Resting heart rate consistently rises throughout gestation. This cardiac change is a normal physiological adaptation, allowing the mother’s cardiovascular system to manage the unique demands of supporting a developing fetus. The increase optimizes blood flow and nutrient delivery.
Why Cardiac Output Must Increase
The primary driver for the heart rate increase is the necessary surge in cardiac output, the volume of blood the heart pumps each minute. This increase maintains adequate blood flow to the placenta and the mother’s organs. Total blood volume expands significantly, increasing by 30% to 50% above pre-pregnancy levels to accommodate new circulatory demands.
Cardiac output is calculated by multiplying Heart Rate by Stroke Volume. Early in pregnancy, the increase in output is driven more by stroke volume (the amount of blood pumped with each beat). As gestation progresses, however, the heart rate becomes the main factor sustaining the elevated cardiac output.
The systemic change is also a response to a drop in peripheral vascular resistance (PVR), which is the resistance to blood flow in the arteries. Hormones like progesterone cause blood vessels to relax and widen, lowering overall resistance. To compensate for this decrease and prevent blood pressure from dropping too low, the heart must pump faster. This increased heart rate maintains sufficient circulation, ensuring the uterus, kidneys, and skin receive necessary blood flow for fetal growth and maternal thermoregulation.
The Progression of Heart Rate Across Trimesters
The cardiovascular adaptation begins early, with the resting heart rate starting to increase around five to eight weeks of gestation. This initial change marks the beginning of the body’s commitment to increasing blood flow. The increase continues steadily throughout the pregnancy, though the magnitude of the change varies among individuals.
The typical increase is approximately 10 to 20 beats per minute (BPM) above the pre-pregnancy resting rate by the third trimester. The peak increase generally occurs in the late second or early third trimester. Once the heart rate reaches this peak, it stabilizes and remains elevated until delivery.
This consistent increase is a normal benchmark of healthy physiological adaptation. Following childbirth, the heart rate gradually returns to the pre-pregnancy baseline, a process that typically takes several weeks.
When Palpitations Require Medical Attention
Due to increased heart rate and blood volume, many people experience heart palpitations—sensations of the heart fluttering, pounding, or skipping a beat. These brief, occasional episodes are common and generally considered a harmless side effect of normal physiological changes. Hormonal shifts and the heart’s extra work contribute to the feeling of a more noticeable heartbeat.
While most palpitations are benign, certain associated symptoms require immediate contact with a healthcare provider. Lifestyle adjustments, such as ensuring adequate hydration and avoiding excessive caffeine, can help manage common palpitations. Urgent medical attention is necessary if symptoms are severe or persistent, or if they occur alongside other concerning signs.
Warning Signs
- Palpitations that are persistent or severe.
- Chest pain or discomfort.
- Lightheadedness, significant dizziness, or fainting (syncope).
- Sudden onset of shortness of breath, especially at rest.
- A rapid pulse or an irregular rhythm that lasts for a long period.