P-135 No difference in morphokinetic patterns between male and female preimplantation embryos
Authors: Fraire-Zamora J , Martinez M , Torra-Massana M , Zamora M J , Vassena R , Miguel-Escalada I , Rodríguez A , Popovic M 
Published: June 2023

Abstract

Study question
Do morphokinetic parameters vary between male and female preimplantation embryos?

Summary answer
We observed no significant differences in morphokinetic characteristics between male and female preimplantation embryos

What is known already
Studies across various mammalian species, including humans, suggest that male and female embryos differ in their gene expression and metabolic phenotypes. These variations may inherently affect the timing and duration of key preimplantation events. In the context of ART, such developmental differences may ultimately bias embryo selection, leading to an unbalanced sex ratio in the resulting offspring. To date, only a few studies have explored the relationship between morphokinetic patterns and human embryo sex. While some suggest subtle sex-specific variations in human embryo growth dynamics, results have been conflicting and currently no clear consensus has been reached.

Study design, size, duration
Retrospective study of morphokinetic data obtained from 175 preimplantation embryos. The study included 175 cycles performed at two IVF centers, between March 2018 and June 2021. Only fresh oocyte donation cycles using intracytoplasmic sperm injection (ICSI) and fresh single embryo transfer (SET) were assessed. Sex of the embryos was obtained from live birth data. Overall, our analysis included 92 female and 83 male embryos.

Participants/materials, setting, methods
All embryos were cultured in a timelapse incubator in standardized conditions. The morphokinetic parameters assessed included: time to pronuclear fading (tPNf), times to 2–5 cells (t2, t3, t4, t5), time to 8 cells (t8), time to start of blastulation (tSB) and time to full blastocyst stage (tB). All parameters were measured in hours post insemination (hpi). A two-tailed Student’s t-test was used to compare morphokinetics between embryo sexes. A p&lt;0.05 was considered statistically significant.

Main results and the role of chance
We observed no significant differences in morphokinetic parameters when comparing cycles resulting in female vs. male live births: tPNf (21.8 ± 3.3 vs. 22.3 ± 3.4 hpi; p &gt; 0.39); t2 (24.6 ± 2.5 vs. 25.0 ± 2.5 hpi; p &gt; 0.34); t3 (35.3 ± 3.3 vs. 35.8 ± 3.1 hpi; p &gt; 0.28); t4 (36.3 ± 3.4 vs. 36.9 ± 3.7 hpi; p &gt; 0.20); t5 (47.9 ± 4.7 vs. 48.0 ± 4.8 hpi; p &gt; 0.88); t8 (54.0 ± 6.5 vs. 54.1 ± 6.5 hpi; p &gt; 0.91); tSB (86.3 ± 14.6 vs 85.7 ± 15.5 hpi; p &gt; 0.78) and tB (93.0 ± 16.9 vs. 93.2 ± 17.2 hpi; p &gt; 0.94). These findings suggest that the timing of key developmental events does not vary between male and female ICSI-derived preimplantation embryos.

Limitations, reasons for caution
The main limitation of this study is its retrospective nature and sample size. We analyzed the data of embryos leading to a live birth; therefore, caution is warranted when generalizing results to non-implanting embryos.

Wider implications of the findings
Male and female human embryos display similar morphokinetic patterns throughout preimplantation development in our study. Accordingly, embryo selection in a timelapse setting based on developmental characteristics does not bias sex ratios in resulting live births.

Trial registration number
not applicable