Baby marathon: How pregnancy pushes your heart to its limits

Published on 23 October 2025

Pregnancy makes your heart work 50 per cent harder. Here’s what happens inside your body, when to seek help and how to protect your heart.

During pregnancy, a woman’s heart pumps up to 50 per cent more blood to support the growing baby. This makes pregnancy one of the most demanding periods for the cardiovascular system.

Most women adapt well to these changes. But for some, pregnancy can uncover previously undiagnosed heart conditions or increase the risk of complications during and after childbirth.

“Pregnancy triggers dynamic changes in the cardiovascular system to meet the increasing demands of the developing foetus and to prepare for labour and breastfeeding,” said Dr Lim Yoke Ching, Senior Consultant, Department of Cardiology, National University Heart Centre, Singapore (NUHCS).

Cardiac output, or the volume of blood pumped per minute, rises rapidly in the first trimester. By mid-pregnancy, heart rate is about 25 per cent higher than normal, and hormones such as progesterone and oestrogen relax blood vessels to accommodate the surge in blood flow.

“These adaptations ensure adequate circulation to vital organs such as the uterus, kidneys and liver,” Dr Lim explained. “Blood pressure tends to fall slightly in early pregnancy before increasing again towards the third trimester.”

The result is a cardiovascular system operating close to its limits for months – what Dr Lim described as “the body’s natural stress test for the heart”.

When common symptoms could mean something more

Shortness of breath and mild palpitations are common as pregnancy progresses. But cardiologists caution that some symptoms should raise red flags.

“Most pregnant women report feeling more breathless as the pregnancy progresses,” said Dr Lim. “This is mainly due to the growing uterus pressing against the diaphragm and lungs, increasing oxygen demand for both the pregnant woman and the baby, as well as changes in progesterone levels.”

However, she warned that sudden or worsening breathlessness, especially at rest or with light activity, is not normal and should be checked immediately.

Other danger signs include persistent leg swelling, or chest discomfort accompanied by sweating, dizziness or a racing heartbeat.

The pregnancy complications that strain the heart

Two conditions can put pressure on the heart: gestational hypertension and pre-eclampsia.

“Gestational hypertension refers to new-onset hypertension in a pregnant woman after 20 weeks of gestation,” said Dr Lim. “Pre-eclampsia is characterised by gestational hypertension with other organ involvement, including protein in the urine, abnormal liver enzyme tests, severe headache, visual disturbances, fluid retention and abdominal pain.”

If untreated, pre-eclampsia can lead to seizures, premature birth or even heart failure. While these conditions usually resolve after delivery, research shows that they can have long-term consequences.

“Women with a history of gestational hypertension and pre-eclampsia are at increased risk of developing hypertension at a younger age of approximately 40 to 50 years old,” said Dr Lim. “They are also at increased lifelong risk of cardiovascular events such as heart attack, heart failure and stroke.”

Those who develop heart failure during pregnancy often need medication and careful follow-up. “With advances in medicine, about 50 per cent of these women will have complete recovery of heart function within six months,” Dr Lim said. “However, some remain symptomatic despite optimal therapy, and about one-third may develop heart failure again in a later pregnancy.”

Why pregnancy heart health matters

Doctors are paying closer attention to heart function during pregnancy as evidence grows that complications like pre-eclampsia can predict future cardiovascular risk.

“Pregnancy can unmask underlying heart conditions,” said Dr Lim. “It is a critical window for early detection and prevention of cardiovascular disease in women.”

That makes regular check-ups and early reporting of symptoms essential. “A thorough history-taking and physical examination is necessary in every pregnant woman reporting symptoms,” she said. “At times, further investigations such as an electrocardiogram or an ultrasound of the heart are required.”

After childbirth, the watchfulness should not stop. New or worsening symptoms such as chest pain, breathlessness or swelling should be reviewed promptly.

Women with existing heart conditions should also seek medical advice before conception, as certain medications may need adjustment.

The takeaway for mothers-to-be

Pregnancy is a physiological triumph, but also a reminder of how finely tuned the human heart is. Experts say that awareness, regular monitoring and timely intervention can make the difference between a healthy pregnancy and a dangerous one.

As Dr Lim shared, “It is never wrong to seek medical attention for symptoms, even though family and friends may say they are normal.”

In consultation with Dr Lim Yoke Ching, Senior Consultant, Department of Cardiology, NUHCS.