P-209 Overweight and obese women have slower developing embryos and a lower rate of morphokinetic top-quality blastocysts compared to underweight and normal weight women
Authors: Blais I , Koifman M , Lahav-Baratz S , Younes G , Weiner-Megnazi Z , Oron G 
Published: June 2022

Study question

Does maternal body mass index affect embryo morphokinetics and the rate of top-quality blastocysts

Summary answer

Overweight and obese women had slower developing embryos and a lower rate of top-quality blastocysts compared to underweight and normal weight women

What is known already

Time-lapse monitoring (TLM) allows for a detailed collection of embryo morphologic and kinetic changes compared to traditional periodic daily assessments. TLM allows for continuous observation of the developing embryo in time intervals for dynamic assessment of embryo morphokinetics. This may overcome any potential and unnecessary environmental fluctuations in comparison to the removal of embryos from the incubator for traditional static morphologic evaluations. There is a continuing strive to assess what factors are involved in embryo morphokinetics. Previous studies found maternal weight (either being underweight or overweight) to possibly be a contributing factor to embryo kinetic development, with conflicting results.

Study design, size, duration

Embryos derived from GnRH antagonist ICSI cycles between July 2013-December 2020 were included. Embryo division timings and morphokinetic top-quality embryo rates were compared between underweight (&lt;18 kg/m2) normal weight (8.5–25 kg/m2) overweight (25–30 kg/m2 ) and obese (≥30 kg/m2) women. Top-quality embryos with the highest chance to implant were defined: tPNf &lt;24.08, t2&lt;26.6, S2&lt;0.9, t8&lt;56 hours post insemination (hPi) for cleavage embryos and t2&lt;26.6, S2&lt;0.9, t8&lt;56 and tSB&lt;96.6 hPi for blastocysts.

Participants/materials, setting, methods

Optimal time durations: time to polar body extrusion (tPB2), time to pronucleus fading (tPNf), cleavage timings (t2-t8), synchrony of the second and third cycles (S2 and S3), duration of the second cycle (CC2) time to start blastulation (tSB) were based on an in-house model including embryos with known implantation data (KID). Multivariate logistic regression analysis: age, type of gonadotrophins, number of oocytes aspirated and peak estradiol levels was performed. Pregnancy rates were calculated from transfers.

Main results and the role of chance

We analyzed 1,953 embryos derived from 705 GnRH-antagonist ICSI cycles; 123 embryos from 43 cycles of underweight women, 888 embryos from 319 cycles of normal weight women, 517 embryos from 186 cycles of overweight women and 425 embryos from 157 cycles of obese women. Mean BMI was 17.3 kg/m2for underweight women, 21.8 kg/m2 for normal weight, 26.6 kg/m2 for overweight and 33.8 kg/m2 for obese women. Maternal age, gravidity and parity were similar between the groups. Pregnancy rates were similar between the groups. Overweight and obese women had a statistically significant longer mean time across cell stages t5-8 and tSB compared to underweight and normal weight women. Overweight and obese patients had the lowest rate of top-quality blastocysts (10.9% and 13.4% respectively) compared with underweight and normal weight women versus (33.9% and 20.1%, respectively), p = 0.0003. Top-quality blastocyst rates remained lower in overweight and obese women after adjusting for maternal age, type of gonadotrophins, number of oocytes aspirated and peak estradiol levels.

Limitations, reasons for caution

The strengths are a single center study with embryos cultured under the same standardized laboratory conditions and a relatively large number of embryos in each group. Only GnRH-antagonist ICSI cycles were included to standardize the protocol and control for fertilization time. The retrospective nature of the study is a limitation.

Wider implications of the findings

Developing an in-house model for morphokinetic parameters is an important additive tool for improving embryo selection and assessment of embryo quality. Finding patient characteristics that influence morphokinetic embryo quality are important in further improving IVF success rates.

Trial registration number

None