How your weight affects your fertility and pregnancy

Your Ideal Baby Weight

You don’t need to achieve your dream body in order to get pregnant. Most women who consider themselves a little overweight or underweight can get pregnant without issue. But if your BMI is below 19 or above 24, you may have difficulty getting pregnant.

But BMI doesn’t always tell the full story. Even if your BMI is within the normal range, you still might have a weight-related fertility issue. For example, if you’re a weightlifter, your heavy muscles may put you on the higher side of the BMI scale, even though you don’t have excess body fat. And it’s possible to be thin, but still nicely padded with estrogen-producing body fat. Or you might be thin and athletic, with plenty of muscle, but hardly any fat. Even if you weigh the same as someone who’s thin and well-padded, you still might produce much less estrogen—which could disrupt your menstrual cycles and undermine your fertility.

Overweight & Fertility

Estrogen is produced primarily in your ovaries. But more than 30 percent of the estrogen in your body is produced by your fat cells. If you’re at a healthy weight, then chances are you’re producing a healthy amount of estrogen.

If you’re overweight, those additional fat cells will be producing more estrogen than necessary. If you have extra body fat, and extra estrogen, that must be a good thing for fertility, right? Unfortunately, it doesn’t work like that.

Too much estrogen can actually prevent you from ovulating regularly, or even ovulating at all. Thirty to 40 percent of obese women have irregular menstrual cycles, decreasing their chances of getting pregnant. And women who are severely obese (with BMIs ranging from 35-40), may be 23 – 43 percent less likely to conceive, compared with women who have a BMI of 29 or below.1

If you’re overweight but still have regular periods, you’re not necessarily in the clear. Studies show that women who are overweight have a harder time getting pregnant, even if they have normal periods.

Besides decreasing the chances of natural conception, obesity also impairs the success rates for fertility treatments. Once pregnant, obese women that got pregnant either through natural conception or fertility treatment have an increased risk of miscarriage and birth defects in babies.2 They are also at a risk of developing pregnancy induced diabetes and preeclampsia.3

Being overweight or obese is also associated with hormonal and endocrine conditions that can decrease fertility, including PCOS, insulin resistance, and excess testosterone.  

If you are overweight, losing weight could increase your chances of conceiving. A recent study from the Stanford School of Medicine was able to show that patients who achieved significant weight loss (10 percent of their maximum weight) had higher pregnancy and live birth rates in comparison to those women who did not achieve significant weight loss.4

Underweight

Women with very low BMIs—usually below 18.5, but the threshold can be higher or lower for some women—tend not to have regular periods. Irregular cycles means irregular (or non-existent) ovulation, which, to state the obvious, could make it very difficult to get pregnant.

Luckily, there’s a straightforward solution to this problem, though it’s one that many women will do almost anything to avoid: gain weight. If you’re underweight and not getting regular periods, this is the first thing you should try—before acupuncture, Chinese herbs, hypnosis, or anything else. Most of the weight you gain should be fat, not muscle (remember: fat produces estrogen), so don’t go replacing long runs with equally intense weight lifting sessions.  

Every body is different. There are naturally lean ladies who conceive with ease, and fit, healthy women who find it necessary to give up some of their fitness in exchange for regular cycles. Chances are, you’ll need to achieve a BMI of at least 18.5, and preferably 20 to 24, the range considered optimal for babymaking.

How do I find out if I have the right weight?

The BMI is used as a common indicator for the ration between weight and height. A normal and healthy BMI is between 19 and 24. If your BMI falls too far on either side of the spectrum (lower than 19 or higher than 24), consider evaluating your diet and eating habits to bring yourself into a better range for fertility.

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  1. Van der Steeg, J.W., Steures, P., Eijkemans, M.J.C., Habbema, J.D.F., Hompes, P.G.A, Burggraaff, J.M., Oosterhuis. G.J.E., Bossuyt, P.M.M., van der Veen, F., & Mol, B.W.J (2008). Obesity affects spontaneous pregnancy chances in subfertile, ovulatory women. Oxford Journals, 23 (2). Retrieved November 10, 2015, from http://humrep.oxfordjournals.org/content/23/2/324.full.pdf+html
  2. Metwally M., Ong KJ., Ledger W.L. and Li T.C. (2008 September). Does high body mass index increase the risk of miscarriage after spontaneous and assisted conception? A metaanalysis of the evidence. Fertility and Sterility 90(3):pp. 714-26.
  3. American Society for Reproductive Medicine. (2015). Weight and Fertility. Retrieved December 04, 2015, from https://www.asrm.org/FACTSHEET_Weight_and_Fertility/
  4. Kort, J.D., Winget, C., Kim, S.H. and Lathi, R.B. (2014, May). A retrospective cohort study to evaluate the impact of meaningful weight loss on fertility outcomes in an overweight population with infertility. Fertility and Sterility 101(5), pp. 1400-1403.
2017-01-04T22:47:56+00:00 By |Diet & Exercise, Preparing your Body|

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