Learning the Gender of Twins: Different Methods & Timing

From the time those little blue lines appear, you never stop wondering who your babies will become. Learning gender is often one of the first moments parents get to share and celebrate. 

When can you find out the gender of twins?

While gender can be predicted earlier in pregnancy via at-home methods, medical confirmation of gender only occurs as early as 10 weeks gestation. Other prediction methods, such as ultrasounds, chorionic villus sampling, and amniocentesis, offer high accuracy results later in pregnancy.

All gender determination methods vary in timing, out-of-pocket cost, availability, risk, and accuracy. 

Trying to navigate the medical terminology and timelines through pregnancy can be challenging.

Reading about the following methods of gender prediction will help you understand your obstetrician’s recommendations and feel more confident in your path. 

Learning the Gender of Your Twins

Technology has developed and allows early insight into gender determination, but what does that look like? 

Ultrasound

Gender can be detected by ultrasound as early as 12 weeks. However, early ultrasound scans are not as accurate as later ones.

Given the increased probability of misgendering during this time, many sonographers will err on the side of caution and recommend waiting until a later scan. 

At 14 weeks, prediction accuracy increases significantly because the genitals are fully developed. Gender determination via ultrasound occurs most often at the fetal anatomy scan around 18 to 20 weeks gestation. 

Blood Test (Non-Invasive Prenatal Testing)

Non-Invasive Prenatal Testing is a blood panel designed to determine the risk of genetic abnormalities.

The NIPT is optional and generally recommended to parents with a family history of chromosomal disorders such as Down Syndrome and Trisomy 13. 

Though this test isn’t specifically designed for gender prediction, it’s 99% accurate when doing so. This method can be slightly more complex for multiples because there has to be a strong enough presence of both babies’ DNA in your blood. 

The NIPT is offered by your obstetrician on or after 10 weeks gestation. This testing isn’t usually covered by insurance unless you’re 35 or older.

With few exceptions to the rule, this forum discusses a few ways you can combat the out-of-pocket cost. 

Amniocentesis

In contrast to Non-Invasive Prenatal Testing, amniocentesis is used primarily for diagnosing chromosomal disorders rather than just predicting the risk.

Between 15 and 20 weeks gestation, your obstetrician may offer amniocentesis based on your predisposition for genetic abnormalities. 

Since this testing method also examines chromosomal patterns, gender prediction is 99% accurate. However, amniocentesis carries risks to the fetus, such as infection, preterm labor, or miscarriage.

For this reason, it’s not recommended or allowed for the sole purpose of predicting gender. 

Chorionic Villus Sampling

This is another genetic testing method that carries a similar risk to amniocentesis. Rather than sampling the amniotic fluid or blood, Chorionic Villus Sampling takes a small piece of each placenta through the vagina or abdomen. 

CVS allows an earlier diagnosis of fetal abnormality and occurs between 10 and 13 weeks gestation.

Due to the risk profile, CVS is not recommended or allowed solely for gender prediction. 

At-Home DIY Testing

At-home gender prediction kits, such as SneakPeek, claim to be able to determine gender at 6 weeks with 99.9% accuracy. These claims are not scientifically supported.

It’s important to remember that results should be confirmed with your obstetrician through standard methods.

Being pregnant with twins will affect both the accuracy and quality of home tests. With identical twins, any presence of a Y chromosome in the mother’s blood or urine indicates two male babies.

However, fraternal twins are capable of being opposite genders. So, the presence of a Y chromosome will not differentiate whether only one or both babies are male. 

Old Wives’ Tales

Before diagnostic tests and ultrasounds, women relied on old wives’ tales to predict gender. You’ll notice that these tales could self-conflict if you have opposite-gender twins.

These stories don’t have scientific backing. However, they still make a great game for your baby shower! 

  • Carrying Position – If you’re carrying high, it’s said that you’re pregnant with a girl, whereas if you’re carrying low, it’s a boy!
  • Morning Sickness – Legend says that a girl will cause nausea and vomiting. A boy will exempt you from this unlucky pregnancy symptom. 
  • The Ring Test – Tie a ring to a strand of your hair, and hold it over your bump. If the ring starts moving in circles, it’s a girl. If it moves in a line, it’s a boy! 
  • Baby’s Heartbeat – Girls are said to have faster heartbeats than boys. If your baby’s heartbeat is above 140, it’s a girl; otherwise, it’s a boy! 
Newborn twins sleeping in a basket.

Who Determines the Gender of the Baby

Gender is determined by the father at the moment of conception when the sperm(s) fertilize the egg(s) with either an X or Y chromosome.

The addition of a Y chromosome creates a male, while the addition of an X chromosome creates a female. 

How Early Can Gender Be Determined By Ultrasound

The earliest gender can be determined via ultrasound is 12 weeks based on the nub theory.

The nub theory uses the angle of growing genitalia to determine gender. An upward angle indicates a boy while a downward angle indicates a girl.

The accuracy of this prediction method relies on several factors, such as fetal positioning, ultrasound method, and the sonographer’s skill level.

Studies show a 75% prediction accuracy that significantly increases at 14 weeks gestation. 

Twin Gender Probabilities

Identical twins occur when one egg is fertilized by one sperm and then divides. Due to this biological process, they will always be of the same gender.

According to the Washington twin registry, female twins are more prevalent than male twins, but the statistic still teeters around 50%. 

Fraternal twins occur when two eggs are fertilized by two separate sperm. This allows for opposite-gender twins.

This formula shows that in fraternal pregnancies there is roughly a 25% chance of having female twins, a 25% chance of having male twins, and a 50% chance of having opposite-gender twins. 

Should I Find Out the Gender of My Baby (Babies!)

Knowing the gender(s) allows you to do exciting things like throwing a gender-reveal party, getting baby items customized, and choosing baby names in advance.

It can also allow time to cope with gender disappointment and help you feel more connected to your babies.

On the other hand, not finding out the gender of your babies has benefits such as reduced exposure to misinformation, not having to abide by gender norms, and the exhilaration of the unknown.

If you opt for the unknown, more careful planning may be needed to make the process less stressful. 

Planning for your twins around gender-neutral themes and creating a list of baby names for each gender are small ways to combat anxiety during pregnancy.

These preparations allow you to plan and build for your babies while maintaining the gender surprise. 

Related Questions:

Are Twins of the Same Gender More Common? 

Yes! Same-gender twins account for roughly 50% of all fraternal pregnancies. Identical twins will always be of the same gender as well.

This means that twins of the same gender are more common across the board, whereas in fraternal pregnancies, opposite-gendered babies are more likely. 

Can Twins Be Missed at 8 Weeks?

Missing a twin at 8 weeks is unlikely but not unheard of. This happens more frequently with monoamniotic and monochorionic twins because they are positioned closely together at all times.

Since there are other indications of twin pregnancy, early ultrasounds are the main culprit. In these rare instances, a second-trimester ultrasound will find the second twin. 

Conclusion

While gender can be predicted through at-home methods as early as 6 weeks, medical confirmation of gender occurs as early as 10 weeks gestation.

Ultrasound scans and blood tests are the primary gender determination tools since they pose little risk to health and lower cost.