Weight is a sensitive subject for everyone, but for those trying to conceive, it is important to review and understand its impact on fertility and pregnancy. Being either underweight or overweight can make it more difficult to get pregnant, decrease success rates with fertility treatments, and lead to complications in pregnancy. However, you can optimize your chances for a healthy baby by learning more about the impact weight can have on fertility and taking steps to reach a healthier weight.
Body mass index (BMI) is a simple calculation based on height and weight. While not perfect for predicting health, it’s an easy way to study and compare the impact of weight on health and is used in most scientific studies. (You can calculate your BMI here). The World Health Organization established the following categories of weight based on BMI in 2004 (1):
Underweight if BMI <18.5 kg/m2
Optimal weight if BMI 18.6-24.9 kg/m2
Overweight if BMI 25.0-29.9
Obese if BMI >30.0 kg/m2.
By this definition, in the United States, 50% of reproductive-age women are overweight (2) and 37% of all adults (men and women) are obese (3).
Being overweight impacts overall health by increasing risk of hypertension, diabetes, cardiovascular disease, sleep apnea, osteoarthritis, cancer, and overall mortality (4). The impact of weight on fertility can often be overlooked because couples seeking help to conceive can be young and the effects of these chronic conditions may not yet be evident.
Anyone seeking fertility treatment or trying to conceive should be aware of lifestyle factors that can influence chances of pregnancy, with or without treatment. Physicians often recommend quitting smoking, limiting alcohol, sleep hygiene, and self-care, but they often leave out the weight discussion. Weight is a difficult and sensitive subject to bring up to a couple who is already struggling with another difficult and sensitive subject: infertility. But we cannot ignore the weight discussion if we really want to help patients conceive and bring a healthy baby to term. Optimizing weight can empower patients to increase their chances of pregnancy, with or without fertility treatment, and improve the chances of a healthy pregnancy and baby!
Here are the facts:
Weight Impacts Fertility for Women
Being under or overweight can impact fertility in women in multiple ways:
1. Weight can influence menstrual cycles and ovulation. Some underweight women stop menstruating while some overweight women have very irregular menses and ovulation, which makes tracking cycles and attempting conception difficult. Studies show that women with anovulation who reach a healthy weight can start ovulating regularly and have a higher chance of conceiving naturally (5,6).
2. Weight can impact responsiveness to fertility treatment. Studies show that women who are overweight require higher doses of stimulation medication (at a greater cost to the patient) and have lower responses to medication for fertility treatment (7-11).
3. Weight impacts success with fertility treatment. Studies in both humans and animals undergoing IVF show poor egg quality, lower fertilization rates, and lower blastocyst formation (advanced embryos) as BMI increases (11,12). A systematic review of over 27 clinical trials showed that women with a BMI >25 kg/m2 have a 10% lower success rate with IVF compared to women with a BMI <25 kg/m2 (13).
4. Weight impacts the uterine environment and success with embryo transfers. One study in gestational surrogates showed a lower implantation rate in women with a BMI >35 kg/m2 compared to women with a lower BMI (14).
Weight Impacts Fertility for Men
Obesity has been associated with poor sperm parameters on semen analyses, but studies are conflicting on the impact of male obesity on fertility treatment and pregnancy outcomes:
1. Studies have shown lower sperm counts and poor sperm parameters in obese men (20).
2. Other studies have shown lower fertilization rates and blastocyst formation rates in obese men (21).
3. Some studies have shown a lower live birth rate and higher miscarriage rate in couples with obese men (21,22).
Weight Impacts Pregnancy Outcomes
Being an unhealthy weight can increase risks in pregnancy:
1. Being overweight is associated with an increased risk of miscarriage. Multiple studies including over 40,000 patients in analysis have shown the risk of miscarriage increases in women who conceive with a BMI >25 kg/m2 (15,16).
2. Being overweight increases risks for multiple pregnancy complications, including gestational diabetes, hypertension, preeclampsia, preterm delivery, stillbirth, cesarean or instrumental delivery, shoulder dystocia, fetal distress, early neonatal death, and small- as well as large-for-gestational age infants (17-19).
3. Obesity has been associated with higher incidence of multiple birth defects, including heart defects, neural tube defects, and more (2).
How Can You Optimize Your Weight?
Awareness is the first step, and by reading this information, you are taking a positive step forward. Absorbing all of this information at once can seem overwhelming, but knowledge is powerful. Not all couples with obesity will have the poor outcomes listed above, but fertility and pregnancy at an unhealthy weight carries more risks, and we all need to be aware of what these risks are.
If you are underweight, gaining weight with the help of a nutritionist can be key. If you suffer from an eating disorder and struggle with body image and weight gain, start by asking for help.
If you are overweight, here are some steps you can take to move towards a healthier weight:
1. Ask for help. There are many resources out there. Find the one that’s right for you. Some people like the accountability and group mentality of Weight Watchers while others appreciate a more private approach with a nutritionist/registered dietician or physical trainer.
2. Find a buddy. Try to find someone with similar goals and help each other out. There are different apps with groups that people can join to encourage each other to keep moving and stay on track towards goals.
3. Get a monitor. There are many brands out there and ways to keep track online or connect with others to keep track of goals.
4. Write things down. Get a nutrition and exercise journal and keep track of what you’re doing. When you see results – positive or negative – you’ll have something to review and learn from.
5. Set realistic expectations and goals. Goals that are unattainable (like losing 50 pounds in one month) will leave you frustrated if not met while setting and achieving attainable goals will give you the encouragement you need to move forward. If you are obese, try losing 10% of your body weight as a first step.
6. Stick with it. Don’t give up if you slip up. Don’t let one banana split or a day without exercise break your momentum. Tomorrow is a new day to start fresh towards your goals.
7. Be forgiving and allow yourself a break or a treat. Everything in moderation – even moderation. No one is perfect. If you allow yourself breaks and treats, it will be easier to stay on track and meet your overall goal.
8. No Quick Fix. No crash diets or extreme exercise regimens. These may give you fast results, but they are not sustainable and can often be the opposite of healthy. The key is to make sustainable, realistic changes in habits that you can maintain. Cutting out soda or juice can dramatically reduce calorie intake. Cooking more at home can dramatically reduce salt and trans-fat intake. Small, realistic steps can have the most impact.
9. Be patient. Getting to an unhealthy weight didn’t happen overnight, and getting to a healthy weight will not happen overnight either. Focus on being your best health - do not focus on a number on a scale.
What about significantly high BMI and surgical options for weight loss?
Bariatric surgery can help with weight loss by surgically restricting the stomach to limit diet intake and can be one option for weight loss. Nutritional deficiencies can result with these type of weight loss options due to limited absorption. Pregnancies can be healthy and successful after these procedures if nutritional status of the mother is monitored closely. Some research recommends waiting 1-2 years after surgery to conceive to avoid fetal exposure to rapid weight loss and nutritional deficiencies during that time (23) but other research finds reassuring outcomes with pregnancies within a year of the surgery (24). Ask your medical provider about options.
What about the time it takes to lose weight?
Changing lifestyle, diet, and exercise routines can benefit someone for a lifetime but actual, sustainable weight loss can take time. When you’re trying to conceive, time can be against you. Fertility potential, egg supply, and success rates with fertility treatment decrease with age and it can be incredibly frustrating to think about waiting for fertility treatment to lose weight, especially if the couple is older or the female partner has diminished ovarian reserve. The balance of weight loss and time to fertility treatment is an important discussion to have with your doctor and every situation is unique. Find the right balance for you with your care team.
Now you know the facts and you have the knowledge to move forward. Take this information in a positive way – don’t let your weight define you or defeat you. The ultimate goal is completing your family in a healthy way, and in the process, you can discover habits that lead to a healthier life with your family.
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2. Obesity and Reproduction: A Committee Opinion. Fertil Steril 2015;104:1116-26.
3. CDC National Center for Health Statistics data brief 2015 https://www.cdc.gov/nchs/data/databriefs/db219.pdf
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