Elevated Heart Rate During Pregnancy

Pregnancy is a normal phenomenon. Still, your body's adjustments to pregnancy require major changes in your cardiovascular system. Cardiovascular adaptations serve a number of purposes, including to protect your normal physiologic functioning, to meet the increased metabolic demands of the pregnancy and to facilitate the growth and development of the fetus. In order for this to happen, your blood volume increases, as do your cardiac output and your heart rate.

Time Frames

A typical pregnancy lasts approximately 40 weeks, divided into three trimesters. The first trimester begins with conception and ends at the 15th week. The second trimester begins at 16 weeks and ends at week 27. The third trimester begins at 28 weeks and ends with the birth of the baby. Elevation of your heart rate is the natural result of a number of adaptive hemodynamic changes that occur over time, in each trimester of pregnancy.

First Trimester

In a normal, uncomplicated pregnancy, your resting heart rate will elevate by 15 to 20 beats per minute. As is the case with all of the major organ systems, cardiovascular changes that take place during pregnancy are believed to be triggered by hormonal signals, primarily increases in progesterone and estrogen, which alert the body to the presence of a fetus. These changes begin in the first trimester.

Second Timester

During the second trimester there is a generalized relaxation of smooth muscle along with dilation of the arteries. This change accommodates the increase in circulating blood volume while maintaining your normal blood pressure. This leads to a progressive elevation of your resting heart rate, which peaks in the second trimester. By the fourth month of pregnancy, cardiac output, or the quantity of blood your heart pumps, increases by 30 percent to 50 percent. This is the point in pregnancy when problems might present if you have any previously undiscovered heart irregularities.

Third Trimester

The period of maximum cardiac output occurs between week 28 and 35 of the third trimester. By the end of pregnancy, at about 40 weeks, your circulating blood volume will have increased to 40 percent to 90 percent above pre-pregnancy levels. The heart depends on an ample blood supply to ensure adequate delivery of oxygen and nutrients to both mother and baby. In the third trimester, these changes are critical to meet the increasing demands of a rapidly growing fetus and also for preparation for labor. During labor, the heart rate elevates during contractions and in response to pain.

Warning Signs

Normally, the healthy heart can withstand the cardiovascular changes that occur over the course of pregnancy. However, previously unknown heart problems might become apparent as the pregnancy progresses and the workload demands on the heart increase. Some common warning signs can include a racing or pounding pulse, shortness of breath even when at rest, lightheadedness, fainting spells, a persistent productive cough and palpitations, or skipped heartbeats.This is why it is so important to keep all scheduled prenatal appointments with your health care provider.