A pregnant person’s resting heart rate climbs steadily throughout most of pregnancy, typically rising by 10 to 20 beats per minute above their pre-pregnancy baseline. This increase is a normal part of the body’s effort to push roughly 50 percent more blood volume through the circulation to support the placenta and growing baby. But because that same symptom, a fast or pounding pulse, can also signal something genuinely wrong, knowing the difference matters more during pregnancy than almost any other time in life.
Why Your Heart Rate Rises During Pregnancy
From early in the first trimester, the cardiovascular system begins remodeling itself. Blood volume expands, the heart pumps more blood with each beat (a higher stroke volume), and the blood vessels relax and widen, dropping overall vascular resistance. The combined result is a higher cardiac output, the total amount of blood your heart moves per minute, driven by increases in both stroke volume and heart rate.1Physiologia. Cardiovascular and Respiratory Adaptations During Pregnancy and Exercise in Pregnancy These changes are progressive: plasma volume, heart rate, stroke volume, and cardiac output all keep climbing as the pregnancy advances.2PubMed Central. Pulmonary hypertension in pregnancy: hemodynamic challenges, maternal risk, and multidisciplinary management
The rising resting heart rate is not constant throughout, though. Wearable-device data from active pregnant women shows a gradual, steady increase in daily resting heart rate across most of pregnancy, but around seven weeks before the due date the trend reverses: resting heart rate begins to drop and continues declining into the postpartum period.3PubMed Central. Monitoring one heart to help two: heart rate variability and resting heart rate using wearable technology in active women across the perinatal period So if you notice your smartwatch showing a slightly lower resting heart rate in the last month or two before delivery, that pattern has been documented and is not in itself a reason to worry.
What Counts as a Normal Range
Outside of pregnancy, a typical adult resting heart rate sits between about 60 and 100 beats per minute. During pregnancy, the upper end of that range shifts upward. One study of pregnant women found an average ECG heart rate of about 100 beats per minute, with blood pressure running on the lower side, around 110/71.4Indian Journal of Cardiovascular Disease in Women. Electrocardiographic Changes during Normal Pregnancy That means a pregnant person sitting comfortably in the high 80s or low 90s is well within the expected window, and even readings just above 100 may be perfectly physiological depending on the individual and the stage of pregnancy.
The tricky part is that “normal” is relative to your own baseline. Someone whose pre-pregnancy resting heart rate was 55 might find 80 alarming, while someone who usually runs at 75 might barely notice a rise to 90. Tracking your own trend over weeks gives you more useful information than comparing a single reading to a population average.
Palpitations and Skipped Beats
Feeling your heart flutter, skip, or pound is remarkably common during pregnancy, and in most cases it reflects benign extra beats rather than a dangerous rhythm. Holter monitoring studies comparing pregnant women who reported palpitations and dizziness to controls found that both groups had high rates of extra heartbeats: atrial premature beats appeared in over half of participants in both groups, and isolated ventricular premature beats showed up in roughly 50 to 60 percent.5PubMed. Incidence of arrhythmias in normal pregnancy and relation to palpitations, dizziness, and syncope Pregnant women with palpitation symptoms did tend to have more frequent and more varied ventricular extra beats, but the key finding is that extra beats themselves are extremely common in normal pregnancy even when you feel nothing at all.
The hormonal, autonomic, and hemodynamic shifts of pregnancy collectively increase susceptibility to these rhythm glitches.6PubMed Central. Management of Arrhythmias During Pregnancy in Africa Higher circulating blood volume stretches the heart chambers slightly, estrogen and progesterone alter electrical conduction, and the autonomic nervous system tilts toward a more activated state. All of this can trigger occasional extra beats or brief runs of fast rhythm without any underlying heart disease being present.
Position Matters More Than You Might Think
By the second half of pregnancy, lying flat on your back can cause a noticeable increase in heart rate. The reason is mechanical: the weight of the uterus compresses the large vein returning blood from the lower body, reducing the amount of blood reaching the heart. In response, the heart speeds up to try to maintain adequate blood flow. Studies confirm that this heart rate jump is a real compensatory response; women lying on their backs showed faster heart rates than when they were in the left-side-down position, even as blood flow through the compressed vein dropped.7PubMed. Hemodynamic changes in women with symptoms of supine hypotensive syndrome
Some women also feel lightheaded, dizzy, or nauseated when lying flat, a constellation called supine hypotensive syndrome. If you notice your heart racing or feel faint when you roll onto your back, shifting to your left side usually resolves it quickly. The left-side position takes pressure off the vena cava and lets blood flow return to normal. This is also why many prenatal care providers suggest left-side sleeping in later pregnancy, though the occasional moment on your back is not dangerous for most people.
When a Fast Heart Rate Becomes a Red Flag
The fact that some heart rate increase is expected during pregnancy can make it harder to spot a rate that is too high. Persistent tachycardia, a resting heart rate staying above 100 beats per minute outside the context of physical effort, position changes, or anxiety, always deserves clinical attention.8PubMed Central. Tachycardia in pregnancy: when to worry? Common non-cardiac causes include anemia, thyroid problems, infection, dehydration, and medication effects. All of these are treatable, and some, like iron-deficiency anemia, are especially common during pregnancy.
Certain accompanying symptoms turn palpitations from a nuisance into an urgent concern. Fainting, pre-existing structural heart disease, chest pain, or significant breathlessness alongside a racing heart are considered red flags that warrant prompt investigation and referral to a cardiologist.9PubMed Central. Managing palpitations and arrhythmias during pregnancy If you have a known heart condition and become pregnant, the risk of arrhythmias can be amplified by the added hemodynamic stress, so close monitoring from early pregnancy onward is standard practice.
Supraventricular Tachycardia During Pregnancy
Supraventricular tachycardia, or SVT, is a specific type of fast rhythm originating above the ventricles that can push the heart rate above 120 beats per minute and sometimes well beyond. Pregnancy’s increased cardiac output and elevated baseline heart rate can set the stage for SVT even in women with no prior history of it.10PubMed Central. Supraventricular Tachycardia in Pregnancy: Gestational and Labor Differences in Treatment SVT episodes may be triggered by mechanical stretch of the heart, hormonal shifts, or simply the heightened excitability of the electrical system during pregnancy.11PubMed. Palpitations: what is the mechanism, and when should we treat them?
Most uncomplicated SVT episodes during pregnancy end well for both mother and baby, but the episodes can lead to emergency interventions, including emergency cesarean section if the rhythm persists or causes hemodynamic instability, which raises surgical and preterm delivery risks.12British Journal of Anaesthesia. Supraventricular tachycardia in pregnancy: a case series and management For people who experience recurrent SVT during pregnancy, treatment options include vagal maneuvers as a first step, certain antiarrhythmic medications considered safer in pregnancy, and in rare cases electrical cardioversion, which has been performed safely during pregnancy when necessary.
Peripartum Cardiomyopathy and the Tachycardia Signal
One of the more serious conditions linked to persistent tachycardia in late pregnancy or the early postpartum period is peripartum cardiomyopathy (PPCM), a form of heart failure that weakens the heart muscle around the time of delivery. In this condition, the heart’s pumping ability drops, and the body compensates in part by speeding up the heart rate. About 60 percent of women diagnosed with PPCM had resting heart rates above 100 at the time of diagnosis.13PubMed Central. Heart rate as an early predictor of severe cardiomyopathy and increased mortality in peripartum cardiomyopathy
The degree of tachycardia at diagnosis appears to be a meaningful prognostic indicator. Women whose heart rate was 120 or higher when PPCM was identified were roughly four times more likely to experience major adverse events, including death, heart transplant, or need for a mechanical heart-assist device, compared to women whose heart rate was below 100.14PubMed. The association of heart rate with adverse outcomes and recurrent heart failure hospitalization in peripartum cardiomyopathy The practical takeaway: unexplained resting tachycardia in the weeks before or after delivery, especially paired with new shortness of breath, swelling, or fatigue beyond what feels normal, should be evaluated promptly. PPCM is uncommon but treatable, and outcomes are better when it is caught early.
Tachycardia and Blood Clots During Pregnancy
Pregnancy increases the risk of venous blood clots, and pulmonary embolism, a clot that travels to the lungs, remains one of the leading causes of maternal death in high-income countries. A racing heart is the most common physical exam finding when a pulmonary embolism is present.15Journal of Urgent Care Medicine. Shortness of Breath in Pregnancy: Differentiating Physiology from Pathology in Urgent Care The challenge is that mild shortness of breath and a slightly elevated heart rate are also perfectly normal in pregnancy, so clinicians need to look at the full picture: sudden onset, leg swelling on one side, chest pain with breathing, and low oxygen levels all raise suspicion for a clot. If you experience sudden worsening of breathlessness paired with a rapid pulse, especially after a period of immobility or travel, it is worth getting evaluated the same day.
What About a Heart Rate That Seems Too Low
While most pregnancy conversations focus on a fast pulse, an unusually low maternal heart rate can also carry information. Research has found that pregnancies with lower maternal heart rates were associated with lower birthweight babies, and the likely explanation is that a low heart rate may signal that the cardiovascular system did not adapt as robustly as expected. Poor placental development can lead to inadequate blood volume expansion, which in turn means the heart does not need to speed up as much, resulting in a lower-than-expected heart rate alongside reduced cardiac output.16PubMed Central. Effects of low maternal heart rate on fetal growth and birthweight
This does not mean every person with a naturally low resting heart rate should be alarmed. Endurance athletes and others with high cardiovascular fitness routinely have resting rates in the 50s or lower. The concern is more relevant when a low heart rate appears alongside evidence of poor fetal growth on ultrasound, because together these findings may reflect a problem with placental function.
Preeclampsia and Heart Rate Patterns
The relationship between heart rate and preeclampsia, the dangerous hypertensive condition of pregnancy, runs in a somewhat counterintuitive direction. You might expect high blood pressure to come with a racing heart, but in delayed postpartum preeclampsia, the opposite has been observed: affected women had an average heart rate of about 58 beats per minute, compared to roughly 83 in controls. Only 17 percent of women with delayed-onset postpartum preeclampsia had a pulse above 70, versus 83 percent of the control group.17PubMed Central. Changes in maternal heart rate in delayed post-partum preeclampsia The likely explanation involves baroreceptors, the body’s blood-pressure sensors, which detect the high pressure and reflexively slow the heart to try to compensate.
Earlier research on heart rate variability during pregnancy found that preeclampsia was associated with longer intervals between heartbeats during daytime, though the changes were subtle enough that heart rate variability alone was not a reliable way to separate preeclamptic pregnancies from normal ones.18PubMed. Preeclampsia and maternal heart rate variability Still, a notably slow pulse in the postpartum period, especially paired with headache, visual changes, or elevated blood pressure, is something worth mentioning to your care team.
Twin Pregnancies Push the Heart Harder
Carrying multiples amplifies every cardiovascular change of pregnancy. Women with twin pregnancies have been found to have resting heart rates averaging around 91 beats per minute, compared to about 81 in singleton pregnancies, a full 10-beat-per-minute gap.19PubMed. Cardioautonomic control in healthy singleton and twin pregnancies The autonomic nervous system shifts more dramatically in twin pregnancies, with greater sympathetic activation and less parasympathetic tone contributing to the higher rate.
Echocardiographic studies have confirmed that cardiac output is higher in twin than in singleton pregnancy, and that the heart achieves this not only through a faster rate but also through increased contractility, essentially squeezing harder with each beat.20PubMed. Maternal cardiovascular adaptations to twin pregnancy The practical implication is that cardiovascular reserve is more limited in a twin pregnancy. A heart rate that would be unremarkable in a singleton pregnancy might sit closer to the edge of what the heart can comfortably sustain with twins, which is part of why twin pregnancies are monitored more closely.
Exercise and Heart Rate During Pregnancy
Exercise naturally raises heart rate, and pregnant people sometimes worry about how high is too high. The old guideline of keeping the heart rate below 140 during exercise has been retired, because research has shown that moderate to even vigorous exercise is safe for most healthy pregnancies. A recent study of acute high-intensity resistance exercise found that maternal heart rate peaked at about 137 during squats and 131 during deadlifts. Importantly, fetal heart rate did not change after any of these exercises, and no fetal bradycardia was observed.21British Journal of Sports Medicine. Maternal and fetal responses to acute high-intensity resistance exercise during pregnancy
That said, the heart rate response to a given exercise intensity may feel different during pregnancy because of the already-elevated baseline. An activity that brought your heart rate to 130 before pregnancy might push it to 145 or higher for the same perceived effort. Current guidance generally focuses on exertion level (the “talk test,” where you can still carry on a conversation) rather than a specific heart rate ceiling, since individual variation is wide.
Your Heart Rate During Labor
Labor itself creates dramatic heart rate swings that can look alarming on a monitor if you are not expecting them. During the first stage of labor, maternal heart rate often dips during contractions, dropping by about 10 beats per minute on average, in a pattern that resembles the “early decelerations” more commonly associated with fetal monitoring. More than half of women in one study showed this pattern in at least half of their first-stage contractions.22PubMed. Maternal heart rate patterns in the first and second stages of labor
The second stage flips the script. During active pushing, maternal heart rate accelerates sharply, jumping an average of about 35 beats per minute and sometimes spiking above 140. Every woman in the study showed these accelerations during every pushing effort, and one in five peaked above 140. These swings are the body’s normal response to the extraordinary physical exertion of pushing, and they resolve once the contraction ends. The relevance for monitoring is that maternal heart rate artifacts can sometimes be picked up by fetal monitors, potentially being mistaken for the baby’s heart rate. Modern fetal monitoring systems account for this, but it is worth knowing that your own heart rate during pushing can be genuinely dramatic without anything being wrong.
How Clinicians Evaluate Pregnancy Heart Rate Concerns
When heart rate concerns come up during pregnancy, the diagnostic toolkit looks a bit different than it would otherwise. Echocardiography, which uses ultrasound to image the heart in real time, is the go-to investigation because it carries no known risks to the pregnancy. No adverse effects from diagnostic ultrasound of the heart have been identified, and agitated saline contrast is generally considered safe during pregnancy. Even transesophageal echocardiography, where a probe is guided into the esophagus for a closer view of the heart, can be performed in pregnant patients when needed, though the main concern in that case is the sedation required.23PubMed Central. Echocardiography for the Pregnant Heart
For rhythm concerns, Holter monitors and event recorders are used just as they would be outside pregnancy. Basic blood work to check for anemia, thyroid dysfunction, and infection is usually part of the workup when persistent tachycardia is found. ECGs in pregnancy can look slightly different from the non-pregnant state, with modest changes in electrical intervals, but standard intervals like the PR and QRS durations typically stay within normal limits.4Indian Journal of Cardiovascular Disease in Women. Electrocardiographic Changes during Normal Pregnancy One ECG parameter that does tend to drift toward the upper end of normal during pregnancy is the QTc interval, a measure of how long the heart takes to reset its electrical charge between beats. It stayed technically within range in about two-thirds of pregnant women in one study, but it sat higher than you would typically see in non-pregnant adults. Clinicians interpreting a pregnant patient’s ECG factor this in rather than treating it as abnormal.
Wearables, Home Monitoring, and What They Can and Cannot Tell You
Smartwatches and fitness trackers have made resting heart rate data more accessible than ever, and many pregnant people now notice their heart rate trends shifting weeks before any clinical measurement picks it up. The wearable-device study that documented the late-pregnancy drop in resting heart rate showed that consumer-grade optical sensors can track meaningful physiological patterns across pregnancy.3PubMed Central. Monitoring one heart to help two: heart rate variability and resting heart rate using wearable technology in active women across the perinatal period Heart rate variability, which many devices also report, followed a mirror-image trajectory: it declined gradually throughout most of pregnancy and then began recovering in the weeks before delivery.
The limitation is that wearables measure optical pulse, not an ECG, and they can be thrown off by motion, poor fit, and skin pigmentation. They are excellent for spotting trends over days and weeks but poor at diagnosing a specific rhythm. If your watch alerts you to a high or irregular heart rate, treat it as a reason to check in with your provider rather than a diagnosis in itself. A single elevated reading during a moment of activity or stress means very little. A persistent upward trend in your resting readings, especially after mid-pregnancy when the trajectory should be flattening or starting to decline, is more informative and worth discussing at your next visit.