The idea that a baby’s heart rate can predict sex is a myth. In fact, there seems to be little difference in the average beats per minute between males and females.
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, research into this topic says heart rate is not a reliable indicator of your child’s sex.
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.
This article examines what research has discovered about heart rate and the sex of your baby.
Research has found no significant difference between male and female heart rates during early pregnancy.
- A
2023 review of studies found that fetal heart rate is not a reliable early predictor of a baby’s sex. - A
2016 study also found no significant difference between female and male fetal heart rates during the first trimester. - A
2018 study that used a cardiotocograph (cCTG) to assess male and female fetal heart rates found that male fetuses had a lower baseline fetal heart rate and greater variability compared to female fetuses. However, the absolute differences were small and not estimated to be of major clinical significance.
A 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.
Though heart rate measurements may not reveal your baby’s sex, there are plenty of other tests that can tell you your baby’s sex before you deliver. These include:
- cell-free DNA tests
- genetic testing
- ultrasounds
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 of your pregnancy.
The main goal of these tests is not to determine the sex of your child. Instead, they screen for possible genetic abnormalities.
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.
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 people 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.
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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