Getting to the heart of your pregnancy: What cardiovascular changes you can expect
February 11, 2025
Carrying a baby changes a lot more than just your belly size. Your cardiovascular system – your veins, arteries, and heart – is changing alongside your hormones, expanding feet, and forgetfulness of “pregnancy brain.”
Hormonal changes start in the earliest days of pregnancy, kicking off a chain of events that requires your cardiovascular system to adapt. Your heart rate will increase, fluid will accumulate where it didn’t before, and by the end of pregnancy, your total blood volume will double – that’s a lot for your heart and blood vessels to take on!
All these changes are normal and temporary. They happen gradually, so you likely won’t notice them. After delivery, your cardiovascular system will return to its pre-pregnancy state within a month to six weeks.
But in some cases, abnormal changes such as very high blood pressure or heart valve problems can interfere with pregnancy – and have a long-term effect on your health. In these cases, UTSW maternal-fetal medicine specialists will join your pregnancy care team. These specialists work on complex pregnancies to help achieve the best outcomes for mom and baby.
Let’s talk through normal changes to expect during and after pregnancy and how to know when to seek specialized care.
Heart rate increases
By the time you’re eight weeks along, your resting pulse rate has increased by 10 beats per minute. You’re likely to see another increase between 12 and 16 weeks and again when you reach 32-36 weeks.
On average, pregnant patients have a heart rate of about 79 beats per minute at 10 weeks, rising to nearly 87 beats per minute at 40 weeks.
Blood pressure goes down … then up
When you first become pregnant, your body starts to pump out a hormone called progesterone to help keep the uterus relaxed. This hormonal change also causes your blood pressure to go down in the early weeks of gestation. It might lead to mild twinges of dizziness or weakness during your first or second trimester.
The downward trend in your blood pressure continues until around 24-26 weeks, when it starts to track upward again. It will continue to increase throughout the rest of your pregnancy.
Your provider will check your blood pressure at every visit and discuss the results with you. If it appears to be rising too high or too fast, it could be a sign of a potentially serious complication called preeclampsia, or gestational hypertension. This is a major cause of maternal stroke and kidney failure, and it can disrupt blood flow to the placenta. The only cure is delivery, and that might mean your baby is born prematurely.
Related reading: Preeclampsia: Spot high blood pressure symptoms during or after pregnancy
Total blood volume increases
To deliver oxygen and nutrients to your growing baby, your body will begin boosting your blood supply. There is a significant change in your blood volume when you’re about 10-12 weeks along. Throughout your pregnancy, your blood volume will nearly double! Most of the new volume will be made up of plasma, the liquid that carries blood cells and other substances throughout your body.
Cardiac output goes up
Cardiac output is a combined measurement of your heart rate and the level of “squeeze” your heart gives as it’s pushing your blood through to the rest of your body. The increased output begins at about five weeks’ gestation and will peak at a 30%-50% increase by 16-20 weeks of gestation. Then it levels out during the last half of your pregnancy and returns to normal not long after delivery.
If you’re expecting twins, your cardiac output will be about 15% higher than if you were expecting a single baby.
Your heart builds muscle mass
While the heart should not actually get bigger during pregnancy, it will build new muscle mass. Physicians and researchers call it “cardiac remodeling.” In some pregnant patients it can be similar to the changes observed in athletes!
My colleagues Robert Stewart, M.D., and David B. Nelson, M.D., conducted a study using MRI to measure cardiac remodeling. Their team found that the increase in blood volume, heart rate, and cardiac output causes a 30%-35% expansion in the muscles of the left ventricle of the heart. There is a significant increase in this measurement at about 26-30 weeks of pregnancy, and that expansion continues until delivery.
Changes that might need a closer look
A lot of what we know about the management of cardiovascular disease during pregnancy is outlined in Williams Obstetrics, a landmark reference book used by obstetricians and gynecologists around the world and authored by physicians at UT Southwestern Medical Center.
If you have other health testing while you’re pregnant, the provider might notice changes that, while common, are worth discussing with your pregnancy care provider.
Appearance or position of your heart
As your uterus grows, it shifts other organs aside to make room. This might show as a change in the axis of your heart or a slight shift in how it’s positioned within your chest on an EKG or chest X-ray.
Your heart can also appear a bit enlarged. It’s normal to have small amount of fluid accumulate around your heart during pregnancy, which can make the heart look larger. If you develop a persistent cough that worsens when you lie down, it might be a sign that excess fluid is building up around your heart or backing up into your lungs. Be sure to mention any symptoms like this to your physician urgently.
Heart murmur
Previously unnoticed heart murmurs are common in pregnancy. A murmur is the sound your blood flow makes as it moves within the heart if there is a difference in cardiac structure. Your increased blood volume can make this noise more pronounced.
If your provider detects a sound that’s unusual during pregnancy, they may recommend further tests to check for a problem with a heart valve or the septum, which is the wall of tissue that separates the two sides of the heart.
Heart palpitations
Increased cardiac output imposes a strain on your heart. This can sometimes irritate the electrical system that regulates your heartbeat. A palpitation can feel like a brief flutter, or it might seem like your heart is racing or you have an extra heartbeat. All of these are usually benign and dissipate quickly, but it is important to let your physician know if it is recurrent. If you feel any sudden pain, dizziness, or shortness of breath, contact your provider for evaluation.
Related reading: New mom survives SCAD heart attack: Hole in her heart
“If you begin to feel dizzy, sweaty, or weak as you lie on your back during an ultrasound, ask the provider if you can roll to your left side. Even a small tilt can get the blood flowing again to relieve those symptoms.”
‘Lie on your left side for better blood flow’
You may have heard this recommendation, and this is why: in pregnancy, your expanding uterus compresses the vessels that carry blood from your legs to your heart. Lying flat on your back can further impact this compression.
While researchers are still determining whether the “left lateral position” has an effect on the risk of stillbirth or other complications, we do know that it does affect blood flow between the mother and fetus.
Research has shown that fetal oxygen saturation levels can be 10% higher when the mother lies on her left side instead of on her back during labor. Another study showed that when you roll from your back to your side, your cardiac output will increase by about 20% if you’re around 26-30 weeks pregnant. At 32-34 weeks, it’s about 10% higher.
Side sleeping isn’t a hard-and-fast rule, and our recommendations can vary by patient. Generally, if you feel fine, you and your baby probably are fine. If you can choose a position for sleep, your left side is great because it also relieves pressure on your liver, kidneys, and back muscles. If you wake up on your back, don’t worry – just try to get back to sleep the best you can.
What happens after the baby is born?
After your baby is born, your body immediately begins to adapt to no longer being pregnant. All those measurements will get back to their typical levels within a few weeks after delivery.
If you had a lot of swelling or edema during your pregnancy, your blood pressure may go up after you deliver. This happens because all the fluid that accumulated in your tissues is released back into your bloodstream, and that sudden boost in volume increases the pressure in your blood vessels. Your provider may recommend a diuretic for a day or two to augment the diuresis.
Preeclampsia can develop after delivery, too, and this life-threatening postpartum complication can lead to a stroke, heart attack, or injury if you have a seizure. That’s why it’s so important to keep up with your postpartum care throughout your “fourth trimester.” Your provider will explain what your readings should be and how to check your blood pressure at home as well as signs and symptoms that would prompt you to seek evaluation.
Sometimes a pregnancy can reveal an underlying heart problem the patient wasn’t aware of. We also have a few patients whose hearts have trouble adapting to the demands of pregnancy. Serious conditions such as heart disease or postpartum cardiomyopathy (heart failure) may also emerge. If we suspect this kind of situation, we’ll connect you to our cardio-obstetrics specialists. This multidisciplinary team of maternal-fetal medicine doctors and cardiovascular specialists provide the best care possible for pregnant patients with heart conditions.
Related reading: 3 key topics to discuss at postpartum visits
When to see your provider
With all the new symptoms and side effects of pregnancy, it can be difficult to know when it’s worth a call to your doctor. We want to know if unusual symptoms start suddenly or last longer than normal:
- Frequent or prolonged nose bleeds
- Palpitations that don’t dissipate quickly
- Daytime swelling that doesn’t go away or gets worse overnight
- Coughing or wheezing when you’re lying down
- Fatigue that limits your normal activity
If you have sudden or intense chest pain or shortness of breath, head to the emergency department right away. When you check in, be sure to tell them you’re pregnant so the care team knows what to look for.
Every Ob/Gyn will tell you that being pregnant can cause unexpected body changes. But your body knows what to do. If you have any questions about heart health in pregnancy, give us a call – it’s what we’re here for.
Related reading:
Navigating pregnancy with a heart condition: What you need to know
Pregnancy can predict future heart health: Tips to shape your destiny
To talk with a pregnancy provider, schedule an appointment by calling 214-645-3838 or requesting an appointment online.
