The Effect of Weight on Fertility

Maintaining an ideal weight is something we know to be important for our overall health and well being, but what we have come to learn from studies is the direct effect of weight on fertility as well as the outcome of infertility treatment and pregnancy.

While often it is assumed the negative effect on weight on fertility is associated with being overweight, women who are underweight (BMI less than 19) may not be getting enough nutrients, which can cause their bodies to ovulate infrequently or not at all. In overweight women, an increase in insulin levels may cause their ovaries to reproduce male hormones and stop releasing eggs, which results in ovulatory dysfunction. With modest weight changes, both overweight and underweight women may resume ovulation on their own without the need for fertility medications.

For Men: The Effect of Weight on Fertility

Women are not the only ones who are affected by weight and fertility. Men suffer from similar complications, since being overweight or underweight causes changes in the body. Severe obesity in men has shown to impact fertility due to imbalances in hormone regulation tied to sperm production (low sperm count and motility, or sperm movement).

What is the ideal BMI if trying to conceive?

An ideal body weight can result in improved outcomes for both the mother and her baby. According to the Institute of Medicine, obesity is defined by a measure calculated by the height and weight of the patient to determine the body mass index, or BMI.

• Normal BMI
  • Defined by an index of less than 25
• Overweight
  • Defined by a BMI of 25 or greater
• Obesity
  • Defined by a BMI of 30-34.9 (Class 1 obesity)
  • Defined by a BMI between 35-39.9 (Class II obesity)
  • Defined by a BMI above 40 (Class III obesity)

You can determine your own BMI using the online BMI calculator found here.

Normal BMI Optimizes Fertility Treatment Success

When women are under or overweight, their BMI has been found to impair successful outcomes for fertility treatment. Some of the complications that can arise as a result of a high BMI may include:

• Lower response to medication used to regulate or initiate ovulation
• Greater need for carefully titrated dosing of medication, especially in patients with polycystic ovary syndrome (PCOS)
• In response to medications used to induce ovulation, women who are overweight or obese have a greater frequency of over-response and a higher risk of overstimulation and/or multiple pregnancies. If a multiple pregnancy occurs, there are greater obstetrical complications in patients with high BMI than in multiple pregnancies in patients with a normal BMI.
• More complications with in vitro fertilization (IVF) treatment
  • Fewer eggs retrieved
  • Greater difficulty retrieving eggs with increased risk of bleeding or injury
  • Greater anesthesia risk at the egg retrieval, including maintaining adequate airway, hypertension, and aspiration ^1,2
  • Greater difficulty with embryo transfer in visualizing the uterus and accomplishing the transfer effectively
  • Lower embryo implantation rates ³
  • Lower IVF success rates ^3,4

For those women who are overweight and get pregnant, there are increased risks of complications during pregnancy, which may include:

• Higher frequency of early pregnancy loss (miscarriage)
• Greater anesthesia-related surgical complications if any surgery is required (i.e., D&C for miscarriage)
• Greater frequency of hypertension, gestational diabetes, pre-eclampsia, still birth, and other pregnancy complications ^5,6,7
• Increased risk of requiring caesarean section delivery. The caesarean section rate is almost 50 percent in obese women ⁵
• Due to larger babies, there is a greater delivery complication rate for those delivering vaginally ⁶

It’s important to note, with all the potential complications and adverse effects, reduction in BMI through weight loss has been demonstrated to significantly improve fertility treatment success, lower complications of treatment, and lower complications of pregnancy.

BMI Guidelines for Treatment at SGF

At SGF, your physician will review your medical history and records at your first appointment to determine if there is any need for concern regarding BMI in order to begin treatment. He or she will also provide you with the appropriate resources—including recommendations for weight loss programs, nutritional counseling, dietary modifications, and/or an exercise regimen, if need be. The goal for both patient and physician should be for the patient to be in the best possible overall health before beginning treatment.

Editor’s Note: This post was originally published in December 2008 and has been updated for accuracy and comprehensiveness as of June 2016.

To learn more about the effect of weight on fertility or if you would like to schedule an appointment, please contact our New Patient Center at 1-877-971-7755. 
References for the Effect of Weight on Fertility: