What determines the sex of the baby?

The baby’s sex is determined at conception when the sperm and egg combine. The baby receives 23 chromosomes from each parent. One of these pairs determines the baby’s sex: a baby with XX chromosomes is female, a baby with XY chromosomes is male. The external genitalia form around 11 weeks of pregnancy, and an ultrasound can only reveal the baby’s sex after 18 weeks, so many pregnant women and their families turn to unreliable common myths and old wives’ tales to predict the baby’s sex.

Signs you’re pregnant with a boy: 5 common myths 

Everything from changes in your appearance to your eating habits has been linked to a  baby’s sex, but are there really signs you’re having a boy? Some of the most popularly believed pregnancy symptoms and signs of having a boy might not be found in science, but let’s dive in.

#1 Beautiful Hair and Skin Means a Baby Boy

The Theory: Not quite a theory, but a common urban pregnancy legend-girls steal your beauty while boys make you more beautiful. So if you have no pregnancy acne and long, lustrous hair, you’re having a boy.

The Facts: The only thing your baby will be stealing is your heart, regardless of sex. Whether you’re experiencing serious hair glow-up or flashing back to your acne-ridden teen years, the same culprit causes both conditions: hormones. Pregnancy naturally increases your body’s hormone levels to help the fetus grow. Hormones encourage cell growth, healthy placenta development, and more. While these hormones may nourish your baby’s development, they can also result in some physiological changes for you as a pregnant woman, including:

• Thicker, shinier hair – Several key pregnancy hormones, including progesterone, can impact your locks. Progesterone increases natural oil production in your hair glands, giving your hair a luxurious luster while you’re carrying a little one. Estrogen, another hormone that increases during pregnancy, may extend your hair’s growth cycle. This slows natural hair shedding and creates longer, thicker hair during pregnancy.
• Breakouts – Progesterone’s ability to increase natural oil production may also cause acne breakouts. When the skin produces excessive oil, it’s easier for bacteria and grime to settle into pores and cause acne.
• Longer, stronger nails – During pregnancy, your estrogen levels rise higher than any other time in your life. Researchers believe that the increase of this hormone may strengthen your nails and help them grow longer.
• Glowing skin – Pregnancy glow is a rosiness caused by an increase in blood flow to a woman’s face-and really, her whole body. During pregnancy, your blood volume will increase by 40 to 45%. Why the sudden increase in blood? Your vascular system is how your body transfers sustenance from you to the placenta to the growing fetus baby.

But does the sex of your baby affect these hormonal conditions? Nope!

Pregnancy hormones just affect women differently. So you may enjoy longer, stronger hair, or you may have a few more breakouts than you’re used to. The good news (or maybe the sad news if you’re relishing your pregnancy glow-up) is that these symptoms will fade away after your baby is born. So enjoy it while it lasts or, alternatively, remember that these hormonal changes are temporary.

The Verdict: You may experience the effects of hormonal increases like rosy skin or thicker hair whether you’re carrying a lovely little boy or a gorgeous little girl. Though this may not be considered one of the symptoms of baby girl or baby boy pregnancies, extra luscious hair and skin is something to enjoy while pregnant!

#2 Carrying Low Means You’re Having a Boy

The Theory: If your pregnancy belly sits low on your abdomen, i.e. if you’re carrying low, you’re having a baby boy.

The Facts: This theory comes from the assumption that baby boys are heavier than baby girls, and therefore gravity naturally situates them lower on your body. However, boy and girl babies weigh about the same, on average. Here are the average birth weights of newborns from the World Health Organization:

• Newborn baby girls – 7.5 pounds
• Newborn baby boys – 7.8 pounds

While there is a difference of 0.3 pounds between newborn boys and girls, it’s not enough to impact where the baby is situated on your body. In fact, it’s not your baby’s body that determines whether you’re carrying high or low-it’s yours.

A few key factors impact where you carry your baby, including:

• The shape of your uterus – Just like women, uteri come in all shapes and sizes. That’s right, your uterus shape might be slightly different than your mom’s or your gal pals’. And your unique uterus can affect your belly’s shape and where you carry your growing child.
• Your body type – Your unique body shape and type can determine whether you carry the baby high or low.
• Your abdominal muscles – Your ab muscles help cradle your growing belly. So if you have stronger muscles, you will carry higher. Additionally, if you’ve been pregnant before, those muscles may be a little softer and carry your baby a little lower.

Think of your abdomen like a basket with your baby snug inside. The material, shape, and construction of the basket will have more of an impact on your belly’s appearance than your baby.

The Bottom Line: So, is there a difference between boy and girl bumps? The answer is no—your baby’s sex doesn’t impact the position of your baby bump. For more details on how your body affects where you carry your child, check out our blog on pregnant belly shapes and what yours means.

#3 Lower Fetal Heart Rate Indicates a Baby Boy

The Theory: A baby’s heart rate can tell you the  baby’s sex. If the bpm (beats per minute) is lower than 140, you’re having a boy.

The Facts: This theory also links back to the “boy babies are bigger” myth since taller adult bodies tend to have lower resting heart rates. But when we bring science into play, this myth gets double-busted.

Multiple studies have shown that baby heart rates, regardless of gender, tend to be the same. For more details on these studies, you can explore our blog on gender prediction based on heart rate. However, a baby’s heart rate does change based on the current stage of development.

• 5 Weeks – 80-85 bpm-about the same as yours!
• 9 Weeks – From nine weeks and throughout most of the pregnancy, a baby’s heart rate will range between 120-180 bpm.
• The Last 10 Weeks – Before delivery, babies’ hearts slow down just a bit, with bpm landing somewhere between 110 and 160 beats per minute.

For a little context, the normal resting heart rate for adults is 60-100 bpm. While your baby’s heart rate seems a little fast, it’s normal for those little hearts to beat a little quicker. Scientists are still learning why babies’ heart rate changes in the uterus, but they know for a fact that your  baby’s sex doesn’t impact the wonderful, speedy little heartbeat.

The Verdict: Your little one’s fluttering heart is a wonder to listen to-especially with the help of our at-home Baby Heart Monitor-but the baby’s heartbeat alone won’t tell you whether you’re having a baby girl or baby boy.

#4 No Morning Sickness Means a Baby Boy

The Theory: More hormones means more morning sickness and since girls naturally have more hormones, no morning sickness means you’re having a boy!

The Facts: Research has shown that hormone levels in a woman don’t change based on your baby’s sex, it’s the other way around. You have more of an impact on your baby’s hormone levels. Both girl babies and boy babies are born with a high amount of estrogen in their systems thanks to pregnancy hormones. So no, your little girl or boy isn’t causing hormone-induced nausea or vomiting.

But when it comes to morning sickness, the science is… still figuring it out. Multiple studies show contrasting information. Here are the two most recent studies on morning sickness and a  baby’s sex.

• Sweden (1999): Researchers studied over a million births and found that women who experienced severe morning sickness were slightly less likely to have boys (44.3% boys vs. 55.7% girls). The study’s lead author even compared the accuracy of using morning sickness to predict sex to “tossing a coin.”
• Iran (2013): In a smaller study of about 2,400 pregnancies, women who reported morning sickness were more likely to give birth to boys—roughly 79% of those with nausea had sons.
• United Kingdom (Ongoing): Current research on hyperemesis gravidarum—an extreme form of morning sickness—aims to better understand whether there’s any connection between severe nausea and a baby’s sex, though results are still pending.

The Verdict: Do you get morning sickness with a boy more than a girl? Morning sickness might be included as one of the signs you are pregnant with a boy, but the scientific jury is still out. More studies need to be conducted to reach concrete conclusions on this phenomenon.

If you’re in your first trimester and experiencing some stomach issues associated with morning sickness, you’re not alone. Check out our guide on natural cures for first-trimester tummy troubles.

#5 Your Feet Have Been Cold

The Theory: Having icy-cold feet is a sign you’re having a boy.

The Facts: If your feet have felt cold during your pregnancy this could stem from numerous causes. Having cold feet could be simply due to cold weather or the temperature of your home. The lower temperature of your feet is most likely due to hormonal changes. The autonomic nervous system can be affected by pregnancy and cause decreased blood flow to the lower extremities, especially the feet.

Other less common causes of cold feet could be:

• Poor circulation
• Low blood pressure
• Anemia
• Hypothyroidism

Speak with your doctor if you feel like you’re experiencing any of these conditions.

Of these conditions, Anemia is the most prevalent, with approximately 14% of American women experiencing anemia during their pregnancy. Anemia is most likely to occur in the second or third trimester when the baby is growing rapidly. But don’t panic, your doctor should be checking for anemia throughout your pregnancy.

The Bottom Line: Cold feet do not indicate the sex of your baby. Pregnant women who experience cold feet give birth to boys and girls. So put on a pair of fuzzy socks and keep an eye on your symptoms if you feel the change is unusual.

Scientific signs you might be having a boy 

While most “boy or girl” predictions lean on fun folklore, some research has explored subtle physical and biological indicators that may hint at a baby’s sex. These findings aren’t foolproof—but they do show how fascinating the science of pregnancy can be. Here are a few research-backed clues that might suggest you’re carrying a baby boy:

• You’re eating a bit more—but not gaining extra weight: Studies suggest women carrying boys may consume around 10% more calories than those carrying girls, yet show no significant difference in overall weight gain. While it’s a small change—roughly an extra 250 calories per day—researchers believe it may be tied to the higher energy demands of male fetuses.
• You’re more prone to food aversions: Some studies indicate that you may experience stronger or more frequent aversions to certain foods during boy pregnancies. This could be related to hormone fluctuations or immune system responses that differ slightly when carrying a male fetus.
• You’ve started snoring more often: Increased snoring can sometimes be linked to higher pregnancy weight distribution and nasal congestion, which research shows may occur more often in women carrying boys. It’s not a guaranteed sign, but it’s one of those small shifts that might be connected to hormonal differences.
• You’re diagnosed with gestational diabetes: Research has shown that carrying a boy can slightly raise the likelihood of developing gestational diabetes. Experts think this may be due to how male fetuses influence maternal insulin sensitivity and metabolism during pregnancy.

How to find out your baby’s sex

Finding your baby’s sex early into your pregnancy can be achieved through various methods. Some of these options are:

Ultrasound

• Pros: A non-invasive practice that shows a screen image of the fetus in the womb.
• Cons: Performed later in the pregnancy (18-20 weeks)

Chorionic Villi Sampling (CVS)

• Pros: Can test for genetic conditions of the fetus.
• Cons: Performed in the first trimester. Invasive testing process, risk of miscarriage, bleeding, infection, etc. and results are not always accurate.

Amniocentesis

• Pros: Can test for genetic conditions of the fetus.
• Cons: Performed in the second trimester. Invasive testing process, risk of miscarriage, bleeding, infection, etc. and results are not always accurate.

DNA blood test

Pros: A simple, non-invasive test that analyzes fetal DNA found in the bloodstream, with at-home options available.
Cons: While highly accurate, this test focuses solely on genetic sex determination.

Boy or Girl? Discovering Your Baby’s Gender with SneakPeek

Your glow, morning sickness, or even the acclaimed pencil gender test may not reveal your baby’s sex, but you can see signs of having a boy with the SneakPeek Early Gender DNA Test, the only test that lets you know as early as 6 weeks into pregnancy.

Gender blood tests conveniently allow you to get accurate results with minimal invasiveness, searching for traces of male DNA in your bloodstream. Since you only have female DNA, the presence of male genetic material points to one thing—a blue nursery and a beautiful baby boy! This simple, safe, and intuitive gender prediction test can be conducted in the comfort of your own home, and you receive results soon after your test sample arrives back at SneakPeek Labs. Now it’s time to brainstorm unique baby boy names!

Stop reading the signs and start finding answers with SneakPeek.

FAQs on boy pregnancies

Is there a higher chance of having a boy than a girl?

We’ve covered the signs of a male pregnancy, but what are the chances of having a boy? Statistically, the odds are nearly even—about 51% of babies are boys and 49% are girls. The baby’s sex is determined at conception, based on whether the sperm carries an X or Y chromosome. Despite myths about timing or diet influencing the outcome, it’s purely biological.

Can you tell if it’s a boy or girl at 6 weeks?

The signs of a boy pregnancy at 6 weeks may be hard to spot, but there are methods of finding out the sex at this point. Traditional ultrasounds can’t reveal the baby’s sex until around 18–20 weeks, but DNA blood testing can offer answers as early as 6 weeks with over 99% accuracy. It’s a fast, science-backed way to satisfy early curiosity.

Do you feel different when pregnant with a boy?

Every pregnancy is unique, and no consistent symptoms have been proven to indicate a baby’s sex. Some people report feeling less nauseous or more energetic with boys, but research doesn’t support a reliable pattern. Hormones, health, and lifestyle influence how you feel far more than whether you’re carrying a boy or a girl.

Is hCG higher with boys or girls?

Some studies suggest human chorionic gonadotropin (hCG) levels may be slightly higher with female fetuses, but the difference is too small to predict sex accurately. These levels naturally rise and fall throughout pregnancy and vary widely from person to person. Elevated or lower levels are normal and reflect timing and physiology—not whether your baby is a boy or a girl.

Is fatigue worse when pregnant with a boy?

Fatigue is one of the most common pregnancy symptoms, and its severity depends on hormones, rest, and overall health—not the baby’s sex. While some research has explored possible differences, findings remain inconclusive. Feeling extra tired is simply your body adjusting to pregnancy, not a sign of whether you’re expecting a boy or a girl.