospective sibling oocyte studies on culture temperature were conducted in a university-based tertiary referral centre. Eligibility critera for both studies: Study 1: 50 cycles between August and October 2015, with culture at a stable temperature (37.0°C ± 0.3°C) or culture using a circadian temperature rhythm (CTR) (1 am to 6 am: 36.6°C, gradual increase to 37.5°C; 11 am to 9 pm: 37.5°C; gradual decrease to 36.6°C); study 2: 99 cycles between April and November 2016, with stable culture at 36.6°C or 37.1°C.

PRIMARY OUTCOME MEASURES: fertilization and embryo development (top and good quality) up to day 5 or 6, and utilization rate (number of embryos transferred and cryopreserved per zygote). Secondary outcome measure: clinical pregnancy (number of pregnancies with at least one gestational sac).

RESULTS: An incubator with CTR was used for culture. An effect was found on embryo development (utilization rate: 42.1% versus 32.6%; P = 0.014), but not on clinical pregnancy rate (60.0% versus 45.5%; P = 0.670). Stable culture at 36.6°C or 37.1°C did not affect embryo development (utilization rate: 40.0% versus 40.4%; P = 0.905); clinical pregnancy rate was improved by culture at 37.1°C (46.4% versus 74.2%; P = 0.036).

CONCLUSION: Culture in an incubator with CTR does not improve fertilization rate or embryo quality. Embryo culture at 36.6°C or 37.1°C showed similar embryo development.