When Does A Fetus Develop A Heartbeat?

You are going to have a baby! For many women, the first, tangible realization of this major milestone comes with an ultrasound. The image of the baby’s heart – visible as a tiny, pulsing speck on an ultrasound monitor – is immensely moving. But there’s much more going on than you’d ever imagine. The fetal heartbeat plays a crucial role in the health of your baby – during pregnancy, birth, and beyond. Fortunately, the technology used to monitor your baby’s heart offers vital information that can indicate the viability of a pregnancy and detect congenital heart abnormalities early on.

When Does A Fetus Develop A Heartbeat?

The baby’s heart – initially a tube-shaped structure that develops into the chambered organ we are familiar with – begins to form early on, in the days after fertilization.¹ Here’s a rough timeline:

• Week 3: Fetal heart begins to form at day 22 after fertilization, but it is too soft to be heard.
• Week 5: Fetal heart chambers start to develop.
• Week 6: Heart rate increases to 100–160 beats per minute (bpm). This is when you can see the baby’s heart beating during prenatal ultrasound monitoring.
• Week 8: Baby’s heartbeat has a steady rhythm.²
• Week 10: Heart rate increases to about 170 bpm and stabilizes at about 130 bpm close to the time of birth.³

What powers the baby’s heart to begin beating? What controls the speed of the first tiny flutters? According to scientists, the answers to these mysteries could hold the clues to our understanding of congenital heart defects and their treatments.⁴

What Is A “Normal” Heart Beat For A Fetus?

Medical opinion varies considerably about what constitutes a “normal” heart rate for a baby in the womb, but it is generally accepted that it should range from around 110 to 150 bpm or 120 to 160 bpm.⁵ As your baby moves around in your uterus, there will be variations in the heart rate. That’s quite normal. Babies have been known to have a lower heart rate of 90 bpm and still grow normally. During prenatal check-ups, your doctor will also monitor the baby’s heart rhythm. If an irregular rhythm is detected, don’t worry! This is common because of the still immature electrical system of the heart. At times, during an ultrasound, the heartbeat may drop for a few seconds – again, these are all perfectly normal variants and not a cause for anxiety!⁶

If the arrhythmia persists, however, your doctor will turn to echocardiography to take a sonogram of the heart, assess the condition, and plan out a course of treatment.⁷

Devices To Monitor Fetal Heartbeat

Monitoring the fetal heart involves measuring its heart rate and rhythm. This helps doctors check on a baby’s development. Here’s a quick look at devices used in modern medical practice:

• A fetal Doppler, using an ultrasound probe that is moved over the mother’s belly, bounces sound waves off internal organs. The rebounding echoes are translated by a computer into patterns that are visible on a screen. However, this device does not display images.
• During the sixth week of pregnancy, your OB/GYN may use a transvaginal ultrasound to check on the baby’s heartbeat. In this method, a probe is gently inserted into the mother’s vagina. The sound waves echoing off the uterus are converted into images that display the fetal heart beating and provide readings of the number of beats per minute. This method helps the doctor determine the progress of the pregnancy.
• At times, external methods don’t yield accurate readings. In such instances, the doctor may resort to another method of internal monitoring, just prior to birth. This may be undertaken after the mother’s amniotic sac breaks open and releases its fluid. A fine wire or electrode connected to a monitor is inserted through the mother’s open cervix and attached to the baby’s head. The internal method makes it possible to monitor both the baby’s heart rate and the mother’s uterine contractions and compare the two.⁸

Is Fetal Heart Monitoring A Must?

Fetal heart monitoring is now a part of routine check-ups. In high-risk pregnancies, heart monitoring becomes even more important. Some situations where monitoring plays a crucial role are:

• If a mother is diabetic or has high blood pressure.
• If the baby’s growth rate is slower than desirable.⁹
• If medications given to prevent early labor may have impacted the baby.¹⁰

Tracking Abnormalities

For a new parent, a baby born with a heart defect is a traumatizing experience, fraught with anxiety and fear. This is one area where medical technology can help save precious lives. Tracking the heartbeat helps doctors detect any structural abnormalities in the fetal heart early on. They are able to better manage the course of the pregnancy and plan delivery and further treatment for the baby.¹¹

Timing is also an important factor here. Fetal heart monitoring can help doctors determine if treatment for a baby’s heart defect can be delayed until after birth or if it requires intervention soon after delivery.

A heart rate that is above normal (known as tachycardia) and below normal (bradycardia) could be a cause for concern.¹² A below normal heart rate in the first trimester could indicate that the pregnancy may not reach full term.¹³ There’s also a possibility that an excessively high or low heart rate in early pregnancy could be linked to different types of abnormal chromosomes in the baby.¹⁴

How Can You Help Your Baby’s Heart Development?

While genetics play a large part in the development of a baby’s heart, there’s plenty you can do to help keep you and your baby healthy, like eating fresh, wholesome food, getting enough sleep, and managing your stress levels. Here are a few other things to keep in mind:

• Take folic acid supplements before and during your pregnancy to help prevent the development of congenital heart disease¹⁵
• Aerobic exercise during pregnancy influences fetal heart rate. Using ultrasound technology, researchers have concluded that moderate and regular exercise through pregnancy leads to a lowered fetal heart rate and increased heart rate variability (a measure to assess the control of the heart by the nervous system), both of which are considered beneficial to the baby. ¹⁶ Another study suggests that exercise during pregnancy may benefit the baby’s heart and nervous system up to a few weeks after delivery. More research is required to determine if the effects of maternal exercise go beyond a month after birth or if it offers protection from later heart disease.¹⁷ Bottom line: Exercise is good for you and your baby, and safe too – just don’t overdo it!¹⁸
• Ayurveda offers advice on specific foods to be consumed during every month of pregnancy, correlated to the baby’s development. Ancient ayurvedic texts also list a vast range of cereals, pulses, “fruit vegetables” (pumpkins, kidney beans, peas, and tomatoes), root vegetables and tubers, milk and milk products, meats, herbs, and aromatic spices to promote the health and strength of both mother and baby.¹⁹
• Are you a smoker? Then it’s time to quit – now! There’s a mountain of evidence proving that smoking just before pregnancy or during the first trimester could lead to heart defects in the baby.²⁰
• Diabetic moms run the risk of having babies with congenital heart disease. If you are diabetic, carefully follow your doctor’s advice on how to control your blood sugar.²¹

Fun Fetal Facts

• The various periods of growth and development of a baby during its first eight weeks of life is referred to as the “Carnegie Stages.” In all, there are 23 Carnegie Stages.²²
• During the first eight weeks, the baby is referred to as an embryo (“growing within”). From eight weeks to the time of birth, the baby is a fetus or “unborn offspring.”²³
• A baby’s heart beats 54 million times from the time it is formed to the moment of birth.²⁴
• At 6–8 weeks, the fetal heart has grown into four chambers. Its development is nearly complete and it beats rapidly at about 167 bpm.²⁵