Influence of oocytes and spermatozoa on early embryonic development.

Objective: To evaluate the effect of oocytes and spermatozoa on early embryonic development.

Design: Retrospective study.

Setting: Infertility Clinic, the Family Federation of Finland.

Patient(s): Fifty-nine oocyte donation cycles with oocytes shared among 118 recipient couples.

Intervention(s): Culture of all fertilized oocytes.

Main Outcome Measure(s): Standard sperm (concentration, progressive motility, and morphology according to Tygerberg strict criteria) and embryo (morphology and cleavage stage) characteristics.

Result(s): A marked effect of the oocyte on both embryo morphology and blastomere cleavage rate was demonstrated. In addition, a significant sperm effect on blastomere cleavage rate was found. Sperm morphology as determined according to strict criteria rather than sperm count or progressive motility was positively associated with the blastomere cleavage rate. None of the measured sperm characteristics influenced embryo morphology.

Conclusion(s): Embryo morphology, i.e., fragmentation and blastomere uniformity, are predominantly determined by oocyte quality, whereas both the oocyte and spermatozoa influence the blastomere cleavage rate.