Adverse effects of obesity on natural conception and assisted reproductive therapy in women are well documented in the literature [5-8] (see Table 5.1). For example, Rich-Edwards et al.  found that, among ~2,500 married, infertile nurses, those with pregestational obesity experienced more frequent anovulation and had longer mean time to pregnancy than did normal-weight women. Also, higher rates of early miscarriage have been found among obese women as compared with women of normal weight. In a case-control study of 1,644 obese women compared with 3,288 normal weight, age-matched controls, Lashen et al.  found an increase risk of first trimester and recurrent miscarriage associated with pregestational obesity. Similarly, a Swedish population-based cohort study of over 800,000 women showed that obesity was associated with a twofold greater risk of spontaneous abortion compared with normal weight mothers .
Potential Reasons for Infertility in Obese Women
Menstrual irregularities Hyperandrogenism Oligo-/amenorrhea Chronic anovulation
Decreased conception rates after assisted reproductive techniques Increased risk of miscarriage
In overweight women conceiving after in vitro fertilization (IVF) or intracytoplasmic sperm injection, miscarriage rate is also reportedly higher in obese compared with lean or average weight women. A systematic review of the literature by Maheshwari et al.  found that when compared with women with a BMI < 25 kg/m2, women with a BMI > 25 kg/m2 had a 29% lower likelihood of pregnancy and a 33% higher risk of miscarriage following IVF. In this same study, obese women were found to have a reduced number of oocytes retrieved despite requiring higher doses of gonadotropins. Mechanisms for the relationship between obesity and infertility are unknown. Suggested roles of hyper-androgenism, insulin resistance, high leptin levels, and polycystic ovarian syndrome are currently under investigation . Regardless of mechanism, these data suggest that obesity may delay or prevent conception in women who want to become pregnant. Of some consolation, weight loss before infertility therapy may improve a women's likelihood of conceiving. Notably, over a dozen studies have documented improvement in reproductive parameters and fertility outcome following moderate weight loss [13-24].
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