The idea that a baby’s heart rate can predict this sex is a myth. In fact, there seems to be little difference in the average beats per minute between males and females.

There are lots of old wives’ tales surrounding pregnancy. You may have heard that your baby’s heart rate can predict its sex as early as the first trimester. If it’s over 140 bpm, you’re having a baby girl. Below 140 bpm, you’re carrying a boy.

The truth is, your baby’s heart will likely start beating sometime around week 6 of your pregnancy. You can even see and measure this flicker of light on an ultrasound. The beats per minute (bpm) start at a slow 90 to 110 bpm and increase daily. They continue to increase until they peak around week 9, between 140 and 170 bpm for boys and girls alike.

Still, you can find lots of forum topics across the web on this subject. Though many women swear heart rate clued them in, the overall results are mixed at best. For example, on, most women reported that this myth did not work. Some even shared that their boys actually had higher heart rates, while others shared that their girls had lower beats per minute.

Here’s what the research says about heart rate and the sex of your baby.

What research says about heart rate and gender

In a study published by Fetal Diagnosis and Therapy, researchers examined 966 sonograms from women who were all under 14 weeks gestation. They repeated this process again in the second trimester between weeks 18 and 24, when baby’s sex can also be determined via ultrasound. By this point, only 477 women still met their study criteria. Of these pregnancies, 244 were revealed to be girls, while 233 were revealed to be boys.

Did heart rate help predict gender? The average heart rate for baby boys in the first trimester was 154.9 bpm (plus or minus 22.8 bpm) and for baby girls it was 151.7 bpm (plus or minus 22.7 bpm).

In other words, this myth is busted. There was not a significant difference between male and female heart rates during early pregnancy.

When is sex determined?

Your baby’s sex is set as soon as the sperm meets the egg. Sex is determined at conception, before you even know you’re pregnant. The genitals won’t develop for some time, but your little one inherits either an X or Y chromosome.

In most cases, little girls carry an XX pattern of genetic information, while little boys carry an XY.

You might also be surprised to learn that your baby’s genitals don’t develop immediately. In fact, boys and girls look relatively the same four to six weeks after gestation. They start to differ between 10 and 20 weeks.

Tests that reveal gender

Though heart rate measurements may not tell you if you should buy pink or blue nursery paint, there are plenty of other tests that can tell you your baby’s sex before you deliver.

Cell-free DNA

Blood tests called cell-free DNA tests have cropped up over the last several years. You can get one as early as around week 9 in your pregnancy. The main goal of these tests is not to determine the sex of your child. Instead, they screen for possible genetic abnormalities. Your child’s sex chromosomes are among all that other genetic information.

Compared to similar screens (Verifi, MaternitT21, Harmony), Panorama claims a 100 percent accuracy rate with determining fetal sex. Detecting the presence (or absence) of the Y chromosome ultimately reveals the sex.

It’s important to note that this test is not recommended for women carrying multiples, using donor eggs, or those who have received a bone marrow transplant. Since Panorama is a screening test, the results regarding genetic abnormalities could be false positives or false negatives.

Any possible diagnosis you receive should be confirmed with further testing.

Genetic testing

A little later on in your pregnancy, your doctor may give you the option of having an amniocentesis or chorionic villi sampling (CVS). These tests look for genetic abnormalities just like the cell-free DNA. As a result, it can reveal the sex of your baby.

These tests are more accurate than the cell-free blood tests, but also more invasive and carry some miscarriage risk.

  • A CVS test is typically performed somewhere between weeks 10 and 13.
  • An amniocentesis is usually performed later, between weeks 14 and 20.

Before you sign on to find out your baby’s sex this way, pause for a moment. These tests do carry potential risks to the baby, so they aren’t usually recommended unless you:

  • have received positive results from a cell-free DNA test
  • had a chromosomal condition in another pregnancy
  • are over age 35
  • have a family history of a certain genetic disorder

The ultrasound

The most common time when couples find out the sex of their babies is between weeks 18 and 20. Many doctors perform an anatomy scan around this point in pregnancy to examine your baby’s features and inner workings from head to toe.

During this noninvasive test, your technician will put gel on your tummy and use a probe to take photos of your baby. Your little one will have a series of measurements to ensure they are growing well. The tech will also look at the body’s systems, the fluid levels around the baby, and the placenta.

You’ll likely be given the option to find out the sex and get some photos to hang on your refrigerator. The tech can often see the baby’s genitals clearly on the screen and make a pretty solid, educational guess. Occasionally, due to the baby’s position, finding out the sex may be difficult.

Bottom line

Science says that heart rate in early pregnancy is not a reliable indicator of your baby’s sex. So keep guessing along with your friends and family. Soon enough, you should be able to confirm boy or girl at your anatomy ultrasound — or at the very least, on your delivery day.

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