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Increased body mass index is a risk factor for poor fertilization among women undergoing in vitro fertilization (IVF)

      Objective

      The effect of body mass index (BMI) on the outcome of assisted reproductive technology has been controversial. Many studies have found an association between BMI and poorer infertility treatment outcomes; however, the pathophysiological effect of an increased BMI on oocyte quality and fertilization has not been fully elucidated. We aimed to evaluate whether increased BMI is associated with the risk of poor fertilization in women undergoing in vitro fertilization (IVF).

      Design

      Retrospective cohort study from a large academically-affiliated infertility clinic.

      Materials and Methods

      Data were collected from women undergoing their first fresh IVF cycle from January 1, 1995 through April 15, 2012. BMI (kg/m2) was defined as the following categories: <18.5 underweight, 18.5-<25 normal, 25-<30 overweight, 30-<40 obese, and ≥40 morbidly obese. Poor fertilization was defined as having fewer than three mature oocytes normally fertilized; normal fertilizations were considered those with two pronuclei. Multivariate logistic regression was used to examine the relationship between poor fertilization and BMI.

      Results

      There were 13,807 first fresh IVF cycles performed. The number of normal fertilizations following IVF ranged from 0 to 42, with 28.1% of cycles experiencing poor fertilization. The following variables were controlled for: age, number of mature oocytes, year in which the cycle was performed, whether any manipulations such as intracytoplasmic sperm injection or assisted hatching were used, diagnosis of male factor infertility, and peak estradiol. After controlling for the above variables, compared to women with normal BMI, the odds (95% CI) of poor fertilization were 1.11 (0.50–2.50) among underweight women, 1.20 (1.03–1.40) among overweight women, 1.37 (1.15–1.64) among obese women, and 1.18 (0.78–1.77) among morbidly obese women.

      Conclusion

      Overweight and obese women undergoing IVF are at significantly increased risk of poor fertilization.