Abnormal cleavage up to Day 3 does not compromise live birth and neonatal outcomes of embryos that have achieved full blastulation: a retrospective cohort study

Abstract

STUDY QUESTION Do embryos displaying abnormal cleavage (ABNCL) up to Day 3 have compromised live birth rates and neonatal outcomes if full blastulation has been achieved prior to transfer? SUMMARY ANSWER ABNCL is associated with reduced full blastulation rates but does not impact live birth rates and neonatal outcomes once full blastulation has been achieved. WHAT IS KNOWN ALREADY? It is widely accepted that ABNCL is associated with reduced implantation rates of embryos when transferred at the cleavage stage. However, evidence is scarce in the literature reporting birth outcomes from blastocysts arising from ABNCL embryos, likely because they are ranked low priority for transfer. STUDY DESIGN, SIZE, DURATION This retrospective cohort study included 1562 consecutive autologous in vitro fertilization cycles (maternal age 35.1 ± 4.7 years) performed at Fertility North, Australia between January 2017 and June 2022. Fresh transfers were performed on Day 3 or 5, with remaining embryos cultured up to Day 6 before vitrification. A total of 6019 embryos were subject to blastocyst culture, and a subset of 664 resulting frozen blastocysts was included for live birth and neonatal outcome analyses following single transfers. PARTICIPANTS/MATERIALS, SETTING, METHODS ABNCL events were annotated from the first mitotic division up to Day 3, including direct cleavage (DC), reverse cleavage (RC) and <6 intercellular contact points at the 4-cell stage (<6ICCP). For DC and RC in combination, the ratios of affected blastomeres over the total number of all blastomeres up to Day 3 were also recorded. All pregnancies were followed up until birth with gestational age, birthweight, and sex of the baby being recorded. MAIN RESULTS AND THE ROLE OF CHANCE Full blastulation rates for embryos showing DC (19.5%), RC (41.7%), <6ICCP (58.8%), and mixed (≥2) ABNCL types (26.4%) were lower than the rates for those without ABNCL (67.2%, P < 0.01 respectively). Subgroup analysis showed declining full blastulation rates with increasing ratios of combined DC/RC affected blastomeres over all blastomeres up to the 8-cell stage (66.2% when 0 affected, 47.0% when 0.25 affected, 27.4% when 0.5 affected, 14.5% when 0.75 affected, and 7.7% when all affected, P < 0.01). However, once full blastulation had been achieved, no difference was detected between DC, RC, <6ICCP, and no ABNCL blastocysts following single frozen transfers in subsequent live birth rates (25.9%, 33.0%, 36.0% versus 30.8%, P > 0.05, respectively), gestational age (38.7 ± 1.6, 38.5 ± 1.2, 38.3 ± 3.5 versus 38.5 ± 1.8 weeks, P > 0.05, respectively) and birthweight (3343.0 ± 649.1, 3378.2 ± 538.4, 3352.6 ± 841.3 versus 3313.9 ± 509.6 g, P > 0.05, respectively). Multiple regression (logistic or linear as appropriate) confirmed no differences in all of the above measures after accounting for potential confounders. LIMITATIONS, REASONS FOR CAUTION Our study is limited by its retrospective nature, making it impossible to control every known or unknown confounder. Embryos in our dataset, being surplus after selection for fresh transfer, may not represent the general embryo population. WIDER IMPLICATIONS OF THE FINDINGS Our findings highlight the incremental impact of ABNCL, depending on the ratio of affected blastomeres up to Day 3, on subsequent full blastulation. The reassuring live birth and neonatal outcomes of ABNCL blastocysts imply a potential self-correction mechanism among those embryos reaching the blastocyst stage, which provides valuable guidance for clinical practice and patient counseling. STUDY FUNDING/COMPETTING INTEREST(S) This research is supported by an Australian Government Research Training Program (RTP) Scholarship. All authors report no conflict of interest. TRIAL REGISTRATION NUMBER N/A.

To Assess or Not to Assess: Reconsidering Day 3 Embryo Quality in Planned Freeze-All Blastocyst Cycles

“…One study assessing embryos with direct unequal cleavage (DUC) showed lower euploidy rates at the cleavage stage, but not at the blastocyst stage, and similar LB rates were observed if DUC blastocysts were transferred compared to non-DUC embryos [ 31 ]. Moreover, another recent study showed no negative impact on live birth and neonatal outcomes for blastocysts derived from abnormal cleavage embryos at day 3 [ 33 ].…”

The synergy of morphokinetic parameters and sHLA-G in cleavage embryo enhancing implantation rates

“…Embryos exhibiting abnormal cleavage indicate a possibility of implantation but minimal live birth. In a retrospective cohort study included 1562 consecutive autologous in vitro fertilization cycles, abnormal cleavage up to Day 3 is associated with reduced full blastulation rates but does not impact live birth rates and neonatal outcomes once full blastulation has been achieved ( Lee et al, 2024 ). In preimplantation genetic testing cycles, blastocysts demonstrating either direct or reverse cleavage should be biopsied, provided they meet morphological eligibility criteria.…”

Developmental perturbation in human embryos: Clinical and biological significance learned from time‐lapse images

“… 15 , 16 Embryos with direct and rapid cleavage exhibit lower rates of blastocyst formation and pregnancy after cleavage‐stage embryo transfers compared to embryos with normal cleavage. 56 , 57 , 58 The influence of direct and rapid cleavage on pregnancy outcomes after blastocyst transfers has been controversial. 57 , 59 , 60 , 61 However, a recent large cohort study concluded that direct cleavage does not impact the live birth rate once the embryo develops to the blastocyst stage.…”

“… 57 , 59 , 60 , 61 However, a recent large cohort study concluded that direct cleavage does not impact the live birth rate once the embryo develops to the blastocyst stage. 58 Therefore, the deselection of the embryos for transfer at the cleavage stage is recommended.…”