Why pregnancy acts as a ‘physiologic stress test’ for a women’s heart

Pregnancy comes with many physiological and hormonal changes, as well as certain complications. One of the lesser-discussed aspects is how a woman’s heart is affected during those nine months, especially if she has a pre-existing cardiovascular condition. According to Dr Sameer Bhate, Senior Consultant & HOD, Adult Cardiac Surgery at Amrita Hospital, Faridabad, pregnancy acts as a powerful stressor on the cardiovascular system, even in otherwise healthy women.

“Pregnancy acts as a ‘physiologic stress test,’ as it increases cardiac workload by 30–50% to support the foetus,” Dr Bhate tells indianexpress.com. During this period, he further explains, a woman’s blood volume rises sharply—by nearly 40–50%—forcing the heart to pump significantly more blood every minute, and the heart rate increases by 10–20 beats per minute.

Moreover, the hormonal changes relax the vascular walls, while the expanding uterus restricts blood flow. “This can lead to increased pressure and, in some cases, varicose veins or clotting risks.”

For women with underlying medical conditions, this physiological load can become dangerous. “Women with heart valve disease already have compromised pumping mechanics or blood flow patterns. Pregnancy adds volume and output demand on top of that.” The extra blood volume can worsen valve leakage or obstruction, pushing the heart beyond its reserve.

“If a woman has a mechanical valve, she is at higher risk of blood clots during pregnancy. Besides, mechanical valves require anticoagulation, which may harm the fetus,” he further adds.

There is also an increased risk of hypertensive disorders, including pre-eclampsia and heart failure. “Chronic kidney disease similarly heightens risk, increasing the chances of pre-eclampsia, preterm birth, low birthweight and NICU admission.”

During pregnancy, heart rate increases by 10-20 beats per minute (image: pexels)

Protecting heart health during pregnancy, Dr Bhate stresses, must begin even before conception, with “honest risk assessment and counselling.” Once pregnant, careful and frequent monitoring becomes essential.

“Regular cardiology follow-up with clinical exams, ECG, and echocardiography to monitor ventricular and valve function, and management by a multidisciplinary pregnancy heart team can help detect worsening function, arrhythmias, or heart failure early.”  High-risk women may also require tailored delivery plans and specialist medication management.

Dr Bhate recalls a case of a 44-year-old Ethiopian woman, in whom pregnancy worsened a pre-existing heart condition. The cardiologist cites that the woman had undergone a bioprosthetic mitral valve replacement and, over the course of two decades, carried four full-term pregnancies.

“Each added sustained hemodynamic stress. Pregnancy accelerated the degeneration of her tissue valve, a known risk in younger women.” Over the years, she developed severe breathlessness and pulmonary hypertension.

“Evaluation showed the valve had worn out prematurely, necessitating a high-risk redo mitral valve replacement, complicated further by a single kidney.” Although bioprosthetic mitral valve degeneration is inevitable over time, in this case, “repeated pregnancies likely accelerated a process that is biologically expected.”

Dr Bhate says that timely surgery restored her cardiac function and stability, and that this example underlines the cruciality of frequent cardiovascular surveillance in pregnancy, especially in women with pre-existing heart conditions.

“Annual echocardiography after valve replacement, closer follow-up during and after each pregnancy, and early screening for rising pulmonary pressures would have helped detect valve degeneration sooner,” Dr Bhatte asserts, cautioning that frequent cardiovascular surveillance in pregnancy, especially in women with pre-existing heart conditions, is non-negotiable.

DISCLAIMER: This article is based on information from the public domain and/or the experts we spoke to. Always consult your health practitioner before starting any routine.