Ideas about exercise in pregnancy have changed dramatically over the past 50 years. A generation ago women were often advised to be sedentary in pregnancy and the general fear was that exercise would harm the fetus or cause complications. Bedrest or “putting your feet up” was liberally prescribed as a treatment for many obstetric concerns.
Thankfully a large amount of scientific evidence has proven that staying active in pregnancy is not only safe, but is highly recommended for the vast majority of patients. We now know that in the absence of rare obstetric or medical complications, physical activity is safe and desirable in pregnancy and may prevent disease and improve outcomes. Pregnancy also provides an opportunity for adopting a healthy lifestyle even for women who have not previously been physically active, and beginning a moderate exercise regimen in pregnancy is highly recommended for previously sedentary women.
Current recommendations supported by the ACOG ( American College of OBGYN) are for healthy pregnant women to get at least 150 minutes of moderate intensity aerobic activity a week (with much more than that being safe for women who are already in good cardiovascular shape). Exercise is preferably spread thought the week (for example, 30-60 minutes 5 times a week).
Evidence shows that engaging in physical actively can reduce maternal weight gain, and even can reduce the risk to the fetus of childhood obesity. It also reduces the risk of gestational diabetes by 50-75 percent and may also reduce the risk of pregnancy induced hypertension (pre-eclampsia). Contrary to popular belief, moderate exercise does not increase the risk of miscarriage or preterm delivery in otherwise healthy patients.
A popular notion is that we should keep our heart rate under 140 beats per minute when exercising in pregnancy. This is an old piece of wisdom which is not based in science, and many studies have attempted to find the perfect heart rate for exercise in pregnancy without success. Goal heart rates for individuals vary based on physical conditioning, age, weight, temperature and other factors. To be in the recommended “moderate exercise” range, a heart rate of 120-140 will commonly be a good goal, but well conditioned women may have much higher heart rates and still be in the correct training zone.
A good rule of thumb is that when doing aerobic exercise, if you can “talk but not sing” you are in the moderate zone. The goal is to be slightly out of breath but not to the point where you are struggling. This can also be described as a “comfortable, conversational pace”. Generally if you follow these guidelines we do not recommend using a heart rate monitor, as the goal numbers are so variable between individuals.
Almost any exercise is safe in pregnancy with a couple of exceptions. Avoid exercise that puts you at high risk of falling or abdominal trauma, such as skiing, kick boxing, martial arts or vigorous horseback riding. Also avoid exercises after 16-20 weeks that involve lying flat on your tummy or spending prolonged periods flat on your back. Lying flat on your back for long periods in the third trimester can temporarily decrease blood flow to the uterus, which is easily avoided by tilting slightly to one side. Almost all exercises can easily be modified to avoid these positions.
While weight lighting has never been shown to be harmful to the fetus, our center of balance is altered during pregnancy and our joints become more lax, increasing the risk of muscular injury. So it is wise to be careful when lifting heavy weights and consider reducing the weight in order to maintain proper form and avoid injury.
The recommended maximum duration of exercise has not been established, and studies on athletes exercising for more than an hour daily have failed to show any harm. Mothers who exercise more intensely obviously have a lower total weight gain and their babies to be several ounces smaller than women who exercise normally, but this has not been shown to be harmful to mother or baby.
The normal physiologic changes of pregnancy dramatically change our cardiovascular and respiratory systems, significantly lowering our exercise tolerance in most cases. Even very fit women will find themselves unable to complete their normal routine without feeling tired and out of breath. It is important to listen to these changes in our bodies and take our exercise level down a notch or two to stay within the moderate exercise range described above.
Pregnancy is not a time that we are going to excel in exercise; the goal is to participate but not to excel! Since dehydration is associated with preterm contractions, it is important to stay well hydrated while exercising and to stop if pain or significant uterine contractions occur.
Certain rare patients should not exercise in pregnancy. Your provider will certainly discuss that with you in detail if you fall into one of these groups. Examples of patients who need to be sedentary in pregnancy are those with placenta previa, vaginal bleeding, incompetent cervix, preterm labor, pre-eclampsia or significant heart or lung disease.
After delivery, it has been historically common for patients to be told not to exercise for a certain period of time (for example, 6 weeks). There is no science to support delaying return to exercise for a prescribed period for all patients. Many patients can safely exercise within days after a normal vaginal delivery, and even after a C-section many patients can safely start moderate aerobic exercise in 2-3 weeks. Every patient’s situation is different and we can help to advise you on your individual situation after delivery.
While attempting conception, it is rare that our normal exercise regimen needs to be altered. Some women can exercise to the point at which body fat drops below 15 % (such as gymnasts, ballerinas and elite long distance runners) and this can compromise ovulation. When patients are excessively thin and are not having regular periods, their exercise regimen may need to be reduced in order to conceive. But for patient exercising regularly and having normal cycles, fertility will not be compromised by physical activity. More commonly ovulation disorders are related to being overweight, and in those cases exercise and weight loss can often restore normal fertility.
We hope this helps you to be confident about exercising in pregnancy. If you have questions about the best exercise regimen for you, please email your nurse or talk to your provider.
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