Resting Heart Rate (RHR) is the number of times the heart beats per minute while the body is at complete rest. For most adults, the typical RHR range falls between 60 and 100 beats per minute (bpm). During pregnancy, the cardiovascular system undergoes significant adjustments that naturally cause the RHR to increase. This elevated heart rate reflects the body’s adaptation to support both the pregnant person and the developing fetus. Tracking this change is an important part of monitoring maternal health throughout gestation.
The Physiological Basis of Increased Heart Rate
The increase in heart rate is a direct consequence of the body’s effort to manage an expanded circulatory workload. The most significant change is the massive expansion of blood volume, which increases by 30 to 50 percent over the course of the pregnancy. This extra fluid volume is necessary to perfuse the placenta and supply the growing needs of the fetus, placing a substantial demand on the heart.
To move this larger volume of blood efficiently, the heart must dramatically increase its output, which is the total amount of blood pumped per minute. Cardiac output rises by 30 to 50 percent during pregnancy, achieved by a combination of a higher stroke volume and a faster heart rate. In later gestation, the rising heart rate becomes the primary mechanism for maintaining this elevated cardiac output.
Hormonal shifts also play a role in circulatory remodeling, particularly high levels of progesterone and estrogen. These hormones cause vasodilation, which is the widening of blood vessels, leading to a decrease in systemic vascular resistance. The heart compensates for this drop by beating more frequently to maintain adequate blood flow. These physiological changes begin as early as the first trimester and represent a healthy, expected adaptation.
Expected Resting Heart Rate Ranges During Pregnancy
The RHR typically begins its upward trend around 8 to 12 weeks of gestation, rising gradually and progressively. The total expected increase in RHR is usually between 10 to 20 beats per minute (bpm) above the individual’s non-pregnant baseline. This increase reaches its peak rate during the third trimester.
For example, studies tracking large groups show the average RHR is around 79 bpm at 10 weeks, rising to a peak average of approximately 87 to 91 bpm by 34 to 40 weeks. While these averages provide a guideline, individual variation is significant, and there is a wide range of normal RHRs during pregnancy.
At 34 weeks, the RHR may fall anywhere between 68 and 115 bpm and still be considered within the expected physiological range. The heart rate returns to its pre-pregnancy rate gradually after delivery, a process that can take several weeks.
Recognizing When Heart Rate Changes Warrant Medical Attention
While an elevated RHR is normal during pregnancy, certain heart rate changes or accompanying symptoms signal a need for medical consultation. Tachycardia, an abnormally fast heart rate, is a concern if the RHR is sustained significantly higher than the expected range. Although a sustained RHR over 100 bpm is a general marker for concern, a more specific threshold used in maternal early warning criteria is a heart rate greater than 130 bpm.
This rapid rate, or any persistent deviation from a person’s individual baseline, should be evaluated by a healthcare provider. Bradycardia, a very slow heart rate, can also be concerning, particularly if the RHR drops below 50 bpm. These heart rate changes are more worrisome when they occur alongside other symptoms that indicate possible complications.
Immediate medical attention is required for the following symptoms:
- Persistent palpitations that last longer than 30 seconds or are accompanied by chest pain.
- Unexplained and persistent shortness of breath, especially when not related to physical exertion.
- Fainting.
- Severe dizziness or lightheadedness.