Health Library
Health Library

    Pregnancy signs and symptoms that you’re having a boy or a girl

    Updated 26 September 2023 |
    Published 02 January 2019
    Fact Checked
    Medically reviewed by Dr. Angela Jones, Obstetrician and gynecologist, attending physician, Jersey Shore University Medical Center, New Jersey, US
    Written by Olivia Cassano
    Flo Fact-Checking Standards

    Every piece of content at Flo Health adheres to the highest editorial standards for language, style, and medical accuracy. To learn what we do to deliver the best health and lifestyle insights to you, check out our content review principles.

    Are there pregnancy signs to look out for to know if you’re having a boy vs. a girl? Here’s what you need to know. 

    Key takeaways 

    Why find out the sex of your baby before delivery?

    While your top priority is, of course, to have a healthy pregnancy, it’s only natural to be curious about your baby’s sex when you’re expecting. Many people want to know their baby’s sex from the moment they get a positive pregnancy test — after all, nine months is a long time to wait before meeting your little one. 

    For many soon-to-be parents, learning the baby’s sex is a matter of practicality. Maybe you’ve been thinking about unisex baby names, or maybe discovering your baby’s sex could help you decide on a name and prepare for their arrival. Announcing your baby’s sex to loved ones can feel like a big milestone, and some parents use their child’s biological sex to decide what color clothing and nursery decorations to buy. 

    When does your baby develop their biological sex? 

    The process through which sex is determined is called human sexual differentiation. You probably won’t find out your baby’s sex until a few months into your pregnancy, but it was set in stone at the moment of conception because it’s determined by their genes

    It’s the sperm that has the deciding vote on your baby’s sex. That’s because eggs always have XX chromosomes, while sperm has XY chromosomes. If the sperm contributes an X chromosome, the resulting embryo will have XX chromosomes and be female. However, if the sperm contributes a Y chromosome, the embryo will have XY chromosomes and be male.

    Take a quiz

    Find out what you can do with our Health Assistant

    Signs and symptoms you’re having a boy or a girl 

    There are many old wives’ tales that claim to predict the sex of your baby. As exciting as they may sound, sadly, most of them aren’t backed by any scientific evidence. So, let’s myth-bust some of the most common “signs” of whether you’re having a boy or a girl. 

    Early scans 

    Some people believe you can predict your baby’s sex by looking for certain signs on early ultrasound scans — sometimes as early as 12 weeks. These include:

    Nub theory 

    The “nub theory” involves examining the genital tubercle, which is the “nub” that will eventually develop into male or female genitalia. The nub looks the same in all fetuses before 15 weeks, but according to nub theory, the angle of the nub can supposedly determine the sex of the baby.

    Ramzi theory 

    According to the Ramzi theory, which was created by Dr. Saad Ramzi Ismail, the placement of your placenta in your uterus can predict the sex of your baby. If your placenta is forming on the right side, you’re having a boy, and if it’s developing on the left side, you’re having a girl. Experts don’t consider the Ramzi method to be a reliable way of predicting your baby’s sex. 


    Some people believe that a baby’s sex can be determined by their heart rate. Specifically, a fetal heart rate below 140 beats per minute indicates a boy, while a rate over 140 suggests a girl. However, research has shown that this isn’t accurate. 

    Skull shape

    The “skull theory” involves looking at earlier ultrasound images to predict the baby’s sex based on the shape and size of its skull. While some people swear by this method, others see it as a fun old wives’ tale with no scientific backing. 

    Baby bump 

    Many people think that the shape of your bump during pregnancy can predict if you’re having a boy or a girl. A low bump supposedly means it’s a boy, while a high bump means it’s a girl. However, this isn’t true, and there isn’t any scientific evidence to support this theory.

    Breast size

    A few small studies have suggested that your breast size may indicate whether you’re having a boy or a girl. Your boobs grow and change a lot during pregnancy, but health care providers don’t recognize this as a way to establish the sex of your baby. 

    Nipple color

    Speaking of breasts, an old wives’ tale claims that darker nipples are one of the many signs you’re having a boy. In reality, your nipples darken due to pregnancy hormones — regardless of whether you’re having a boy or a girl. 

    Linea nigra

    Another common pregnancy myth is that your linea nigra — that dark line down the middle of your belly — can be one of the many signs of having a girl or boy. Your linea nigra appears as your hormone levels rise. If your linea nigra runs from your belly button downward, you’re having a girl. If it runs from the belly button up to the ribs, it’s a boy.

    Blood pressure

    A small study suggested that your blood pressure before conception could indicate whether you’re more likely to have a boy or girl. Unsurprisingly, this is just a myth, and doctors don’t use it to establish the sex of a baby. 

    Urine color

    Have you heard the myth that the color of your pee can indicate the sex of your baby? The truth is there’s no correlation between the color of your pee and the sex of your baby. The color, smell, and volume of pee can change throughout the day due to various factors, such as what you eat and drink, if you have an infection, and any vitamins or medications you’re currently taking. 


    Pregnancy is a time of major changes, so it’s little surprise if you feel more stressed than usual. A small study suggested that if you were stressed when you conceived, you may have a higher chance of having a girl. This is just a myth, but keeping stress levels low during pregnancy is a good idea anyway!


    Forgetfulness is normal and very common during pregnancy, so much so that the phenomenon has been dubbed “pregnancy brain.” One study showed that women who gave birth to girls performed worse in memory tests than those carrying boys. The study only involved 39 women, though — so you can probably chalk the results up to coincidence. 

    Mood swings

    Some people think that the estrogen produced by a female fetus can affect the mother’s temperament, causing mood swings. However, anyone who is pregnant can experience mood swings due to hormonal fluctuations, so these mood changes aren’t related to the baby’s sex.

    Pregnancy or morning sickness

    Another popular belief is that the hormones produced by a female fetus can cause more severe cases of pregnancy sickness. But is nausea in pregnancy a sign of a girl? In reality, the severity of nausea and vomiting varies from person to person, and even the same person can have different experiences during different pregnancies. 

    Food cravings and aversions

    Food cravings are one of the most common symptoms during pregnancy. A common myth is that a female fetus causes cravings for sweets, and a male fetus causes cravings for savory and salty foods. The truth is that as your hormones fluctuate during pregnancy, you may crave or avoid certain foods, and some people report craving foods due to their nutritional requirements.

    Hair and skin

    Have you heard the old wives’ tale that having a baby girl will make you lose your beauty? It’s not true — and probably not the best way to start your mother–daughter relationship! Pregnancy hormones can be unpredictable and affect everyone’s skin and hair differently

    Face shape

    If your face becomes rounder and fuller during pregnancy, the baby is believed to be a girl — or so the theory goes. It’s unclear where this myth originated from, but there’s no real evidence to suggest the shape of your face can determine the sex of your baby.

    Body temperature

    Changes in your body temperature are most likely due to normal hormonal fluctuations in pregnancy and not a sign of your baby’s sex. It’s totally common to feel both overly hot and cold at different stages of pregnancy. 

    Ancient charts and calendars

    The Chinese gender calendar, or the Chinese birth chart method, has been around for over 700 years and involves calculating the lunar age of the mother and the lunar date of conception. Like ancient Chinese culture, the Mayans also had a method for predicting a baby’s sex. They used the mother’s age and month of conception to determine the sex of the child. Some people believe that these are reliable methods of figuring out if you’re having a boy or a girl, but there’s no scientific evidence to support their accuracy. There’s no harm in giving them a go, though. 

    Medical tests to learn your baby’s sex

    It’s no wonder so many people believe in these myths — they have an almost 50% chance of being right, after all! But if you’re looking for more reliable ways of finding out the sex of your baby, these are some of the scientifically proven tests that your health care provider can use:

    During your ultrasound scan, the ultrasound technician may use the “three lines method” (also known as the “hamburger sign”) to determine the sex of the baby. If they see three distinct lines in the genital area, it’s a sign that the baby is female. These lines represent the labia majora, the clitoris, and the labia minora.


    Do you feel more tired when pregnant with a boy?

    There’s no evidence that tiredness means you’re pregnant with a boy. Fatigue is a common symptom of pregnancy and has nothing to do with the sex of your baby. Hormone changes play a big role in why you might be feeling more tired than usual — you’re growing a human inside you! It’s completely normal to feel sleepy. 

    Can the baby’s sex change after conception?

    Your baby’s sex is determined at the moment of conception when the sperm fertilizes the egg. This means that the sex of the baby cannot change during pregnancy. Both sexes start the same way in the uterus, and it takes a few weeks for a baby’s genitals to develop during pregnancy — but that doesn’t mean the baby’s sex changed.

    Does the mother’s age affect the baby’s gender?

    Your age certainly can impact your chances of conceiving, but there’s no real proof that age can determine whether you’re having a girl or a boy. Remember: chromosomes are what determine a baby’s sex.


    “20-Week Ultrasound (Anatomy Scan).” Cleveland Clinic, Accessed 5 Sep. 2023.

    Adkins-Regan, Elizabeth. “Hormonal Organization and Activation: Evolutionary Implications and Questions.” General and Comparative Endocrinology, vol. 176, no. 3, 1 May 2012, pp. 279–85, doi:10.1016/j.ygcen.2011.12.040.

    “Am I Pregnant?” Cleveland Clinic, Accessed 5 Sep. 2023. 

    “Ambiguous Genitalia.” Mayo Clinic, 18 Apr. 2018,

    Bethune, Michael, et al. “A Pictorial Guide for the Second Trimester Ultrasound.” Australasian Journal of Ultrasound in Medicine, vol. 16, no. 3, Aug. 2013, pp. 98–113, doi:10.1002/j.2205-0140.2013.tb00106.x.

    Bhide, Amar, and Ganesh Acharya. “Sex Differences in Fetal Heart Rate and Variability Assessed by Antenatal Computerized Cardiotocography.” Acta Obstetricia et Gynecologica Scandinavica, vol. 97, no. 12, Dec. 2018, pp. 1486–90,  doi:10.1111/aogs.13437.

    “Changes during Pregnancy.” The American College of Obstetricians and Gynecologists, Accessed 5 Sep. 2023.

    “Urine Changes.” Cleveland Clinic, Accessed 5 Sep. 2023.

    “Chromosome.” MedlinePlus, Accessed 5 Sep. 2023

    “Common Health Problems in Pregnancy.” NHS, Accessed 5 Sep. 2023.

    “First Trimester Fatigue.” University of Rochester Medical Center, Accessed 5 Sep. 2023.

    “FAQ: Cell-Free DNA Screening.” UCSF Health, Accessed 5 Sep. 2023.

    “Having a Baby after Age 35: How Aging Affects Fertility and Pregnancy.” The American College of Obstetricians and Gynecologists, Feb. 2023,

    Hill, A. J., et al. “Nutritional and Clinical Associations of Food Cravings in Pregnancy.” Journal of Human Nutrition and Dietetics, vol. 29, no. 3, June 2016, pp. 281–89, doi:10.1111/jhn.12333.

    “Hormones during Pregnancy.” Johns Hopkins Medicine, Accessed 5 Sep. 2023.

    Katz, Daniel, and Blair Wylie. “568: The Chinese Birth Calendar for Prediction of Gender - Fact or Fiction?” American Journal of Obstetrics and Gynecology, vol. 201, no. 6, Dec. 2009, p. S211,

    “Linea Nigra.” Cleveland Clinic, Accessed 5 Sep. 2023.

    “NIPT Test.” Cleveland Clinic, Accessed 5 Sep. 2023.

    “Non-Invasive Prenatal Testing (NIPT).” NHS Inform, 6 Mar. 2023,

    “Boy or Girl? It’s in the Father’s Genes.” Newcastle University, 11 Aug. 2015,

    Retnakaran, Ravi, et al. “Maternal Blood Pressure Before Pregnancy and Sex of the Baby: A Prospective Preconception Cohort Study.” American Journal of Hypertension, vol. 30, no. 4, Apr. 2017, pp. 382–88,

    Sharp, K., et al. “Memory Loss during Pregnancy.” British Journal of Obstetrics and Gynaecology, vol. 100, no. 3, Mar. 1993, pp. 209–15,

    Skin Conditions during Pregnancy.” The American College of Obstetricians and Gynecologists, July 2022,

    “Symptoms of Pregnancy: What Happens First.” Mayo Clinic, 3 Dec. 2021,

    Vanston, Claire M., and Neil V. Watson. “Selective and Persistent Effect of Foetal Sex on Cognition in Pregnant Women.” Neuroreport, vol. 16, no. 7, 12 May 2005, pp. 779–82, doi: 10.1097/00001756-200505120-00024.

    “Vomiting and Morning Sickness.” NHS, Accessed 5 Sep. 2023. 

    Walsh, Kate, et al. “Maternal Prenatal Stress Phenotypes Associate with Fetal Neurodevelopment and Birth Outcomes.” Proceedings of the National Academy of Sciences of the United States of America, vol. 116, no. 48, Nov. 2019, pp. 23996–4005, doi: 10.1073/pnas.1905890116.

    “Why Do I Feel Cold in Pregnancy?” Tommy’s, Accessed 5 Sep. 2023.

    “X Chromosome.” MedlinePlus, Accessed 5 Sep. 2023.

    “Y Chromosome Infographic.” National Human Genome Research Institute, Accessed 5 Sep. 2023. 

    Żelaźniewicz, Agnieszka, and Bogusław Pawłowski. “Breast Size and Asymmetry during Pregnancy in Dependence of a Fetus’s Sex.” American Journal of Human Biology, vol. 27, no. 5, Mar. 2015, pp. 690–96, doi: 10.1002/ajhb.22716.

    History of updates

    Current version (26 September 2023)

    Medically reviewed by Dr. Angela Jones, Obstetrician and gynecologist, attending physician, Jersey Shore University Medical Center, New Jersey, US
    Written by Olivia Cassano

    Published (02 January 2019)

    In this article