Can you find out the gender at 12 weeks?

What’s formed by 12 weeks, and what a scan can see

Weeks here count from the first day of your last period. Twelve weeks into pregnancy is 10 weeks after conception. By then, Mayo Clinic says, your baby might be about 2 1/2 inches (61 millimeters) long from crown to rump. Fingernails are sprouting, and the face has “a more developed profile” (Mayo Clinic).

The outer genitals are still taking shape. Mayo Clinic says they “start developing” by the end of week 11. Cleveland Clinic says they begin to form around week 10, when “it’s too soon to see them on an ultrasound,” and are “fully developed” at week 14. At the end of week 12, it adds, the sex “won’t be visible on ultrasound for several more weeks” (Cleveland Clinic). A 12-week call rests instead on which way a small bump points.

Why boys and girls look alike at first

Every baby starts out with the same parts. Between the legs sits a small bump, the genital tubercle, which the StatPearls medical reference calls “the primordium of the future developing clitoris or penis”: the early form of either one. These early stages are identical in boys and girls “until around the 9th week post-fertilization,” about 11 weeks of pregnancy (StatPearls).

In a boy, a hormone called DHT makes the bump grow longer to form the penis, and folds beside it join to form the scrotum. In a girl, the bump becomes the clitoris, and StatPearls dates the start of a girl’s changes to 11 weeks after fertilization, about 13 weeks of pregnancy. By that timeline, at 12 weeks a boy’s changes are under way and a girl’s haven’t begun. It’s one reason a young boy can pass for a girl on an early scan.

How a 12-week call is made

What a scan shows is the baby’s sex, read from the anatomy. In the late first trimester and early second, a 2009 review says, the call rests mainly on which way the genital tubercle points: down for a girl, up for a boy. By the late second trimester, it rests on a direct look at the genitals (Odeh and colleagues, 2009).

Judging the direction takes a true side view down the middle of the baby, and in boys the angle grows as the baby grows (Efrat and colleagues, 1999). Online, this bump is called the “nub.” Nub theory: how it works and how accurate it is explains the method and why a screenshot can mislead. Skull shape is another guess; see skull theory.

Will they tell you the sex at the 12-week scan?

The routine scans around 12 weeks are medical scans with other jobs to do. Whether anyone looks for the sex depends on the country, the hospital and the sonographer.

In the U.S.: the NT scan

Your doctor or midwife may suggest a nuchal translucency (NT) test, usually done between the 11th and 14th week of pregnancy. This medical ultrasound measures the thickness of an area at the back of the baby’s neck, and a blood test is done too, to screen for Down syndrome. More fluid than normal there means a higher risk for Down syndrome, but “it does not tell for certain” that a baby has it (MedlinePlus).

Finding the sex isn’t what the NT scan is for. The U.S. practice guideline for pregnancy scans lists the external genitalia among the checks for second- and third-trimester scans, “If medically indicated or the patient wants to know” (ACR–ACOG–AIUM–SMFM–SRU). Want a guess? Ask at the start, and ask how sure they are.

In England: the 12-week dating scan

The NHS offers a medical scan “at around 10 to 14 weeks of pregnancy,” called the dating scan or 12-week scan. “It’s used to see how far along in your pregnancy you are and check your baby’s development,” and whether you’re expecting more than 1 baby. It can also be part of the combined test, which screens for Down’s syndrome by pairing a blood test with the NT measurement (NHS).

The sex isn’t part of it. “Finding out the sex of your baby is not offered as part of the national screening programme,” the NHS says. It points to the 20-week scan instead, where finding out “depends on the policy of your hospital” (NHS). Hospitals’ own leaflets differ. Gateshead Health says: “It is not possible to determine your baby’s sex at the Dating Scan, the baby is too small at this stage” (Gateshead Health). Gloucestershire Hospitals will only “try to give you an opinion” if asked, and says you can usually find out at the anomaly scan at around 20 weeks (Gloucestershire Hospitals).

Check your scan date, too. A “12-week scan” can fall anywhere from about 10 to 14 weeks, so yours may come before 12 weeks, when the guidance below discourages a call.

What sonographers’ guidance says

The Australasian Sonographers Association (ASA) says in a 2022 position statement that sonographers “are under no obligation to provide sex determination in first trimester ultrasounds for social reasons.” A sonographer may give one at their discretion, once you’ve confirmed out loud that you’ve been told about “the potential inaccuracy at this early stage” (ASA, 2022).

What the studies found at 12 weeks

These three studies give separate results for 12 weeks. All were hospital-based, and none can say how sure any one scan will be.

• London, 1999: 524 women at 11 to 14 weeks. An unselected group at a university obstetrics department, scanned over the belly, or internally when needed, and judged in side and cross-section views, with the sex checked at birth. At 12 weeks, 87% of babies got a call, and counting every baby scanned, 75% got a correct one; at 14 weeks, 98% and 90%. The abstract doesn’t give the number scanned each week (Whitlow and colleagues).
• Israel, 2006: 656 pregnancies at 12 to 14 weeks. Babies were scanned over the belly at a hospital in Petah Tikva and judged by the bump’s angle, with ages set by length. A call was possible for 85% of babies at 12 weeks to 12 weeks 3 days, and 96% at 12+4 to 12+6. Checked in 555 newborns, “boy” calls were right 99% to 100% of the time at every age. “Girl” calls were right 91.5% of the time at 12 to 12+3, and 99% at 12+4 to 12+6 (Efrat and colleagues, 2006).
• London, 1999: 172 pregnancies at 11 to 14 weeks, at a fetal medicine center, scanned right before chorionic villus sampling, a test of the baby’s chromosomes. The rule: tilted up more than 30 degrees from a line along the lower back meant a boy, and anything less, a girl. Accuracy was 70.3% at 11 weeks and 98.7% at 12, and the abstract doesn’t say whether any baby went without a call. At 11 weeks, 56% of boys were called girls; at 12, 3%. The abstract doesn’t give the number scanned each week, and a fetal medicine center’s results can’t tell you how sure a 12-week call elsewhere will be (Efrat and colleagues, 1999).

The three used different methods and counted in different ways, so their figures can’t be merged into one “12-week accuracy.” How accurate is a gender ultrasound at 13, 14, 15 and 16 weeks? has more, week by week.

Why waiting a week or more pays off

In all three studies, results improved as the weeks passed: more babies got a call, more calls were right, or both. In Israel, they improved even within week 12.

At 14 weeks, Mayo Clinic says, “Your baby’s sex likely will become clearer this week” (Mayo Clinic).

Your dates matter too. In the larger London study and the Israeli one, the week was confirmed by the baby’s length on the scan, not by a calendar. At England’s medical dating scan, the NHS says, your due date “may be adjusted according to the ultrasound measurements.” So 12 weeks by your calendar may not be 12 weeks by your baby’s size. How far along am I? explains why dates move.

Why careful sonographers hold back

The ASA and a 2009 review both draw the line at 12 weeks. The review says: “An attempt to determine the fetal sex should not be made before 12-weeks’ gestation because this early, it is relatively inaccurate.” The ASA says, “Sex determination by ultrasound prior to 12 weeks should be discouraged,” and says there “can be significant error in sex determination that varies across 11-14 weeks gestation age.”

An Australian study agreed. Seven sonographers at a specialist private obstetric practice in the Illawarra, New South Wales, scanned 640 babies across all three trimesters and predicted the sex where they could, judging first-trimester scans from the side. Under 12 weeks, the “overall success rate” was 54%; the abstract doesn’t say how many babies that covers, or whether those with no call count. “Predictions prior to 12 weeks should be discouraged,” the authors wrote (Kearin and colleagues, 2014).

None of this makes a 12-week call sure. The ASA asks sonographers to “state that errors exist with early predictions,” and to explain that the sex can be assessed “with more accuracy at a later gestational age.”

Want to know sooner? Ask about the blood test

Cell-free DNA screening (NIPT) is a blood test your doctor or midwife orders to screen for chromosomal conditions, and it “can be done as early as 10 weeks of pregnancy.” It can also tell whether XX or XY chromosomes are present, a result Cleveland Clinic calls “highly accurate, but not 100% accurate” (Cleveland Clinic). Tell your doctor or midwife whether you want to know the sex from it. The ASA counts NIPT among the tests that are more accurate for the sex than a first-trimester scan. In England, the NHS version “does not screen for other conditions or fetal sex” (NHS England). When can you find out your baby’s gender? lays out every option, blood test or ultrasound compares the two, and at-home gender blood tests covers the kits you take yourself.

Told “boy” or “girl” at 12 weeks? What to do next

A 12-week call can be right, but treat it as a first guess until a later look agrees.

• Ask how sure they were, and what they saw. “90% sure it’s a girl”: what a sonographer’s confidence means explains a hedged call, and Can an ultrasound be wrong about the gender? walks through why calls go wrong.
• Keep receipts. Buy neutral basics, and hold off on paint, engraving or anything you can’t return.
• Get a later look. The medical anatomy scan, at about 18 to 22 weeks in the U.S., is one chance: in most cases the sex can be seen then, depending on your baby’s position (Cleveland Clinic). Tell the sonographer at the start if you want to know. In England, it depends on your hospital’s policy.
• If a blood test said otherwise, tell your doctor or midwife. There are several possible explanations, a few of them medical, and only they can look into it (Dhamankar and colleagues, 2020). Ask whether genetic counseling is available. A keepsake scan can’t settle it.
• Hold the reveal until a later look agrees, so you only plan it once.

Twelve weeks and counting? Give the planner your due date to see which of our sessions are ready for you now and when the next one opens. Your entries stay on your device.

Why our studio books from 13 weeks, not 12

Could we tell at 12 weeks? Sometimes, but rarely with confidence, so we book from 13 weeks. Our Gender Confirmation, in Glendale, Los Angeles County, is a 2D scan, “the classic black-and-white picture.” If you can wait until 15, do: we’re more confident, and a second look is less likely.

Our promise: “If we can’t tell with confidence, we don’t guess.” When we can’t be sure, we say so, and you come back for a free re-check. No ultrasound can promise 100%. Planning a reveal? Tell us it’s a secret before you lie down. The screens stay off, we find the answer, and it goes into an envelope nobody can see through. The envelope is subject to availability, so ask for it when you book.

It’s a keepsake, not a medical exam: it doesn’t replace the anatomy scan or any appointment with your doctor or midwife, and it doesn’t check your baby’s anatomy or health. The FDA and the AIUM discourage ultrasound done only for a keepsake (FDA, AIUM), and Safety, in plain words quotes them. We book from 13 weeks, and we’re surest from 15: find out with us, check what you’ve been told or see prices.

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