P-208 Culture media affect gender after IVF treatment: A detailed analysis of explanatory variables
Authors: Guldager T , Gabrielsen A V , Hedegaard Iversen L , Kierkegaard K S 
Published: June 2023

Abstract

Study question
Does embryo culture media affect gender at birth and why?

Summary answer
More male children were born after culture in the Sage 1-Step media compared to the G-TL media.

What is known already
ART increases the proportion of male children at birth. Laboratory techniques and culture conditions is known to impact secondary sex ratio (SSR). Physiological development differs in male and female embryos, leading to different metabolic requirements at the preimplantation stage. The composition of commercial culture medias varies and thus, the different medias may have different impact on embryo development and quality according to gender. This, in turn, may influence SSR, as embryos are selected based on morphological scoring systems and developmental speed.

Study design, size, duration
The study was designed as a retrospective registry-based study with all data collected at a single clinic. All embryos resulting in live birth from frozen and fresh single blastocyst transfers, in the period from 1. January 2017 to 31. December 2020 were included. Donor embryos and embryos cultured in more than one culture media were excluded. A total of 1371 SET embryos were included.

Participants/materials, setting, methods
Embryos were cultured in either the G-TL media, Vitrolife (n = 686) or the Sage 1-Step media, Origio (n = 685). All embryos were monitored for 5-6 days in a time-lapse incubator, Vitrolife, before single blastocyst transfer. Multivariate logistic analysis of cycle and embryo characteristics was performed to identify all factors associated to sex. The association between culture media and embryo morphokinetic according to sex was evaluated using a mixed model analysis.

Main results and the role of chance
Significantly more male singletons were born after culture in 1-Step media compared to G-TL media (risk ratio (RR) 1,1 95% CI [1,0, 1,3], P = 0,01). The female/male ratio was 42,3/57,7% in 1-Step media and 48,5/51,5% in G-TL media. The multivariate regression analysis displayed a higher chance of a male child with higher expansion grade (grade 5) (RR, 1,2 95% CI [1,0, 1,4] P = 0,04), lower inner cell mass grade (grade B) (RR 1,13 95% CI [1,0, 1,3] P = 0,02) and second embryo transfer (RR 1,2 95% CI [1,0, 1,3] P = 0,03). Trophectoderm (TE) grade B reduced the probability of male child compared with TE grade A (RR 0,8 95% CI [0,8, 0,9] P &gt; 0,05).
Male embryos developed significantly faster in the 1-Step media compared to the G-TL media for the stages of; blastocyst (tB) (-1,1 hours 95% CI [-2,1, -0,1]), expanded blastocyst (tEB) (-1,3 hours 95% CI [-2,3, -0,3]) and hatched blastocyst (tH) (-1,7 hours 95% CI [-3,0, -0,5]). Timing of development were the same for female embryos in the G-TL media compared to the 1-Step media. There was no significant difference in timing of development between female and male embryos in identical culture media.

Limitations, reasons for caution
This study was a retrospective study with data collection from only a single clinic, and as such in risk of confounding. Apart from culture media, culture conditions were similar during the two time periods. Paternal factors and type of infertility was not included.

Wider implications of the findings
Our observations suggest that culture media impact male embryo quality selectively, thus favoring selection of male embryos. As the impact appears to vary between different culture media, and has a measurable impact on gender after birth, the influence of culture media on embryo quality deserves more attention.

Trial registration number
not applicable