Body mass index as a factor influencing oocyte competence and implantation potential – distribution and results in 4,882 women undergoing fertility treatment

Abstract

Introduction: The large amount of excess adipose tissue affects negatively every single step of the assisted reproductive treatment process – from the controlled ovarian hyperstimulation (COH) to obstetric complications and health consequences for the fetus. A number of scientific data show correlation between impaired clinical pregnancy rates (CPR) and obese patients maintaining high body 
mass index (BMI). The debate whether high proportion of body fat negatively affects oocyte quality or only impacts endometrial receptivity remains open. Aim: The aim of this study is to investigate the specific effect of the different BMI range in patients 
undergoing assisted reproductive technology (ART) treatment with reference to oocyte quality, fertilization capacity and implantation potential. Materials and methods: We analyzed a total of 4,882 women from partner couples who underwent ART treatment. Height and weight data were entered at the start of the in vitro fertilization (IVF) procedure. According to their BMI the female patients were divided in four distinct groups: in group 1 (underweight and BMI below 18.5 kg/m2) – 498 women, group 2 (normal range from 18.5 to 24.9 kg/m2) – 3021 women, group 3 (overweight with BMI between 25 – 29.9 kg/m2) – 789 women and group 4 (obese with BMI over 
30 kg/m2) – 484 women. Results: Distribution of the women in different BMI groups indicates that most of the Bulgarian patients undergoing fertility treatment are in the normal range. No association between BMI and ovarian response was found. A total 
of 33,205 oocytes were obtained after the COH. The mean numbers of the retrieved oocytes were similar (6,85 in group 1; 6,83 in group 2, 6,77 in group 3 and 6,67 in group 4) per woman and the fertilization rate was comparable in the four groups as it varies between 74-75%. Proportional categories of good, fair and bad embryos at cleavage stage were found. On the contrary, according to CPR, statistical difference between normal weight group (34,38%) versus overweight (29,6%) and obese groups (28,80%) (p < 0,05) was found. Conclusion: No correlation was found between the number of the retrieved oocytes and BMI values. Statistically lower pregnancy rates were reported in overweight women with BMI ≥ 25 kg/m² group and further onwards in the obesity group (BMI ≥ 30 kg/m²), which may be associated with impaired endometrial receptivity as a result of abnormally high levels of adipose tissue.