According to a study conducted by Ined (National Institute for Demographic Studies), 9 out of 10 couples want to know the sex of their unborn baby, in particular to choose a name and better prepare for their arrival. Speaking of which, have you ever heard of the genital tubercle? A name that evokes an entire concept around birth, growth… and the child's sex. Yes, today we are talking about the very first prenatal ultrasound, the one where the guesses begin! So, girl or boy? It all starts with a tubercle.
CONTENTS:
- The First Trimester Ultrasound, THE Much-Awaited Moment
- The Genital Tubercle: What Is It?
- The Genital Tubercle Method for Guessing Baby's Sex
- The Morphology Ultrasound, a Confirmation
The First Trimester Ultrasound, THE Much-Awaited Moment
Scheduled at around 12 weeks of pregnancy, the first trimester ultrasound—also called the dating ultrasound—is often the first meeting with your baby. While your belly is just starting to round, and perhaps before you’ve even shared the good news with those around you, parenthood becomes a tangible reality. For the first time, you see your little one move. For the very first time, you hear the heartbeat. And for the umpteenth time, you find yourself wondering:
- “Is it a girl or a boy?”
But beyond this key question, the first ultrasound is primarily to reassure you about the progress of your pregnancy. Thanks to medical imaging, the sonographer checks for the presence of the gestational sac in the uterus, and the embryo itself. If there’s no embryo, it’s called an anembryonic pregnancy; if there’s no fetal heartbeat, it’s a missed miscarriage; and if there is more than one fetus, it’s a twin pregnancy. All of this information is examined one by one to ensure the viability of your pregnancy.
This is also when you get an exact date for the start of your pregnancy and, therefore, your estimated due date (EDD)!
Your doctor or midwife will then closely examine your baby and measure the crown-rump length (from head to rump), among others. Nuchal translucency is also assessed to estimate the risk of Down syndrome (trisomy 21). If the fetus shows a slight separation between the skin at the nape of the neck and spine, a space above the norm can indicate a higher risk of trisomy 21. This risk also increases with the mother's age and family history.
Finally, if you want to know your child's sex and only at your request, your midwife or doctor may mention your baby’s genital tubercle.
The Genital Tubercle: What Is It?
To define the genital tubercle (or genital bud), it is a precursor to the penis in boys or a precursor to the clitoris in girls.
Determined as soon as the egg is fertilized by sperm—two X chromosomes make a girl, one X and one Y chromosome make a boy—the sex of your child only starts to physically develop around the 5th week of pregnancy (WP) or the 7th week of amenorrhea (WA). Then, you have to wait around 9 WA to actually see any real difference between girl and boy.
At 12 WA, at the time of your first ultrasound, if you’re expecting a boy, his penis begins to take shape while his testicles are already producing testosterone. If you're expecting a girl, her uterovaginal canal, ovaries, and fallopian tubes develop in her body.
It is this difference, in the form of a tubercle, that allows a trained eye to make the early predictions.
The Genital Tubercle Method for Guessing Baby's Sex
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Use a clear image of your entire baby, taken horizontally, during the first ultrasound.
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Locate the genital tubercle, positioned at the lower belly, between the legs, and the spine.
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Compare the position of the tubercle to the spine, especially its angle. If they are fairly parallel to each other, you’re likely expecting a girl. If the tubercle points more upward, it’s most probably a boy.
However, if the image is blurry, if baby has their back turned, or if a hand moves at the moment of the photo, the guessing game is over! You’ll need to wait until the second trimester morphology ultrasound to find out more.
Before 22 WA, Interpretation Is Uncertain
Under optimal conditions—if the fetus is well positioned and the image is clear—interpreting the genital tubercle is a fairly reliable (but never certain) method to get a good idea of your baby's sex before birth.
That said, keep in mind that no technique is foolproof. Who hasn’t heard of a mom all ready for a little boy, who finally gives birth to a girl, or vice versa? While the baby’s sex is generally revealed with certainty during the second trimester ultrasound, some moms only get a definite answer once their newborn is in their arms.
The Morphology Ultrasound, a Confirmation
The morphology ultrasound is the second required exam during pregnancy. Done during the 5th month, between 21 and 24 WA, it is longer than the other ultrasounds and examines your baby's growth in much greater detail. At this point, your baby measures about 10 inches from head to toe and weighs about 1.1 lb (500 grams).
While the main objective of the dating ultrasound is to confirm proper implantation and fetal viability, the aim of the morphology ultrasound is to look for possible fetal abnormalities.
The healthcare professional takes cross-sectional images of the various organs: heart, brain, stomach, bladder, and intestines, as well as baby's arms and legs, to check that everything is developing well. Finally, your baby is measured from head to toe: biparietal and abdominal diameter, head and abdominal circumference, and femur length.
On the mother’s side, different aspects of the placenta are evaluated, the amount of amniotic fluid is checked, and so is the cervix.
Once all these steps are complete, your doctor or midwife will generally be able to tell you your baby’s sex.
Note: If you do not want to know your baby’s sex, make sure to say so—and keep reminding your medical team at each prenatal appointment. Indeed, as sonographers are used to expectant parents’ impatience, they might share the information very quickly!
Reveal Baby’s Sex or Not?
Genital tubercle, morphology ultrasound, in 3D or even sometimes extra scans—if you’re impatient, you might try everything to finally know whether a little boy or girl will join your family.
Other parents-to-be, after scouring their baby’s tubercle to no avail or after a second trimester ultrasound with an uncooperative baby, give up on knowing their child’s sex before birth to simply enjoy life’s surprises.
Sometimes, reassured by the genital tubercle clues, couples opt to wait until delivery day for confirmation.
Finally, out of superstition, strong belief, or because they already have children of each sex, many expectant mothers and fathers choose to keep the secret entirely. Regardless, remember that this deeply personal choice is only yours to make.
And What About Old Wives’ Tales?
The shape of your belly or your cravings are said to reveal much about the child you’re expecting. Indeed, there is no shortage of old wives’ tales trying to uncover nature’s greatest secret.
- Strong morning sickness would be associated with a girl. Maybe so! In October 2020, an American study showed that the birth of a girl results in a higher hCG hormone level. High hCG concentration is responsible for first trimester nausea.
- Regarding diet during pregnancy, craving sweet foods supposedly signals a girl, while preferring salty dishes means you’re expecting a boy. What do you think?
- The shape of your baby bump is also said to be a clue. High and pointy? It's a boy. Low and wider? It’s a girl. However, the shape of your belly also depends on the baby's position, your own body shape, and the number of previous pregnancies.
- Have you heard of the pendulum test? Just dangle a pendulum above your belly and watch its movement. Moves in circles? Girl. Swings back and forth? Boy.
- Grandmothers used to say that a baby girl steals her mother's beauty. Thus, a mother-to-be who is glowing is more likely to be expecting a boy, while a pregnant woman with a dull complexion and tired hair would be expecting a girl.
- The dark line that sometimes appears on pregnant bellies, called the linea nigra (Latin for "black line"), is said to reveal a girl—if it extends above the belly button. Otherwise, it's a boy.
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Have you tried one or more of these tricks? Have you tried to decipher your 12-week ultrasound using the tubercle method? Let us know if it worked for you!
*Ultrasound source: Imagerie médicale du Sud-Est lyonnais
