When and how can I find out my baby's sex?

When and how can you find out your baby's sex?

From that first positive pregnancy test, virtually every expecting mom wonders whether they're having a girl or a boy. And that's how the myths developed – that you can tell the sex of your baby based on how you're carrying, how fast the baby's heart rate is, or even which way a ring suspended over your belly swings!

While occasionally an old wives' tale shows some merit (women carrying girls may be more likely to have severe nausea during pregnancy, for example), most have zero scientific basis. Even moms who feel sure they know the sex of their baby based on intuition are wrong half the time.

So when and how can you find out your baby's sex for sure? Here are the options during pregnancy.

IVF with sex selection

If you have preimplantation genetic testing during in vitro fertilization (IVF), your embryos are tested for genetic or chromosomal abnormalities and sex. Preimplantation genetic testing is almost 100-percent accurate in determining the sex of the embryos. In fact, it gives you the opportunity to choose the sex of your baby. But if you have embryos of both sexes placed in your uterus, you won't know which one(s) implant.

NIPT

You can find out your baby's sex if you have noninvasive prenatal testing (NIPT), a blood test that can detect Down syndrome and a few other chromosomal conditions starting at 10 weeks of pregnancy. It also looks for pieces of the male sex chromosome in your blood, which can be used to determine whether you're carrying a boy or a girl. (If you're having the test, tell your doctor whether or not you want to know the sex of your baby.)

This test is available to all pregnant women, and the results come within a couple of weeks. Ask your provider about the test if you're interested and they haven't offered it.

CVS

Some women find out their baby's sex from a genetic test called chorionic villus sampling (CVS), which is done to determine whether a baby has a genetic disorder or a chromosomal abnormality.

CVS is usually done between 10 and 13 weeks and can reveal the sex of your baby in a day or two. The procedure involves taking cells from the placenta and sending them to a lab for genetic analysis. Because it uses genetic information, it can tell you the sex of your baby.

Women who aren't at increased risk of genetic and chromosomal problems don't typically have CVS, in part because these tests are invasive and may carry a small risk of miscarriage.

Amniocentesis

Amniocentesis is a genetic test similar to CVS. It can detect birth defects and chromosomal abnormalities such as Down syndrome.

The procedure is usually done between 15 and 20 weeks, though it can be done after this timeframe, too. It can tell you the sex of your baby in a couple of days. (So tell your doctor if you don't want to know.)

Amnio is available for all expecting moms, but it's generally only used for women at increased risk of genetic and chromosomal problems. Like CVS, the test is invasive and carries a small risk of miscarriage.

Ultrasound

Many pregnant women find out their baby's sex (if they choose to know) during their mid-pregnancy ultrasound, which is usually done between 18 and 22 weeks. Ultrasound uses sound waves to create pictures of your baby, and the technician will be able to tell your baby's sex by looking at their genitals.

Although a baby's penis or vulva begins forming as early as 6 weeks, boy and girl babies look very similar on ultrasound until about 14 weeks, and it can still be hard to tell them apart at this point.

While some studies have reported that genitalia can be seen as early as the first trimester, in almost all cases it can't be accurately determined until the mid-trimester ultrasound. Even then, sometimes it's difficult for the technician to get a clear view of the baby's genitals. Your baby may "hide" them in a position that obscures a good view, for example. In this case, you may be able to find out if you have another ultrasound later in your pregnancy.

Do gender predictor tests work?

Most gender predictor tests (including our Chinese Gender Predictor tool) are just for fun and offer only a 50/50 chance of being accurate – the same as guessing.

At-home gender kits (available mostly online) test blood or urine to predict your baby's sex, but there's no scientific evidence that these tests really work.

SneakPeek and Peekaboo, for example, test blood samples and claim greater than 99 percent accuracy as early as 6 weeks. No independent studies support any of these claims.

Some kits test urine rather than blood. The GENDERmaker test, for example, is a urine-based gender predictor kit that tests as early as 6 weeks of pregnancy. But urine-based kits generally don't claim accuracy, for good reason. Urine doesn't contain any information (such as DNA or sex hormones) that could predict the sex of a baby.

"If you want to use a gender predictor test for fun, there's no harm," says Layan Alrahmani, M.D., an ob-gyn and maternal-fetal medicine specialist in Chicago. "But if you want reliable results, talk with your healthcare provider. They can tell you the best way to find out the sex of your baby, depending on your circumstances."

Note: We're using the words gender and sex interchangeably, because many people do when talking about their child's sex. However, the two are not the same. Sex is usually assigned at birth based on biological characteristics, such as the genitals. But sex designation may not match a person's gender identity (based on feelings and behaviors) that they assume later.

Learn more:

• Does sex selection work?
• Folk wisdom about choosing your baby's sex
• When are sex organs formed?