Weight Impacts Birth Control Effectiveness

Compared to women of normal weight, women who are overweight or obese are more likely to become pregnant while taking birth control pills. A study published in January’s Obstetrics and Gynecology showed that 5% of overweight women (compared to 3% of normal weight women) became pregnant each year while on the pill.

According to researchers, the higher a woman’s BMI (body mass index- a relationship of height and weight), the greater her risk is of becoming pregnant while on the pill.

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One more reason to get fit this year! By losing just 5 or 10 pounds, you can significantly reduce your risk of an unintended pregnancy. Women with the lowest risk in this study weighed less than 165 pounds. By burning 500 calories per day (through diet and exercise) you can lose about 1-2 pounds a week.
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Member Comments

Good article. Report
I had several warnings and first hand accounts from people who had bad experiences with The Pill - later on, did some research and realized one of the 5 or 6 ways that it works was a type of targeted miscarriage or like an "abortion" without it being labeled as such... at least, that was how I was interpreting it as. So I chose not to go on the Pill. Then my first husband told me about the Natural Family Planning, after his first wife had all kinds of problems with the Pill... We used it successfully during the 4 years we were married to avoid pregnancy. I remarried and taught my husband about NFP and we used it both to prevent pregnancy and to choose when we were ready for it, and had a son. By that time, I was an older mom with weight issues and probably an underlying (undiagnosed) case of PCOS (though I wasn't aware of the term at the time.).

But I knew too many people who struggled with their weight in using the Pill, the various inplants, shots, whever... just didn't seem like it was worth the benefits... Report
Ive been on the nuvaring for almost a year and not matter how healthy i eat or exercise i am gaining weight like crazy. Report
what about the different birth controls that arent the pill? like the nuva ring or the shot? i use the nuva ring and have for two years and my bmi says im really obese and ive never had a problem. Report
First they tell us that fat women can't have kids because we're too fat, and now they tell us we're at a higher risk for pregnancy on birth control? Crazy, I say. Report
i believe this simply because there is more of our body. surely some of the pill will get absorbed into the access fat making the pill less effective. to combat the problem take 1 pill plus a tiny bit of another!. will this work! i wonder!. Report
I am sceptical of all studies until I see details, but as an RN I can tell you that fat cells store hormones. This fact is tied to an increase in certain types of cancer, so it's not such a streatch to believe that those fat cells could be storing a portion of the birth-control hormones meant to control ovulation Report
Sorry I don't believe any of these warped studies of like 16 people these people pump out. I agree with the idea that extra weight places a strain on the body that would be obvious to anyone. However, I actually at 20 got pregnant while on the pill and the doctor couldn't believe it until the blood tests. I was in great shape at the time and finished the Water Safety Instuctor PE class in college about a week before I delivered. Only problem I had was I couldn't swim deep enough to pick up the brick due to pregnancy. After my second child, a son, was born, i decided to research myself. Finally, I decided that the solution for me was a 1500 year old device but not in metal but plastic - the IUD. This device worked wonderfully for me for many years and I am now going through menopause without sweats and more drugs. Report
This is interesting. I've been on one or another birth control pill for many years, some of those years at a normal weight, some overwieght, and some obese. Never conceived. I guess I'm one of those weird stats - I don't fit the norm. Report
The sad fact of the matter is though, that you CAN (and usually do) gain weight while on the pill, and is thought to be a side-effect of using birth control. Especially with the kind of birth control that ensures that you *don't* have a period. I don't use birth control pills. We use OTC products just fine. No unplanned pregnancies, and no side effects. I'm fat right now because of ME! LOL! Report
I didnt know that...I weight 160 lbs and started using Evra after I got married (5 months ago). I have been gaining weight like crazy....do you know if that is a side effect? Report
For Ortho Evra (the patch) it's recommended that you not weigh over 195 pounds. My doctor did not tell me this when I went on it even though I weighed in just under 195 pounds at the time. Report
Great article. Pregnancy is a stress on the body without having the added burden of obesity. Report


About The Author

Nicole Nichols
Nicole Nichols
A certified personal trainer and fitness instructor with a bachelor's degree in health education, Nicole loves living a healthy and fit lifestyle and helping others do the same. Nicole was formerly SparkPeople's fitness expert and editor-in-chief, known on the site as "Coach Nicole." Make sure to explore more of her articles and blog posts.