Key takeaways
- The earliest you can find out the sex of a baby is at around 10 weeks via a blood test. Anatomy scans during the second trimester are also a popular option.
- However, no method of determining a fetus’s sex is 100% accurate. Sometimes, it is not possible to tell the sex based on an ultrasound.
- There are many myths about how to predict the baby’s sex via nonmedical methods, but none have scientific evidence to show they work.
Finding out a baby’s sex can be exciting for expecting parents. In some cases, it can also be medically useful for determining the risk of certain hereditary conditions.
However, all methods of assessing the fetus’s sex have limitations. In this article, learn when people can learn the sex of a developing baby, which tests are most accurate, and more.
People used to have to wait until the midpoint of pregnancy, in the second trimester, when the genitals become visible on an ultrasound scan. Many still choose this option.
However, today, it is sometimes possible to learn the sex of the fetus by having a blood test at around 10 weeks.
Neither of these methods is 100% accurate. The only way to find out for sure, for most people, is to wait until the baby is born.
An exception to this is people who use in vitro fertilization (IVF) to choose their baby’s sex.
Below are the methods doctors use to determine the sex of a developing baby.
Noninvasive prenatal testing
Noninvasive prenatal testing (NIPT) uses bloodwork to assess the risk of a several genetic disorders. NIPT can also identify the sex, because the test scans for the presence of a Y chromosome.
Most humans have a pair of chromosomes that determine their sex: XX or XY. Most fetuses with XX chromosomes develop female reproductive organs, while most with XY develop male reproductive organs.
In the United States, the American College of Obstetricians and Gynecologists (ACOG) recommends that doctors offer all pregnant people NIPT testing.
However, in many other countries, NIPT is limited to certain populations, such as those with high-risk pregnancies.
Second trimester anatomy scan
A second trimester anatomy scan is a detailed ultrasound that helps a doctor or ultrasound technician gain insights into the fetus, the location of the placenta, and the health of the pregnancy.
Doctors usually schedule it around week 20 of the pregnancy. At this time, the developing baby is typically large enough for a clinician to see the genitals.
However, health professionals cannot always detect the sex with an ultrasound if the fetus is too small, in an atypical position, or something obstructs their view of the genitals.
When this happens, it may be possible to try again at a future scan.
More invasive tests
If an anatomy scan shows potential problems with the fetus, or a family has a strong history of certain genetic conditions, a doctor may recommend more invasive testing methods.
Amniocentesis and chorionic villus sampling (CVS) are two methods that can produce a fairly accurate result because they involve looking at the sex chromosomes.
According to Planned Parenthood, both amniocentesis and CVS both involve taking samples of genetic material from inside the uterus.
Although these tests can accurately predict the sex of the developing baby, doctors only carry out these tests to identify chromosomal conditions, such as Down syndrome.
Both tests can cause serious complications, so a person should not choose either method unless there is a medical reason to do so.
While tests for a fetus’s biological sex are fairly accurate, the results are not always clear-cut.
NIPT blood testing
NIPT tests for chromosomes, which are often an indication of a fetus’s sex, but there can be exceptions.
One reason this can happen is placental mosaicism, which is when the chromosomes of the placenta do not match the fetus.
Another possibility is that the genitals may develop differently to what the chromosomes might suggest.
While chromosomes are determined right at the start of pregnancy, the reproductive organs develop later on. Many factors can influence their development.
In some cases, fetuses with XX chromosomes possess a large clitoris that is more like a penis. Conversely, a fetus with XY chromosomes may have a small penis that resembles a clitoris.
Rarely, fetuses have chromosome combinations beyond XX and XY.
All of the above variations are examples of being intersex, which is an umbrella term for a range of different types of sexual development and conditions that affect it.
According to Planned Parenthood, estimates suggest that around 1 to 2 in 100 people in the United States are intersex.
Ultrasound
In contrast to NIPT, ultrasounds look at the external genitalia of the developing baby. This means they cannot reveal information about chromosomes.
Additionally, while ultrasounds often give health professionals a good idea of the sex, they can be incorrect.
Home prenatal sex tests aim to identify Y sex chromosomes in the pregnant person’s blood. If they are present, the results indicate the fetus is likely male. Otherwise, they indicate the fetus is likely female.
These tests often promise very high rates of accuracy. However, they may have a higher potential for human error because of contaminated or inadequate blood samples.
For example, if someone with a Y chromosome handles the test, their DNA may affect the results.
There are many other myths about the signs a fetus is a specific sex, ranging from the shape of the pregnant person’s belly to their food cravings. There is no scientific evidence to support these prediction methods.
It is important to note that, while biological sex is important in a baby’s development, it cannot tell parents what their child’s personality or interests will be.
It also does not necessarily correspond to gender. Although people often use the two terms interchangeably, sex and gender have different meanings.
Sex refers to the combination of chromosomes, hormones, and reproductive organs that dictate sexual development.
According to the
Not everyone identifies with these norms, or the gender they were assigned at birth. Some identify with a different gender, a more flexible definition of their own gender, or reject the concept of gender entirely.
Furthermore, no prenatal sex testing is 100% accurate. Human error, unusual chromosomes, and inaccuracies all mean there is always a possibility of a surprise at birth, or as the child grows up.
Predicting the sex of a fetus is becoming much more accurate. Still, even with the most accurate methods, there is room for error.
People who want to know the sex of their baby should discuss the risks and benefits of each option with a doctor.