Using Fetal Heart Rate to Predict the Sex of Your Baby

Stethescope listening to pregnant belly
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Being pregnant brings about a host of questions, including how (and how soon) you can determine the sex of your baby. There are multiple methods used to determine a baby's gender, some more reliable than others. Using fetal heart rate as a way to determine a baby's gender is based in myth, despite being believed to work for many years.

Detecting Your Baby's Fetal Heart Rate

The most common way to listen to the fetal heart beat is with a hand held Doppler device.

This listening device uses ultrasound technology, sound waves, to project the sound of your baby's heartbeat through a speaker. This means that you and those with you can hear the galloping beats of your baby's heart. The Doppler is usually used from about ten to twelve-weeks gestation until labor begins. It can also be used in labor as a type of fetal monitoring.

However, your baby's heart will begin to beat between the fifth and sixth week of pregnancy. The best way to hear the baby's heartbeat during this time is via an ultrasound. This ultrasound may be a vaginal ultrasound or a transabdominal ultrasound, depending on the age of the pregnancy, your body shape, the amount of subcutaneous fat, and the location of the uterus. If you can't hear the heartbeat, there are common reasons why, not all of them miscarriage.

The first heart beats were rarely seen, but as ultrasound technology in the first trimester has improved we are able to see more about the pregnancy and baby earlier.

Usually, you can see a few flickering pixels on an ultrasound screen between six and seven weeks gestation.

At this point, the heart rate of your baby is usually slower than it will be in the coming weeks. However, by the time you are eight to ten weeks pregnant, your baby’s heart will be beating about 170 to 200 beats per minute (bpm).

This will gradually slow down to the normal fetal heart rate range of 120 to 160 bpm during the middle part of pregnancy until the end.

Note that heart rates fluctuate at all stages of life. If your baby moves, his or her heart rate goes up, just as your heart rate does with movement. So, we aren't looking at your baby's heart rate fluctuation, but rather his or her average resting heart rate.

Fetal Heart Rate Differences Between Boys and Girls

Do these heart rate ranges differ between boys and girls in the womb? The short answer to this question is no, there is no difference in a boy's and girl's heartbeat during pregnancy. There are no known ways to tell the sex of your baby based on heart rate alone.

This is true at all points during pregnancy. It doesn't matter if you use ultrasound or a fetal heart monitor—there is no correlation between the sex of the baby and the normal fetal heart rate. Multiple studies putting the question to the test have found no correlation.

How Did the Baby Heartbeat Gender Myth Get Started?

First, it is important to note that since the beginning of time, we have tried to determine gender before birth by tracking differences in pregnant women and then looking at the sex of the babies born.

This is where the many versions of folklore have started and proliferated. While these folklore accounts are not based in fact and do not hold up in the scientific literature, there are plenty of them. Everything from using a ring to using an ancient Chinese gender chart have been used.

While there is not a definitive answer as to where the heartbeat myth started, a bit of history can be useful at giving us some clues. To start, a British study done in 1998 notes that "There is a widespread but erroneous view among the lay public that there is a difference in the baseline fetal heart rate between male and female fetuses." The scientists who conducted the study clearly assumed that the notion originated in folklore, but a scan of the medical literature over the past thirty years suggests otherwise.

For example, a similar study done eighteen years earlier refers to "the hypothesis" that the sex of the fetus can be determined by fetal heart rate, indicating that the idea had already won some credence within the medical community itself by that time. In fact, references to the hypothesis can be found in scientific studies dating back to 1969.

Labor and delivery nurses would also offer a nugget of information and would tell patients in labor that a fast fetal heart rate was a girl and a slower fetal heart rate was a boy. They based this on their experience alone and there was no science behind what they were saying. What sets the fetal heart rate myth apart is that it sounds like it might be based on medical fact and it was perpetuated by well meaning nurses who had no science to back up their assumptions.

How Is Your Baby's Gender Decided?

As a point of looking at genetic differences, it's important to know when the sex of your baby is determined and how. Your baby gets a set of DNA from the mother and the father. The female, being XX, can only contribute an X to the DNA of the baby. The male is XY and can contribute either an X or a Y. This is determined as soon as the egg and sperm meet, but the outward appearances of the baby will not show external genitalia until later first trimester.

How Genetic Testing Plays Into Sex Determination

Plain curiosity isn't always the reason parents want to know if they're having a boy or girl. In some cases, if the family has a sex-linked genetic disorder, finding out the sex of the baby can allay the fears of the family or let them know what the odds are that their baby is in need of help.

As science perfected genetic testing in the form of the amniocentesis and the chorionic villus sampling (CVS), parents were able to know the sex of their baby and have a better idea for risk of genetic conditions. The problem is that these tests are invasive, meaning that they can be potentially life-threatening to the baby. As such, they are reserved for families who have a high risk of genetic anomalies.

Note that although these tests are a more reliable method of sex determination, unlike the fetal heart rate myth, they are not done simply to find out a baby's gender. That information is a bonus.

More Reliable Methods for Learning Your Baby's Gender

Ultrasound

Although heart rate estimates through ultrasound aren't reliable for determining a baby's gender during pregnancy, ultrasound around the midpoint of pregnancy is currently the most common way that families find out the sex of their baby.

Rather than focusing on heart rate, an ultrasound is used to look at the anatomy and physical health of the baby. Certainly, the external genitalia fall into that category. Ultrasounds are done in the later part of the first trimester and early second trimester. Even before the external genitalia of boys and girls is very distinct, there are accurate ways to tell the sex of the baby based on the direction the genital tubercle points and a few other indicators. And although ultrasounds are sound science, note that there can be mistakes made.

There is also a very early look at determining boys from girls via ultrasound between six and ten weeks using the placement of the placenta. This is known as the Ramzi Method and although it it has some science behind it, it is not currently accepted as perfected. It is not offered in many practitioners' offices and is considered "complimentary" to traditional methods to determine the sex of your baby.

Cell Free DNA

In recent years, cell-free DNA tests, known as non-invasive prenatal testing (NIPT), have become very accurate at predicting the sex of the baby without the risks of the invasive prenatal tests. These tests use maternal serum, the mother’s blood, to look for fetal DNA in the blood.

These tests, while not potentially physically harmful to the baby, are often not covered by insurance and need to be paid for out of pocket. They are also designed to be a way to screen for genetic issues and the ability to find out the sex of the baby is an added bonus rather than the main focus of these tests.

There are a number of these tests, like Harmony and MaterniT21 Plus, available. Your doctor or midwife can give you information about which test might be right for you and what you need for your pregnancy. Again, the cell-free DNA tests are screening, whereas the amniocentesis and CVS are diagnostic. A screening exam simply means that you are at a higher risk of a problem, not that your baby absolutely has a genetic issue.

A Word From Verywell

Finding out if you are having a girl or a boy is a very exciting part of pregnancy, but be very careful that you do not fall prey to folklore methods for determining your baby's sex. The fetal heart rate myth is one of them, with no scientific basis.

Use more reliable methods, like ultrasound, to help you determine whether you are expecting a girl or a boy. Your doctor or midwife can help you figure out what test will help you figure out the sex of the baby you're carrying at the earliest point in gestation possible, with the highest degree of accuracy, using the test that is most appropriate for you and your baby.

Sources:

Bracero LA, et al. First-trimester fetal heart rate as a predictor of newborn sex. J Matern Fetal Neonatal Med. 2016 Mar;29(5):803-6. doi: 10.3109/14767058.2015.1019457. Epub 2015 Mar 10.

Doubilet PM, Benson CB. Embryonic heart rate in the early first trimester: what rate is normal? J Ultrasound Med. 1995 Jun;14(6):431-4.

McKenna D, Ventolini G, Neiger R, Downing C. Gender-related differences in fetal heart rate during the first trimester. Fetal Diagn Ther. 2006;21(1):144-7.

Society for Maternal-Fetal Medicine Publications Committee. #36: Prenatal aneuploidy screening using cell-free DNA. American Journal of Obstetrics and Gynecology. 2015;212:711.

Stamatopoulos N, et al. Prediction of subsequent miscarriage risk in women who present with a viable pregnancy at the first early pregnancy scan. Aust N Z J Obstet Gynaecol. 2015 Oct;55(5):464-72. doi: 10.1111/ajo.12395. Epub 2015 Aug 21.

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