PHILADELPHIA — Patients considering in vitro fertilization should be encouraged to aim for a healthy body mass index before they start treatment, results of a large retrospective study suggest.
“There was a trend toward decreasing success rates with increasing BMIs,” reported lead investigator David Ryley, M.D., of Beth Israel Deaconess Medical Center, Boston, and Boston IVF, a private fertility clinic.
The study reviewed more than 5,800 fresh, non-donor in vitro fertilization (IVF) cycles at Boston IVF in which the patient's BMI had been recorded, he reported at the annual meeting of the American Society for Reproductive Medicine.
Patients were divided into five groups according to BMI: under 20 kg/m
There was no difference between the groups with respect to the number of mature follicles, number of oocytes retrieved, number of mature oocytes, the number of cycles per patient, and the number of embryos transferred. Still, patients in the highest BMI category had a significantly lower implantation rate and clinical pregnancy rate, compared with the other BMI groups.
Although the clinical pregnancy rate ranged from about 27% to almost 33% in the lower BMI categories, it was not quite 22% in the highest BMI category.
Similarly, the implantation rate ranged from 18% to 20% in the lower BMI categories, but it was only 13% in the highest BMI category.
Unlike previous published studies on this topic, the current study did not find an association between extremely low BMI and poor IVF success rates, Dr. Ryley said.
“The best data in the literature suggest that severely low BMIs under 20, or under 18, affect the hypothalamic-pituitary axis, such that patients have irregular menstrual cycles and, therefore, have an impaired chance of fertility,” he told this newspaper. “But in our study the patients with the lowest BMIs actually had the highest pregnancy rates—although the difference was only significant when compared with the highest BMI category.”
The study's findings are consistent with other reports of how excess weight can impact hormonal balance and the quality of oocytes and embryos, he said. Weight loss can often correct problems such as hyperinsulinemia and polycystic ovarian syndrome, which can in turn increase fertility.
But physicians should also know how to manage an IVF cycle in an overweight patient who has not lost weight.
“We know that patients with high BMIs require higher doses of medications, particularly gonadotropins, to stimulate folliculogenesis, and they often require longer cycles,” Dr. Ryley said. “By increasing the doses of these medications, you can often get an adequate number of oocytes. However, in many of these patients, hormonal imbalances may have a deleterious effect on the quality of oocytes you get.”