13 Weeks 6 Days Gender Reassignment

Kudos to people who can wait until the birth to find out if they are having a boy or girl. The feminist in me feels guilty about this, but I never wanted to wait that long. Pretty much the second I learned I was pregnant, I started trying to figure out if it was a boy or or girl.

The good news for people like me: ultrasounds can now detect a baby’s gender as early as 12-13 weeks gestation.

Genetic testing through CVS remains the most accurate way to determine fetal sex in the first trimester. But since this test carries a slight risk of miscarriage, many of us choose not to have it performed. (New blood-based tests that rely on cell free DNA can detect your baby’s gender as early as 9 weeks, without increasing the risk of miscarriage, but these are only about 95% accurate in the first trimester).

Until recently, forging genetic testing meant we had to wait until the second trimester screening to learn our baby genders, sometime around 18 to 20 weeks gestation. By that time, the penis, testes, and labial folds are clearly visible on an ultrasound.

The latest research, however, suggests we can learn the gender months earlier, during the ultrasound for the first trimester screen, which is performed sometime between 11 weeks 0 days to 13 weeks 6 days of gestation. The key is scheduling your scan towards the end that window.

Male and female fetuses look pretty similar throughout most of the first trimester. The genitalia are just starting to develop from their root, the “genital tubercle,” which slowly develops into either a penis or clitoris. This genital tubercle is same size in boys and girls until around 14 weeks gestation, when the penis begins to elongate.

A sonographer therefore has to rely on more subtle clues to determine gender in the first trimester. The angle of the genital tubercle is one important clue. By 12-13 weeks gestation, the angle of the penis begins to point up, towards the baby’s head, while the clitoris remains flat or points slightly down.

The ultrasound images below illustrate this. A male fetus is shown on the left, a female fetus on the right. The angle of the genital tubercle is noted with faint white lines.

From Efrat et al. 1999

In small study of 172 pregnancies, sonographers  were able to accurately detect fetal gender using this angle from about 12 weeks on. Before then, sonographers correctly identified only 70% of fetuses. They were most prone to misclassify the boys: roughly half of the male fetuses were misclassified as girls. So at 11 weeks, when the sonographers guessed that a fetus was a boy, they were usually correct. But when they guessed it was a girl, they were often wrong.

But by 12 weeks this method’s accuracy shot up to 98%. By 13 weeks, there were no more misidentifications; 100% of their classifications were correct. In a follow-up study of 656 pregnancies, sonographers were again perfectly accurate by 13 weeks.

At this point in pregnancy, using the angle of the genital tubercle is more accurate than trying to detect the labia or testes, the method commonly used to determine gender in the second trimester. Classification by the latter method was only about 75% accurate until 14 weeks.

(Incidentally, several websites, like this post at CafeMom and this one at About Health, claim that fetal gender can be detected with nearly 100% accuracy at the 6-8 week ultrasound using “Ramzi’s Method”. I tracked these claims down. All of them appear to derive a paper written by Dr. Saad Ramzi Ismail, which was posted to obgyn.net last year (and has since been removed). In it, Dr Ismail claims that the placenta is almost always on the left side for girls and on the right side for boys. While her paper is formatted and reads like a legitimate scientific article, it was never published in an actual scientific journal. Moreover, it seems extremely unlikely that, if we could determine gender by something as simple as the location of the placenta, we would already know this and use this method all the time. So, as far as I can tell, “Ramzi’s method” is pure junk science.)

The Bottom Line

If you want to learn your baby’s gender, schedule your first trimester scan for 13 weeks gestation. The methods used to detect gender at this fetal age are pretty new, so some sonographers may be hesitant to give your their best guess. But don’t let this deter you. Ask! They are very likely to get it right.

Additional Reading

Like this post? You may also like my take on fetal sex tests based on cell free DNA. With a simple blood draw, these tests can determine fetal sex as early as 9 weeks.


Efrat Z. Akinfenwa O.O, and Nicolaides K. H. (1999). First-trimester determination of fetal gender by     ultrasound. Ultrasound Obstet Gynecol 13:305–307.

Efrat Z., Perri T., Ramati E., Tugendreich D., and Meizner I. (2006). Fetal gender assignment by first-trimester ultrasound. Ultrasound Obstet Gynecol.27(6):619-21.

Emerson D.S., Felker R.E., and Brown DL. (1989). The sagittal sign. An early second trimester sonographic indicator of fetal gender. J Ultrasound Med. Jun;8(6):293-7.

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Congratulations, you’re pregnant! If you’re like me, one of the burning questions on your mind is whether you’re having a boy or a girl. No need to wait until that 20-week ultrasound; these 10 wives tales for determining the baby’s sex can predict whether to boy pink or blue!

I spent the morning with the WCCB Rising family making dessert hummus! I wish I could claim ownership to this awesome recipe, but there are so many different versions of it floating around the internet. However,the version I make can be found here. Or, watch Tera publicly acknowledge the growing baby bump live 

Ok, speaking of baby bump, after your encouragement (or calling me crazy- wink) for waiting to open the envelope yesterday, I am ready to rip into it! David and I have a special date planned for the weekend to finally find out whether our newest Baby D will be a he or a she!

I’ve been having a ridiculously good time consulting the old wives tales and for fun, thought I’d list them all out here then get you to weigh in… here we go!

1. Heart Rate. If the baby’s heart rate is above 140, it’s a girl. Below and it’s a boy.
This one confuses me because when should you take the measurement? Hailey was 129 at 7 weeks, 169 at 11 weeks, 144 at 15 weeks and 157 at 18 week. So far, baby’s heartbeat has been 165 at 10 weeks, 176 at 13 weeks and 138-141 at 15 weeks.

Predictor says: SPLIT boy/girl

2. How You Carry: If you are carrying big, round and high, it’s a girl. Low and all in front is a boy.
Well, I’m 5’1”. I carry wherever it can fit, so I feel like it’s all over. I feel my sides have expanded, so…

Predictor says: GIRL

3. Acne: If your skin gets worse, it’s a girl. If your skin is clear, it’s a boy.
My skin had been rough for me. I usually have clear skin, but I’ve had several big, deep zits show up and stick around. Ugh.

Predictor says: GIRL

4. Cravings: Sweet cravings means it’s a girl, salty cravings points to boy.
Olives, potato chips, soups… GIVE ME SALT.

Predictor says: BOY

5. Morning Sickness: If you’re sick as can be, it’s a girl. Feeling fine? It’s a boy.
It’s been more intense and lasting longer than it did with Hailey.

Predictor says: GIRL

6. Skin Test: Dry, rough skin means it’s a boy. Soft skin means it’s a girl.
…or could it just be winter? Either way, my skin is dry.

Predictor says: BOY

7. Chinese Gender Chart: Click here to go to Chinese gender calculator
This ‘method’ told me Hailey was a boy, FYI.

Predictor says: BOY

8. Leg Hair: If your leg hair grows faster, it’s a boy. If not, it’s a girl.
I haven’t noticed a big difference, but I’m in jeans all the time!

Predictor says: GIRL

9. Mood: If you’re moodier than usual, it’s a girl. If you’re chill, it’s a boy.
Oh man, have my emotions been all over the place this time! I can cry on cue.

Predictor says: GIRL

10. Mother’s Instinct
I feel like every real (ok, mythical) sign points to girl. However, my gut just tells me boy. It’s important to note that I was also convinced Hailey was a boy! I’m so ready to find out if my motherly instinct has failed me twice in a row or if I’ll be batting .500.

Predictor says: BOY

Unlike with Hailey, we WILL be sharing the baby’s sex with friends, family and of course, y’all! We will tell our families at Thanksgiving, then, if I can possibly wait that long, I’ll fill y’all in right after.

If you are as impatient as I am, I have a lot of friends say the Intelligender test was right for them!

Were gender myths or your gut feeling correct for you?

Please join in on my fun and tell me whether you think I’m having a boy or girl. And most fun of all, why?!

Have a great weekend!

Filed Under: Motherhood, PregnancyTagged With: first trimester, gender myths, pregnancy, pregnancy #2


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