An embryo does not have a heart, so what is a fetal heartbeat?


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Protesters demonstrate in Austin, Texas. Sergio Flores for The Washington Post via Getty Images
  • A new Texas law that effectively bans abortion after 6 weeks has also been dubbed the “heartbeat bill.”
  • At 6 weeks, an embryo does not have a fully formed heart. Rather, it has a group of cells (which eventually form a heart) that emit electrical signals, which can be detected by ultrasound.
  • The “sound” of heartbeats during an ultrasound is actually generated by the ultrasound machine itself during this time.

Texas recently passed Senate Bill 8, a law that bans abortion at 6 weeks gestation.

Also dubbed “the heartbeat bill,” the law – which came into force on September 1 – prohibits abortion on the first detection of a fetal heartbeat, which occurs around 6 weeks of pregnancy.

But reproductive health experts say that at 6 weeks an embryo doesn’t have a fully formed heart, but rather a cluster of cells that emit electrical signals.

These cells will eventually form a heart about 8 weeks after the last menstrual cycle.

It is only between 16 and 18 weeks of gestation that the heart, valves and vessels can be seen on ultrasound.

According to Dr. Jennifer Kerns, associate professor in the department of obstetrics, gynecology, and reproductive sciences at the University of California, San Francisco, the term “fetal heartbeat” does not accurately represent what is detected at 6 weeks pregnant.

“The term ‘heartbeat’ is very misleading for a 6 week old embryo. What’s called a ‘heartbeat’ is actually the electrical activity that can be seen on ultrasound,” Kerns told Healthline.

Up to 8 weeks of gestation, the pregnancy is still in the embryonic state. After 8 weeks, it’s called a fetus, Kerns explained.

Between 6 and 8 weeks, cells in the embryo change into specific cells that support a specific body system, such as the cardiovascular system or the pulmonary system.

But at 6 weeks, an embryo doesn’t have what we think of as a heart, Kerns said.

“A heart has four chambers with valves that allow blood to pool and then be pumped out to the body. At 6 weeks there is a cluster of cells that have electrical activity,” Kerns said.

Kerns said the term “fetal heartbeat” is misleading for a 6-week-old embryo since the “heartbeat” is technically electrical activity that can be detected by ultrasound.

“The sound produced from this electrical activity is generated by the ultrasound machine translating this electrical activity, not by the opening and closing of the valves, as is the case with a fully formed and functioning heart,” said Kerns said.

Dr. Nancy L. Stanwood, section chief of family planning at Yale Medicine and associate professor of obstetrics, gynecology and reproductive sciences at Yale School of Medicine, said it was important to clarify from first the moment of pregnancy.

Obstetricians and gynecologists start counting from the last menstrual period.

“That means for the first 2 weeks the person isn’t even pregnant yet,” Stanwood said.

In people with regular menstrual cycles, ovulation occurs 2 weeks after their period. Conception occurs in the fallopian tube around this time.

At around 3 weeks, the fertilized egg travels from the fallopian tube to the uterus, where the egg implants itself in the lining of the uterus, Stanwood explained.

It then takes about a week for the pregnancy hormone to be detected in a urine pregnancy test.

An embryo becomes a fetus 9 weeks after the last menstrual cycle, which is when the major structures of the heart are formed, Stanwood said.

The heart’s four chambers, valves and vessels can be seen in the second trimester, around 16 to 18 weeks, according to Kerns.

Ultrasounds are usually done at this stage to identify any cardiovascular dysfunction.

Even at this stage, the heart depends on other organ systems to function fully, Kerns said.

At 6 weeks, an embryo does not have a fully formed heart. Rather, it has a group of cells (which eventually form a heart) that emit electrical signals, which can be detected by ultrasound.

Reproductive health experts say the term “fetal heartbeat” is misleading.

It is only between 16 and 18 weeks of pregnancy that the heart, valves and vessels can be clearly seen during an ultrasound.

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