Since the moment you first got the good pregnancy news, you've maybe wondered whether you're having a boy or a girl — and jumped at a potential chance to learn the answer. Viral methods like the heart rate gender theory promise to reveal the answer using a simple early pregnancy data point, like fetal heart rate.
"Just wondering how accurate the heart rate theory is for gender prediction — and at what week does it start to be accurate?" asks What to Expect Community mom LauranS1111. "I work with five other girls who are all pregnant … They've been saying the heart rate theory starts when baby is over 12 weeks."
The truth, though, is a little more complicated. Here's what you should know about fetal heart rate, including whether it can indicate a boy or a girl.
- The heart rate gender theory says that a fetal heart rate under 140 beats per minute indicates you're having a boy and a faster heart rate points to a girl.
- There is no evidence to support the heart rate gender theory; like any other old wives' tale for finding out the sex, it has a 50% of being right due to chance.
- A better way to learn you're having a boy or girl is through noninvasive prenatal testing (NIPT), amniocentesis, chorionic villus sampling (CVS) or an anatomy scan.
What is the theory about fetal heart rate and gender?
The heart rate gender theory suggests that if the baby's heart rate is under 140 beats per minute, you're having a boy. If it's over 140 beats per minute, you're having a girl.
It's not exactly clear where the theory originated, but because grown men's and women's heart rates can differ — women have a higher resting heart rate than men, on average[1] — some researchers have theorized the heart rates of male and female fetuses may look different too.[2]
What exactly is fetal heart rate, and how is it measured?
Fetal heart rate is a measurement of how fast a fetus's heart is beating in utero. According to some research, a healthy rhythm increases from 110 beats per minute at week 5 to 170 beats per minute at week 9, then gradually settles to about 150 beats per minute by week 13.
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Most commonly, cardiac activity is detected around weeks 8 to 10 with a Doppler ultrasound device, says Christine Feigal, M.D., board-certified OB/GYN and vice chair of the OB/GYN department at MemorialCare Long Beach Medical Center in Long Beach, California.
So, can fetal heart rate indicate your baby's gender?
Unfortunately, fetal heart rate can't predict whether your baby will be a boy or a girl. Research comparing male and female fetal heart rates has found that there's no statistically significant difference between the two.[3]
"There's no evidence that fetal heart rate differs between a male or female fetus," confirms Eric Eichenwald, M.D., the chair of the American Academy of Pediatrics (AAP) Committee on Fetus and Newborn. "It's an old wives' tale that has been passed down that has no basis in science."
What doctors do know is that fetal heart rate can change depending on how far along you are: A healthy rhythm increases from 110 beats per minute at week 5 of pregnancy to 170 beats per minute at week 9, then gradually reaches an average of about 150 beats per minute by week 13.[4]
Heart rate can also fluctuate by up to 25 beats per minute throughout the day.[5] "The heart rate may be higher during times of relative excitement, such as after physical activity or if the pregnant person has recently eaten, and relatively lower during rest or sleeping, " Dr. Feigal says.
Some moms in the What to Expect Community have anecdotal evidence debunking the theory: "I have two boys, and [heart rate] was always over 150," says danik1990.
"My best friend had a boy and his heart rate started high as well," adds justmovingthrough.
Sex hormones may play a role in fetal cardiac development, according to the newer research. Testosterone, for example, might create changes in the body that cause an increase in blood pressure — but this doesn't seem to cause a detectable difference in heart rate.
"I can understand why the myth exists," says Catherine Caponero, D.O., an OB/GYN at the Cleveland Clinic, in Cleveland, Ohio. "Parents are so excited to know more about their baby and envision their future. The heart rate, while easy to obtain, unfortunately is not an accurate data point to predict a baby's sex."
Better ways to find out your baby's gender
While there's no way to know your baby's gender from the fetal heart rate, there are more reliable tests that can determine the sex. These include:
- Noninvasive prenatal testing (NIPT): This blood screening analyzes your baby's DNA to determine the risk of genetic disorders. Doctors don't specifically use it to find out a baby's sex, but the results will reveal whether you're having a boy or girl with around 99% accuracy. It's one of the earliest diagnostic tests, done as early as 9 weeks. That's right around when you would first detect a heartbeat!
- Chorionic villus sampling (CVS): This test, which is typically done between weeks 10 and 13, analyzes a small tissue sample from the placenta to look for chromosomal disorders. Like the NIPT, it isn't specifically used to determine sex, but the results can reveal the sex.
- Amniocentesis: Also known as an amnio, this prenatal screening is used to detect chromosomal disorders, usually between weeks 15 and 20 of pregnancy. It can also reveal the sex.
- Anatomy scan: This ultrasound, which is done around week 20, will analyze your baby's anatomy to make sure everything is developing correctly. If you haven't done the NIPT, CVS or amnio, this is when you'll likely learn whether you're having a girl or a boy.
"As human beings, we're always looking for patterns to help us predict and prepare for what is going on around us," says Dr. Feigal. "There are widely held beliefs that how a pregnant person carries their weight in their belly, or what foods they crave, or how much morning sickness they have can predict the baby's sex. Although it's fun to guess, and you have a 50% chance of being correct, none of these methods have been proven to be more accurate than chance."
Bottom line: As hard as it may be to wait, rest assured that you'll learn whether you're having a boy or girl soon enough.
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