Blastocyst formation is similar in obese and normal weight women: a morphokinetic study.

STUDY QUESTION

Does the embryo cleavage pattern and rate of blastocyst formation differ between normal weight and obese women undergoing IVF?

SUMMARY ANSWER

Embryo morphokinetic development, final blastocyst formation rate and blastocyst morphology do not differ between obese and normal weight women.

WHAT IS KNOWN ALREADY

Female obesity has been related to impaired IVF outcomes. Although the mechanisms responsible for this detrimental effect are thought to include impaired oocyte and embryo quality and reduced endometrial receptivity, they are yet to be confirmed. Embryo quality has been commonly assessed using static morphological criteria. Only three studies have analysed the progress of embryos up to the blastocyst stage in women with elevated BMI, but they have used small samples of patients or have obtained contradictory results.

STUDY DESIGN, SIZE, DURATION: This retrospective, cohort study, was performed from January 2016 to May 2020. A total of 3316 ICSI cycles from 2822 women were included, of which 1251 cycles were part of a preimplantation genetic testing programme. In total, 17 848 embryos were analysed.

PARTICIPANTS/MATERIALS, SETTING, METHODS: This study reports on the IVF cycles of infertile women, with a known BMI, who underwent ICSI and whose embryos were grown until the fifth/sixth day of development in a time-lapse system. Patients were grouped as follows. Underweight was defined as a BMI <18.5 kg/m2; normal weight was a BMI of 18.5-24.9 kg/m2; overweight was a BMI of 25-29.9 kg/m2; and obesity was a BMI of ≥30 kg/m2. Embryo development was assessed on an external computer with analysis software.

MAIN RESULTS AND THE ROLE OF CHANCE

Despite an initial slower pattern of embryo development, the blastocyst formation rate on day 5 or on day 5 plus day 6 did not differ in obese women with respect to the other three BMI groups. Moreover, based on the evaluation of inner cell mass and the trophectoderm on both days of blastocyst development, embryo quality was similar across the BMI groups, as were the pattern of development and arrest up to blastocyst formation and the distribution of the categories of full, expanded and hatching blastocysts.

LIMITATIONS, REASONS FOR CAUTION: Limitations include the retrospective analysis of data, the use of BMI as the only parameter to define normal/abnormal female body weight, and the lack of complete information about clinical outcomes.

WIDER IMPLICATIONS OF THE FINDINGS

Blastocyst formation and embryo morphokinetics are not affected by female obesity, and the poorer IVF outcomes described for such women are probably due to deficient endometrial receptivity. The role of endometrial progesterone exposure on the day of embryo transfer should be analysed in future studies as a possible determining factor.

STUDY FUNDING/COMPETING INTEREST(S): No external funding was used and there are no competing interests.

TRIAL REGISTRATION NUMBER

N/A.