Too Much of a Good Thing?

Hi Mamas,

My question is about exercise during pregnancy: how much is too much? I have always been a very intensive exerciser before my pregnancy and have slowed down a little during my pregnancy. I’m 34 weeks and recently found out that my baby is measuring a little on the small side (34th percentile) and my dr says I’m not gaining enough weight at this stage of pregnancy. I’m eating a healthy diet with plenty of calories.

To give you some background, I was very fit but in the high end of the normal weight range before getting pregnant, and then gained 15 lbs in the 1st few months. I stopped running at around 27 weeks because it was giving me terrible hip pain. So now I’m power walking on an incline, using the elliptical and bike, as well as swimming & weights. I exercise for 1 hr 6 times a week at moderate to moderate high intensity. My heart rate is usually between 155 and 170 and I am 30 yo. Is this too much? I don’t get dizzy or feel out of breath so is there other warning signs I should look out for? I’ve done a lot of research on this subject and can’t seem to get a proper answer. Even my OBGYN doesn’t have any definite answers or advice. I would greatly appreciate your opinion.

Thank you,

Thank you for the great question, Maria.
You’re right; it’s one of those areas without a black and white answer. While exercise during pregnancy is perfectly healthy, and an important part of overall fitness and preparation for delivery, your heart rate target of 170 may be a bit high for the third trimester. The physiologic reasoning is that when you reach that heart rate you may be flirting with anaerobic metabolism, rather than aerobic, which may mean that your baby and the placenta aren’t getting as much blood flow as is optimal. Here is a chart of heart range zones modified for pregnancy.
Table 1. Modified heart rate target zones for aerobic exercise in pregnancy
Maternal age (years) Heart rate target zone (beats/minute)
<20 140-155
20-29 135-150
30-39 130-145
>40 125-140

More important than exact heart rate is your level of PE, or perceived exertion.Trust and listen to your body and take it down a notch if you’re feeling lightheaded, too hot, dehydrated, or experience cramps or discomfort.

Be sure and drink plenty of fluids, before, during, and after a workout. Try taking it down a notch and see if your weight gain picks up. And put aside those back-of-the-mind fears about gaining too much. You’ll need a reserve for the months of breastfeeding to come.
Congratulations! We wish you a speedy and painless delivery and a lifetime of learning with your little one.
~ The Mamas



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Rachel Zahn, MD is a pediatrician turned health writer who had three kids during medical school and pediatric training—crazy, huh?

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One response to “Too Much of a Good Thing?”

  1. Gigi

    Why not temporarily swap out few sessions of elliptical with a slower paced walk? Just till the weight goes up again.

    Gigi (I had IUGR with the first pregnancy, that’s the only reason I rested a lot in the second one)

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