A person’s resting heart rate (RHR) is the number of times the heart beats per minute while the body is at rest. The normal RHR for a non-pregnant adult is typically between 60 and 100 beats per minute.
When a person becomes pregnant, the entire cardiovascular system undergoes a profound transformation. This systemic change includes an expected and entirely normal increase in the resting heart rate. The heart must work harder to manage the demands of gestation, which requires an adjustment in how frequently it pumps blood. These cardiovascular changes are a necessary adaptation to support the developing fetus and the maternal organs.
Expected Heart Rate Changes During Pregnancy
The body’s adjustment to pregnancy involves a measurable increase in RHR above the individual’s baseline. Most pregnant people can expect their resting heart rate to rise by approximately 10 to 20 beats per minute (bpm) throughout gestation. This elevation is a physiological response, not an indication of a problem.
The increase in heart rate does not happen all at once but progresses across the trimesters. The heart rate often begins to rise noticeably as early as five to eight weeks of gestation. This initial elevation often continues steadily as the pregnancy advances, moving from the first into the second trimester.
The heart rate typically reaches its peak during the third trimester, specifically around 32 to 34 weeks of gestation. For instance, a person who had a median RHR of 65 bpm before pregnancy might see their rate peak near 77 bpm in the late stages of pregnancy. This final increase helps the body manage the maximum demands of the growing uterus.
Studies show that the median heart rate at 12 weeks is around 82 bpm, and this can rise to a median of 91 bpm by 34 weeks. However, the normal range for a pregnant RHR is wide, with some healthy individuals exhibiting rates between 68 and 115 bpm in the third trimester. Therefore, healthcare providers focus on the change from the individual’s specific baseline rather than a single absolute number.
Physiological Reasons for Heart Rate Increase
The elevation in resting heart rate is directly linked to the dramatic changes in the circulatory system needed to sustain the pregnancy. One of the most significant changes is the expansion of the total blood volume, which increases by 30 to 50 percent. This substantial increase in circulating fluid volume requires the heart to pump a greater amount of blood per minute.
The volume of blood the heart pumps each minute is known as cardiac output, and this output increases by 30 to 50 percent during pregnancy. Initially, in the first trimester, the heart achieves this by increasing the amount of blood ejected with each beat, called the stroke volume. However, as the pregnancy progresses, the increased cardiac output is maintained primarily by the rise in the heart rate.
Hormonal shifts also play a direct role in regulating the heart’s function and rhythm. The increased levels of hormones like progesterone and estrogen affect the electrical signaling within the heart and the tone of blood vessels. These hormonal influences contribute to the heart’s need to beat faster to meet the body’s new circulatory demands.
The metabolic needs of the mother and the developing fetus require a constant and greater supply of oxygen and nutrients. The placenta, which connects the mother and the fetus, itself demands a significant blood flow. The faster heart rate is a mechanism to ensure that the increased blood volume is circulated rapidly enough to meet this heightened metabolic demand from the uterine-placental unit.
An additional factor is the decrease in systemic vascular resistance, which is the resistance to blood flow in the arteries. As the blood vessels widen, the blood pressure tends to drop, especially in the first two trimesters. The heart compensates for this lower resistance and reduced blood pressure by increasing its rate, ensuring adequate blood flow to all organs, including the uterus.
Recognizing Abnormal Heart Rhythms and Symptoms
While a faster heart rate is expected, it is important to distinguish between normal physiological changes and potentially concerning abnormalities. An unusually slow heart rate, known as bradycardia, or an excessively fast rate, known as tachycardia, may warrant medical investigation. For example, a resting heart rate that is persistently below 50 bpm or above 100 to 110 bpm should be brought to a provider’s attention.
Many pregnant people experience heart palpitations, which are brief sensations of the heart fluttering, pounding, or skipping a beat. These mild rhythm changes are common and often harmless, resulting from the combination of increased blood volume and hormonal fluctuations. They may be exacerbated by factors like dehydration, anxiety, or caffeine intake.
Certain symptoms, however, may indicate a more serious issue that requires immediate medical care.
Warning Signs
These concerning signs include:
- Severe shortness of breath that is not related to exertion.
- Chest pain or pressure.
- Persistent dizziness, lightheadedness, or fainting episodes.
A racing heart rate that feels sustained, or an irregular rhythm accompanied by these severe symptoms, should be reported to a healthcare provider right away. The focus of monitoring is to ensure the heart’s function remains efficient and that the mother and fetus are not placed under undue stress. Knowing the difference between the common, mild palpitations and these more serious warning signs is an important part of prenatal care.