What is a normal resting heart rate (HR) during early second trimester pregnancy?

Normal Resting Heart Rate in Early Second Trimester Pregnancy

A normal resting heart rate during early second trimester pregnancy is typically between 80-95 beats per minute (bpm), representing an increase of 15-20 bpm above pre-pregnancy values. 1

Physiological Changes Affecting Heart Rate in Pregnancy

• Cardiac output rises 30-50% during pregnancy, resulting from increased stroke volume and a 15-20 bpm increase in maternal heart rate 1
• Heart rate progressively increases throughout pregnancy, with the median heart rate rising from 82 bpm at 12 weeks to approximately 91 bpm by 34 weeks 2
• This heart rate increase is a normal physiological adaptation to meet the increased metabolic demands of pregnancy 1
• Systemic vascular resistance decreases due to endogenous vasodilators (progesterone, estrogen, nitric oxide), leading to decreased mean arterial pressure that reaches its lowest point in the second trimester 1

Expected Heart Rate Patterns

• According to a large prospective cohort study, the normal range (3rd-97th percentile) for maternal heart rate during early second trimester is approximately 68-115 bpm 2
• The heart rate continues to rise progressively throughout pregnancy, reaching maximum values in the third trimester 2
• These changes begin in the first trimester and continue through the second trimester as part of normal cardiovascular adaptation 1

Clinical Implications

• A resting heart rate outside the normal range may warrant further investigation, especially if accompanied by other concerning symptoms 1
• Maternal early warning criteria consider a heart rate <50 or >130 bpm as abnormal and potentially requiring clinical attention 1
• Position changes can significantly affect heart rate and cardiac output during pregnancy - the left lateral position increases cardiac output compared to the supine position 1
• The supine position should be avoided after 20 weeks as it can cause inferior vena cava compression, reducing venous return and potentially causing hypotension 1

Other Vital Sign Changes in Early Second Trimester

• Blood pressure typically reaches its lowest point around 18-19 weeks of gestation before gradually rising again 2
• Respiratory rate remains relatively stable throughout pregnancy, with a median of 15 breaths per minute 2
• Oxygen saturation begins to decrease slightly from 12 weeks onward 2
• These changes represent normal physiological adaptations rather than pathological processes 1

Monitoring Considerations

• Regular monitoring of maternal vital signs, including heart rate, is important for detecting potential complications 1
• Significant deviations from the expected heart rate pattern may indicate underlying cardiovascular pathology 1
• When interpreting heart rate measurements, it's important to consider the patient's position, activity level, and other factors that might temporarily affect readings 1