Pregnancy workouts are important for a healthy pregnancy, but how does a mother-to-be know when she’s overdoing it? Like in the case of exercise and fertility, there are many outdated ideas that muddy the waters about exercise during pregnancy. Unfortunately, many of these outdated ideas cause needless anxiety and confine pregnant women to essentially sit still until childbirth. Coupled with other myths, like the one that mothers should “eat for two,” inactivity can put mothers at increased risk for gestational diabetes, high blood pressure, and obesity.
On the other hand, there is some concern that overly strenuous exercise might cause fetal distress or complicate delivery. Due to ethical difficulties that make it harder to study pregnant women, unfortunately there isn’t a lot of evidence for exactly what the negative impact of intense exercise is on pregnant women. But based on the limited evidence we have, there are reasonable concerns about exercise beyond a certain intensity level for pregnant women1.
So, how much should pregnant women exercise? The answer is that it depends. This post will give you the tools you need, based on real scientific evidence, to answer that question for yourself.
Can I exercise during pregnancy?
Let’s settle this myth first: YES, you can exercise while pregnant unless specifically advised against doing so by your doctor. The current guidelines from American College of Obstetricians and Gynecologists recommend that pregnant women without obstetric complications exercise daily for at least 30 minutes. Most pregnant women without special concerns can safely incorporate 30 to 60 minutes of low-intensity walking into their daily routines.
It’s still a good idea to discuss exercise with your doctor during prenatal appointments, in case there are any special concerns with your pregnancy. Obstetric complications cover many different conditions (see full list of complications here). For women experiencing these complications, it is important to work with a doctor to create a safe and well-monitored exercise regimen that reasonably increases blood circulation without causing strain or increasing risk for other complications.
If your doctor clears you for exercise, there are still some things to be mindful of when exercising during pregnancy:
- Bring water when you exercise and keep hydrated before, during, and after exercise.
- Calorie intake. The goal of exercising while pregnant is to be healthy, not to lose weight. Pairing good exercise with good nutrition is important. Regardless of whether you exercise, your body simply need more calories to support a healthy pregnancy. If adding exercise, be sure to replenish calories with healthy foods.
- Low blood sugar. The body uses sugar (or glucose) from the blood as fuel when you exercise. Depending on how long and intensely you exercise, there is a risk of exercise depleting blood glucose, which can lead to dizziness, feeling faint, and cold sweats. Pregnancy hormones play a complex role in directing blood glucose to the uterus to support fetal growth and adding exercise may increase likelihood of low blood sugar. To prevent this, be sure to not skip any meals or snacks. Also, bring a snack when exercising in case you begin to feel light-headed. Good snacks to keep blood glucose levels in check have both carbohydrates and proteins, like apple slices with peanut butter or cheese and crackers.
- Supine position. It is also recommended that women avoid pregnancy exercises that involve laying flat on the back to prevent pressure on the vena cava; too much pressure on the vena cava can result in poor blood flow, dizziness, and low blood pressure (1).
- Heart rate & exhaustion. Check out the next section on target heart rate zones, which vary according to fitness level and age.
I’m really healthy and fit. Can I safely do pregnancy workouts that are more intense than walking?
Women who are already highly active before pregnancy are encouraged to continue their active lifestyles and exercise during pregnancy. This brings us to another myth: “pregnant women should keep their heart rate below 140 bpm.” This myth is problematic because pregnancy increases resting heart rate but also reduces how much heart rate can increase in response to intense exercise2. (2).
During pregnancy, women experience approximately a 50% increase in blood volume, and a significant amount of that blood is directed to the uterus to support fetal growth. This leads to a resting heart rate that is about 10 – 20 bpm higher, because the heart is working harder to make sure all the extra blood is circulating throughout the entire body while also incorporating the new, major detour to the uterus. Breathing rate is also increased during pregnancy, due to the hormone progesterone3..
When a pregnant woman is exercising intensely, the heart must work even harder to ensure proper blood circulation, and breathing rate is even faster to try to expel carbon dioxide. This means that if you try to keep up the same level of very intense exercise that you were able to handle before pregnancy, there could be serious effects such as dehydration, dizziness, and falling faint (and falling could hurt you and your baby).
How these pregnancy-related changes affect heart rate differs from woman to woman depending on her age and how fit she was before pregnancy. For these reasons, here are more up-to-date guidelines around safe intensity levels for exercise during pregnancy (3):
For healthy women (pre-pregnancy BMI < 25)
- 20 to 29 years old
- Low fitness background = 129 – 144 bpm
- Active background = 135 – 150 bpm
- Fit background = 145 – 160 bpm
- 30 to 39 years old
- Low fitness background = 128 – 144 pm
- Active background = 130 – 145 bpm
- Fit background = 140 – 156 bpm
For women with pre-pregnancy BMI > 25
- 20 to 29 years old = 102 – 124 bpm
- 30 to 39 years old = 101 – 120 bpm
Do you need to track your heart rate during exercise? No. A much simpler and equally effective solution is to track your perceived exertion using the “talk test”—checking that you can still talk or have a conversation during exercise. While it is not the most scientific test, it accurately tracks how taxing exercise is on respiration while still accounting for the fact that exertion varies from woman to woman depending on many factors.
Achieving a moderate level of intensity during pregnancy workouts is great for keeping the lungs and heart healthy, and how much intensity your heart and lungs can handle depends on how fit you were before pregnancy (4). Checking in periodically during your exercise routine with the talk test ensures that exercise is not too straining.
Here are a few signs that you should immediately stop exercising (1): dizziness, shortness of breath, headache, vaginal bleeding, amniotic fluid leakage, chest pain, calf pain or swelling, signs of preterm labor, and decreased fetal movement. Check with your doctor if these signs arise, and make sure to listen to your doctor’s advice about if and when it is safe to exercise again.
If I didn’t exercise before I got pregnant, is it safe to start during pregnancy?
Of course, some women who are not active before pregnancy may be concerned about how risky it is to suddenly start exercise during pregnancy. A clinical trial from 2016 showed that for previously inactive women, early pregnancy workouts reduced risk for obesity and hypertension and did not compromise infant outcome (5). In fact, current clinical guidelines indicate that as long as there are no pregnancy complications, beginning to exercise during pregnancy is beneficial for the mother and infant (1).
With regards to exercise intensity, it is recommended that these women begin with low intensity exercises and then work up to moderate intensity. Aerobic exercises that are considered safe as pregnancy exercises include dance, swimming, and leisurely walking (6). Athletic activities such as contact sports are not considered safe as pregnancy exercises.
- For women who are already active before becoming pregnant, continue exercising.
- For women who want to begin being active and are pregnant, start exercising slowly.
- For women with complications and risk factors, talk to your doctor first about incorporating pregnancy workouts that are safe.
- Exercise of moderate intensity has been linked to reduced risk for preterm birth (7). One study found that an intense bout of exercise does not appear to bear significant risk on fetal heart rate, although maternal age is an important moderating factor (8). However, a clinical review of studies examining vigorous exercise found mixed results (9). One study specifically examined how strenuous exercise affected women of active and inactive fitness backgrounds and found that while most women and their babies were able to recover normally, a subset of highly active women had reduced uterine blood flow and fetuses had low heart rate (bradycardia) which raises concerns about vigorous or strenuous exercise (10) ↩
- Regular heart beat requires a balance between sympathetic nervous system (“fight or flight”) and the parasympathetic nervous system (“rest and digest”). During exercise, the sympathetic nervous system increases heart rate, and the parasympathetic nervous system normalizes heart rate back to resting level after exercise. However, pregnancy reduces how the magnitude of how active the sympathetic and parasympathetic systems can be, so it is important to keep in mind that target heart rates will be different during pregnancy (2) ↩
- Breathing exchanges oxygen and carbon dioxide and helps maintain pH balance in the blood. Because both exercise and pregnancy increase breathing rate, there is a risk that intense exercise during pregnancy alters the balance between oxygen and carbon dioxide and pH of the blood, so it is important to be mindful of breathing rate to reduce this risk ↩