From the minute you learned you were pregnant, you probably wondered whether you’re having a boy or a girl and you may even have a strong preference one way or the other. Read on for the science-based and just-for-fun ways that you can learn whether your baby will be a daughter or son before birth. Regardless of the methods you try before birth, eventually your baby will be born, at which point it is much easier to determine whether baby is a boy or girl.
The earliest ways to find out whether you are having a girl or boy focus on genetic testing. If you are pregnant by in vitro fertilization, you may already know the sex of your baby at implantation. If you are pregnant by intrauterine insemination or typical sexual reproduction, you probably have to wait a little bit longer to find out.
One of the earliest genetic tests is the cell-free fetal DNA test. Not everyone has this test during pregnancy, but you can speak to your care provider about it if you are interested. If you choose to have this test, sometime between 10 and 12 weeks of pregnancy, your care provider will collect blood from you. By 10 weeks, your blood plasma contains some of baby’s DNA, which a lab will then analyze for the presence of sex chromosomes—those bundles of DNA that determine whether a fetus is male or female. Female fetuses have two X chromosomes, while male fetuses have one X and one Y. You can read more in this blog post about how this test works and what some of the risks are.
Another genetic test that can reveal baby’s sex is chorionic villus sampling or CVS. During CVS, your provider will collect a small sample of the developing placenta, which shares genetic information with your baby. This test usually happens between 10 and 13 weeks and is generally offered after something comes up on the cell-free fetal DNA test or if there are family risk factors for some genetic diseases. 
Amniocentesis is the final genetic test that is commonly used in pregnancy. Amniocentesis involves analyzing the genes of cells collected from a small amount of amniotic fluid, the liquid that baby floats in inside your uterus. This test is the most accurate way to tell whether your baby is a boy or girl, and usually performed between weeks 15 and 18 of pregnancy. It’s unlikely that you would have an amniocentesis unless your care provider has other concerns about your baby’s health. 
Another evidence-based method to determining your baby’s sex is ultrasound. In this non-invasive test, a technician uses a wand than transmits high frequency sound waves into your body, which reflect back from your baby and are then interpreted by a machine to generate images.  By about 18 weeks, your baby’s male or female genitalia is present and a clinician can interpret the ultrasound images to determine whether you are having a boy or girl. Unlike the genetic tests mentioned above, this technique is open to some level of interpretation by the person looking at the images, so mistakes can happen.
Just-for-fun Gender Reveal Methods
Before modern medicine, people had all kinds of ideas about how a pregnant woman’s behavior and body could reveal the sex of her baby. Some fun examples include: predicting baby’s sex based on the mother’s dreams, how high up baby looks in mom’s body, whether the mother-to-be has bad morning sickness or not, and what foods mom craves during pregnancy.  In this blog post, you can read about some other ideas, including the Chinese Gender Chart. The Chinese Gender Chart predicts gender based on the lunar age of the mother at the time of conception. If you are interested in predicting the sex of your baby based on your lunar age, there are plenty of websites online that will help you do so (here is one example). These just-for-fun methods are right about 50 percent of the time, exactly what you would expect given that about half of babies born are boys and half are girls. Even though you might not get reliable information from this kind of speculation, it can be really fun to ponder who your baby will be when they finally join you.
- Mayo Clinic, Chorionic Villus Sampling
- WebMD, Pregnancy and Amniocentesis
- How Stuff Works, Ultrasound
- Mental Floss, 9 Historical Methods for Determining the Sex of an Unborn Baby