The Effect of Weight on Fertility and Pregnancy

The general health implications of maintaining normal weight have long been understood. People who are overweight experience a higher incidence of hypertension, diabetes, cancer and heart disease in addition to well-documented complications of pregnancy. More recently, studies have given us a better understanding of the effects of weight on fertility and fertility treatment. We will briefly review some of the considerations that make weight an important factor in the outcome of infertility treatment and pregnancy.

Both underweight and overweight women and men suffer from a higher incidence of infertility. Severe obesity in men has been shown to alter fertility often due to imbalances in hormone regulation tied to sperm production. In many cases, overweight or underweight women also may have hormonal disorders, which may cause them to ovulate infrequently or not at all. Generally, underweight patients (BMI less than 19) can be encouraged to gain more weight, and this alone often increases their fertility significantly or makes hormonal therapy more successful. On the other side of the spectrum, many studies have demonstrated a clear and consistent decrease in infertility with increasing female weight. Overweight patients who undergo significant weight loss may ovulate without the need for fertility medications. Ideal body weight results in the best outcome for fertility therapy and outcome for both mother and baby. A useful reference is the American Society of Reproductive Medicine campaign “Protect Your Fertility” ¹ (www.protectyourfertility.com) which educates patients of four important factors affecting their fertility: cigarette smoking, increased reproductive age, sexually transmitted diseases, and decreased or increased body weight.

Calculating your optimal weight

A recent American College of Obstetrics and Gynecology (ACOG) Committee Opinion ² states that patients should be weighed and have their heights measured at their initial visit and that comprehensive measures be discussed if the patient is overweight. It is surprising to many patients what weights are medically considered overweight, obese and extremely obese. According to the prestigious Institute of Medicine, obesity is defined by a measure calculated by the height and weight of the patient to give the body mass index or BMI. Normal BMI is defined by an index of less than 25; overweight patients are defined by a BMI 25 or greater; obesity is defined as Class I obesity with a BMI of 30-34.9; Class II as BMI between 35-39.9 and Class III as BMI 40 and above. You can determine your BMI by using the online BMI calculator: http://www.nhlbisupport.com/bmi.

Examples of what weight converts to what BMI for some average heights

	Normal	Overweight	Obese	Extreme Obesity
	BMI 19-24	BMI 25-29	BMI 30-35	BMI 40-54
5' 0''	93-123 lbs	128-149 lbs	154-200 lbs	205-277 lbs
5' 3''	107-135 lbs	141-183 lbs	189-220 lbs	225-304 lbs
5' 7''	121-153 lbs	159-185 lbs	191-249 lbs	255-314 lbs
5' 10''	133-167 lbs	174-202 lbs	217-272 lbs	279-377 lbs

Normal BMI optimizes fertility treatment success

As mentioned, there are numerous potential complications for obese women trying to get pregnant. Some of these include :

1. Lower response to medication used to regulate or initiate ovulation.
2. Greater need for carefully titrated dosing of medication, especially in patients with polycystic ovaries (PCO).
3. Greater frequency of over-response and the risk of over-stimulation and / or multiple pregnancies in response to medications used to induce ovulation. And if a multiple pregnancy is conceived, there are greater obstetrical complications in patients with excessive BMI than in multiple pregnancies in patients with a normal BMI.
4. More complicated IVF cycles (besides those complications listed above) including :
   • Fewer eggs retrieved
   • Greater technical difficulty retrieving eggs with greater risk of bleeding or injury
   • Greater anesthesia risk at the egg retrieval, including maintaining adequate airway, hypertension and aspiration ^{4 , 5}
   • Greater difficulty with embryo transfer in visualizing the uterus and accomplishing the embryo transfer effectively
   • Lower embryo implantation rates ⁶
   • Lower IVF success rates ^{6 , 7}
5. For those who do conceive, greater complications of pregnancy exist including :
   • Higher frequency of early pregnancy loss (miscarriage)
   • Greater anesthesia and surgical complications if any surgery required (e.g. D&C for miscarriage)
   • Greater frequency of hypertension, gestational diabetes, pre-eclampsia, stillbirth and other complication of pregnancy. ^{8 , 9 , 10} (Rates of stillbirth are twice as high in obese patients compared to normal weight patients)
   • Increased risks of requiring caesarean section delivery. The caesarean section rate is almost 50% in obese women and the postoperative complications following C Section - including pulmonary emboli and wound infection are significantly higher. ⁸
   • Due to larger babies, there is a greater delivery complication rate for those delivering vaginally. ⁹

BMI guidelines at SGFC

Our goal at Shady Grove Fertility Center is to provide you with the best and safest outcome possible. And, just as serious medical conditions like diabetes, hypertension or cardiac disease require treatment before embarking on fertility therapies, so should marked obesity.

Some Scandinavian countries have limited fertility therapy to women with a BMI <30, while the ACOG and many fertility centers in the United States utilize a BMI of 35 as a cut off for initiating fertility therapy. Our view at Shady Grove Fertility is that, while risks certainly exist at elevated BMIs at or around 35, and weight reduction should certainly be undertaken at these levels, the risks continue to increase substantially at BMI at or above 40 for IVF (with its greater need for anesthesia and surgical complications) and a BMI at or above 44 for any patients conceiving through fertility therapy. Therefore, at Shady Grove Fertility, patients must have a BMI less than 40 before initiating an IVF cycle and a BMI less than 44 before initiating IUI cycles.

Your doctor will discuss with you the importance of your weight as part of the overall review of your medical records and history. We will use this information and, when necessary, we will have a discussion on the serious impact of being underweight or overweight on your general health as well as your fertility care. We will encourage, or, as necessary, require a program of weight loss combining dietary modification as well as an exercise program prior to embarking on fertility therapy and conception.

References