RHR is the number of times your heart beats per minute when your body is at rest. This measurement, often tracked by modern wearable technology, provides a view into your cardiovascular state. Pregnancy represents a period of profound physiological change as the body adapts to support the developing fetus. Understanding the normal RHR trend during this time offers valuable context for any observed fluctuations.
The Expected Rise in Resting Heart Rate During Pregnancy
The body undergoes significant cardiovascular remodeling to support the increased demands of the placenta and the growing fetus. This adaptation is the primary reason RHR is expected to rise throughout gestation. The total volume of blood circulating in the body can increase by up to 50% from pre-pregnancy levels.
To circulate this larger volume of blood, the heart must increase its output, which combines heart rate and stroke volume. Cardiac output typically rises by 30% to 50% during pregnancy. This increase begins early in the first trimester, with the RHR often rising by about seven to eight beats per minute by the tenth week.
The RHR continues its steady climb, generally peaking in the late second or early third trimester, around 32 to 36 weeks of gestation. By the end of pregnancy, the average RHR is typically elevated by 10 to 20 beats per minute. This represents a 20% to 25% increase over the pre-pregnancy baseline and is a normal sign that the cardiovascular system is managing its expanded workload.
Why Resting Heart Rate Appears to Drop
If your RHR shows a drop, it is often a relative change rather than a true decline below your original baseline. One common explanation relates to the normal physiological curve of pregnancy. The RHR increase may slow down, plateau, or slightly decrease toward the end of the third trimester, approximately seven weeks before delivery, after reaching its peak.
Another factor is your pre-pregnancy fitness level, which can mask the expected rise. Highly conditioned individuals, such as athletes, often have a naturally lower RHR, sometimes in the 40s or low 50s. For these individuals, the absolute RHR may only increase slightly or remain within a range that looks low compared to the general population.
A temporary drop may also be related to acute physiological improvements, such as excellent recovery. Improved hydration and high-quality sleep can lower the RHR because the body is less stressed and functions more efficiently. If a recent drop correlates with improved sleep or a reduction in daily stressors, it may reflect a positive temporary state.
Bradycardia and Warning Signs
While a slight or relative drop is usually not concerning, a true and sustained drop into an abnormally low range, known as bradycardia, requires medical evaluation. Bradycardia is generally defined as a heart rate below 60 beats per minute, though this threshold varies based on individual baseline and symptoms. This definition applies to the mother’s heart rate, not the fetal heart rate, which is monitored separately.
A significant RHR drop, especially if it falls below your established normal range, is concerning when accompanied by other physical symptoms. You should contact a healthcare provider immediately if a drop in RHR is paired with signs that may indicate poor blood flow.
Warning Symptoms
Warning signs include:
- Dizziness or lightheadedness.
- Fainting or near-fainting episodes.
- Shortness of breath disproportionate to activity.
- Chest pain.
- Extreme fatigue that is sudden or debilitating.
- A feeling of confusion.
These symptoms suggest the heart may not be effectively circulating oxygenated blood. A medical professional can determine if the change is a benign fluctuation or a sign of an underlying condition requiring intervention.
External Factors Affecting Heart Rate Readings
The technology used to track RHR, such as wearable devices, measures heart rate continuously, but the reported daily number is a calculation that can be easily skewed. Consistent measurement technique is paramount to establishing an accurate RHR trend. The most reliable reading is typically taken overnight during deep sleep or immediately upon waking, before you sit up, drink water, or consume caffeine.
Factors like recent consumption of caffeine or certain medications can temporarily raise your heart rate. A low reading taken after avoiding these substances might look like a drop when it is simply a cleaner measurement. Stress and anxiety levels also impact RHR, meaning a reading taken after a relaxing day may appear lower than one taken during a stressful period.
The accuracy of the device itself can also introduce variability. Wearable devices rely on optical sensors that can be affected by movement or a loose fit, leading to inaccurate data points. Looking at the long-term trend, rather than focusing on a single low daily number, provides a more accurate picture of your physiological changes throughout the pregnancy.