The effects of fertilization mode, embryo morphology at day 3, and female age on blastocyst formation and the clinical outcomes

Abstract

The aim of this study was to evaluate the influence of in vitro fertilization (IVF) versus intracytoplasmic sperm injection (ICSI), fertilization mode embryonic morphology at day 3, and female age on blastocyst development, on the clinical outcomes of pregnancy after blastocyst transfer. A total of 471 cycles were retrospectively investigated. The rates of blastocyst formation and of good blastocyst morphology were higher in IVF than in ICSI cycles but there were no significant differences in the clinical pregnancies or in the miscarriage rates. The rates of formation of blastocyst and of blastocysts with good morphology were significantly higher from good-morphology embryos than from poor-morphology embryos. Nevertheless, 16.9% of the poor-morphology embryos reached the blastocyst stage. The total rates of blastocyst formation, and rates of clinical pregnancy and implantation were statistically similar in the age <35, 35–39, and >39 year groups, although tending to decrease with increasing age. When equal numbers of embryos were transferred on day 3, the rates of clinical pregnancy and implantation after blastocyst transfer were significantly higher in the <35 year age group than in the 35–39 and >39 year age groups, which were not significantly different. The miscarriage rates after embryo or blastocyst transfers were not statistically different in groups of similar age. Therefore, extended embryo culture up to the blastocyst stage could be implemented for women aged younger than 35 years to increase the pregnancy rate. For older women, transfer and vitrification of available embryos at day 3 and extended culture of morphologically poor embryos to the blastocyst stage for cryopreservation may improve the clinical outcome.

• Age
• blastocyst
• implantation rate
• long-term culture
• pregnancy rate

Declaration of interest

None of the authors have any conflicts of interest.

Author contributions

Conception and design of the experiments: HY, HJ; Performance of the experiments: HY, HJ, RH, CW, JZ, KL; Analysis of the data: HY; Contribution of reagents, materials, and analysis tools: RH; Writing of the manuscript: HY, HJ.