Influence of body mass index (BMI) on the outcome of 6,827 IVF cycles

Abstract

Previous studies have noted that extremes of BMI confer to the IVF patient significant reductions in both implantation and pregnancy rates. A 60% differential in pregnancy rate between very obese (BMI = 35 kg/m2) IVF patients and IVF patients with a moderate BMI (BMI = 20–24.9 kg/m2) has been observed, even when controlling for factors known to affect the outcome of ART. A similar reduction in pregnancy rate of 50% has also been observed between underweight (BMI < 20 kg/m2) IVF patients and those with a moderate BMI. Despite these analyses, additional studies have failed to note differences in pregnancy rates among these groups of patients. The aim of our study was to utilize our large IVF-ET database to further define the relationship between IVF success and extremes of BMI. Retrospective. We reviewed 6,827 fresh non-donor IVF cycles at Boston IVF in which the BMI had been recorded. Patients at Boston IVF with a BMI > 40 kg/m2are not allowed to cycle. Cycles were divided among 5 BMI groups: I: <20 kg/m2, II: 20–24.9 kg/m2, III: 25.0–29.9 kg/m2, IV: 30–34.9 kg/ m2, and V: = 35 kg/m2. Characteristics of the cycles were compared. Differences among the groups were evaluated by one-way ANOVA using BMI as the classification variable. The chi square test was used to determine if there was an association between BMI and clinical pregnancy. 980 (14.4%) cycles were cancelled prior to hCG injection. In the 5,847 non-cancelled cycles there was no significant difference with respect to the number of mature follicles, number of oocytes retrieved, number of mature oocytes, cycle number per patient, and number of embryos transferred among the BMI groups (Table 1). The mean age was significantly lower among cycles in BMI group V (35.17 years) compared to all other BMI groups (p<0.0001)a. The mean peak estradiol (pE2) was significantly higher in BMI group I (1423.9 pg/ml) compared to the three highest BMI groups (p<0.0001)b. A BMI of > 35 kg/m2(V) was associated with a significantly lower implantation rate (13%, p< .0001)c and clinical pregnancy rate (21.75%, p<.0001)d compared to all other BMI groups. Despite a trend toward lower implantation and pregnancy rates with increasing BMI, the rates among the 4 lowest BMI groups were not significantly different. Table 1. Characteristics of IVF cycles by BMI group. Mean values are shown unless otherwise specified. A retrospective analysis of 6,827 IVF cycles determined that severe obesity, defined as a BMI = 35 kg/m2, is associated with statistically significant reductions in implantation and clinical pregnancy rates. In contrast to other studies, the patients with the lowest BMI had the highest success rates. The efforts of clinicians to optimize patient weight profiles prior to IVF are supported by this analysis.