Does Baby’s Heart Rate Reveal Their Sex?

We've all heard old stories passed down from one generation to another about how our families originally discovered the sex of a baby.

“You’re carrying low, so it must be a boy.”

"You don’t have morning sickness? It must be a girl.”

While these myths can be fun to toss around, there’s no science to back them up. And the same goes for the belief that baby’s heart rate predicts their sex. Obstetrician Justin Lappen, MD, explains the facts about fetal heart rate and why it doesn’t reveal the sex of your baby.

Do boys and girls have different heart rates?

You can often see and hear your baby’s heartbeat at your regular prenatal appointments. Using ultrasound, your obstetrician can measure the heart rate of your fetus as early as six to eight weeks into pregnancy.

An average fetal heart rate ranges from 110 to 160 beats per minute (bpm) and changes when the baby is active. Some babies have heart rates that are slower or faster than average. But this has nothing to do with the sex of your baby.

“The fetal heart rate does not predict the sex of the baby,” says Dr. Lappen. “Studies have found no difference between male and female fetal heart rates.”

Tests that reveal baby’s sex

While the baby’s heartbeat may not clue you in on boy vs. girl, you can find out with these tests:

Mid-pregnancy ultrasound

You can usually find out the big news during the second trimester ultrasound. It takes place around the 20th week of pregnancy and checks your baby’s growth and well-being.

“During this ultrasound, we are usually able to identify male and female genitalia,” says Dr. Lappen. “But before 16 weeks or so, an ultrasound isn’t a reliable way to determine the sex of the fetus.”

Prenatal cell-free DNA screening

A prenatal cell-free DNA screening uses a sample of the mother’s blood to look for DNA from the pregnancy. The results of this screening can reveal whether a baby has a higher risk of certain chromosomal disorders.

The results also show whether you’re having a boy or a girl. But doctors typically don’t use this test exclusively as an early sex reveal.

“Cell-free DNA tests are usually for women with a higher risk of having a baby with a chromosomal abnormality,” explains Dr. Lappen. “If a woman is interested in a cell-free DNA screening, she should talk with her obstetrician.”

Prenatal genetic tests

Prenatal genetic tests help doctors diagnose certain genetic disorders in a fetus. And these tests also reveal the baby’s sex. Prenatal genetic tests include:

• Chorionic villus sampling (CVS): Doctors usually perform CVS around 11 to 13 weeks of pregnancy. CVS takes a small sample of cells from the placenta. The placenta is an organ that grows with your baby, providing oxygen and nourishment.
• Amniocentesis: You can get an amniocentesis after 15 weeks of pregnancy. The test involves taking a sample of the amniotic fluid, the watery fluid that surrounds the baby.

These tests carry a small risk of miscarriage or infection, so they shouldn’t be your go-to for finding out your baby’s sex.

“Anyone can have an amniocentesis or CVS if they choose,” says Dr. Lappen. “But they’re not something we would use just to find out the baby’s sex. These tests are helpful for women who want to know if there are any problems with their pregnancy.”

Finding out your baby’s sex: Do what’s right for you

There is no “perfect time” to find out your baby’s sex. Some women find out early during a prenatal screening or test. Many get the news during their 20-week ultrasound. And others choose to wait until delivery day.

“There are safe and accurate ways to find out the sex of your baby,” Dr. Lappen says. “Talk to your obstetrician or midwife so you can make the decision that works best for you.”