How soon can fetal sex be determined?
March 30, 2011 1:31 AM   Subscribe

How early in a pregnancy can fetal sex be determined?

Wikipedia has a surprisingly small amount of information on this (at least, that I could find). I'm interested in not only (1) what is common practice (when do people generally learn their baby's sex), but also (2) what is technically feasible (on the cutting edge of modern science, what is the earliest that it is possible to find out, and are such methods actually in use anywhere).

Most relevant out of all this would be information about (3) the middle ground (between 1 and 2 above) of what procedures are typically available if you want to find out fetal sex early, and what are the costs/risks associated with such procedures.

A related concern is (4) how much this kind of effort to find out could encounter resistance (either due to questions of legality or just a hesitancy to perform such procedure(s) on the part of the medical providers -- or for that matter insurers). (Sometimes resistance comes in the due to the use of new, potentially unsafe technologies; sometimes it comes out of fear of encouraging sex-selective abortion.)

Lastly, (5) which countries or states are more advanced technologically, or more permissive legally, with regard to the relevant procedure(s)? In other words, if you're pregnant and want to find out your baby's sex soon, where's the best place to be?
posted by jef to Health & Fitness (15 answers total) 2 users marked this as a favorite

At 10-12 weeks, if a mother undergoes chorionic villi sampling (CVS), and entire genetic workup of the fetus can be done. The process is essentially a placental biopsy. The risks included bleeding,miscarriage, etc. They're well published. If the sample is good, the accuracy is very high.

CVS is typically used for determining if the fetus has Trisomy-21 (Down syndrome) or other genetic disorders.

Since it is a genetic test, gender falls out of that, but that is not its primary use, so I imagine you would have a lot of push back if you requested this test specifically for gender, especially because of the risk of miscarriage.

Even if you could argue family risk (T21 in the family, already had a child with T21, maternal age, etc), you couldn't get a doctor to run it much earlier because the risk of miscarriage goes up, and I personally wouldn't recommend this test at its prescribed date unless there was another known risk of genetic abnormality.

There are no doubt, other tests/scans that are far less invasive, but these are typically probability tests and won't necessarily be accurate (this includes ultrasound).

As a kid, I grew up at a time when a baby's gender wasn't known until show time, unless something horrible was going on that required an amnio.

Therefore, I have two questions (1) what's your hurry? and (2) if you are in a social/familial position where this matters so much, wouldn't it make more sense to ask how to change that?
posted by plinth at 3:49 AM on March 30, 2011

With ultrasound, sonographers/ultrasound technicians can make a guess starting around 15-16 weeks, if the baby is in the right position. Your mileage will vary with willingness of providers to book a non-medically indicated 15-16 week scan, and it will vary again with willingness of individual sonographers to make gender guesses at that stage.

I'm not a sonographer, but I do work with them. I know some who will guess for patients who book 15-16 week scans just for gender, and some who will not. Sonographers tend to be much more willing to reveal their guesses at the routine 18-20 week fetal anomaly scan--only 2-3 weeks later--when they can be a little bit more accurate (but still a guess).

If this isn't a hypothetical, and you're setting out to determine fetal sex as early as possible in a real pregnancy, I suspect that everyone you encounter in this pursuit is going to be wondering "what's your hurry?"
posted by equivocator at 4:08 AM on March 30, 2011

If you do IVF, they can determine the embryo's sex before it is even transferred into the womb, I believe. The practical uses for this are when parents are carriers for a disease that only affects one sex and not the other. I think people have questioned whether this should be allowed or not. Googling should turn up something.
posted by lollusc at 4:29 AM on March 30, 2011 [1 favorite]

In the U.S., it is usually determined at the 20 week ultrasound if the baby is in the right position. I was in a different country for my pregnancy and had an ultrasound at ~14 or 15 weeks that they determined the sex.
posted by k8t at 5:41 AM on March 30, 2011

There's an ultrasound that many people do at around 13 weeks which is called an NT scan; it's used to better asses the risks for Downs and a few other things and help people decide whether to undergo the more invasive CVS or amnio. Anyways, apparently sometimes the ultrasound techs will give a gender guess then; the genitalia aren't so well developed yet, but there's some theory about the "angle of the dangle". No idea if these guesses are accurate, just have heard what women have been told.
posted by wyzewoman at 5:56 AM on March 30, 2011

In the US, it can be guessed as early as 14 weeks from an ultrasound, but most won't commit either way at that point since it's still too early.

Definitely by the 18 - 20 week anatomy scan it can be determined, if the baby is being cooperative that is.

(My cousin is about to have her second any day now, and the ultrasound tech took a guess at 14 weeks. Her doctor was upset at the tech for doing so as my cousin had her heart set on a particular sex, but there was a substantial chance the tech could have been wrong or the baby wasn't developed enough to see clearly.)
posted by zizzle at 6:33 AM on March 30, 2011

In response to question #4, no ethical healthcare provider is going to do a CVS (which is invasive and carries the risk of miscarriage) solely to find out the sex. So unless you're already having that done for other reasons, you need to wait until 18-20 weeks when the sex is clearly determinable by ultrasound.

I will say that at 12 weeks I was able to see what looked an awful lot like male genitalia on my ultrasound, but it could have been a still-developing clitoris and labia, so I didn't make any firm predictions. I was right, though!
posted by tetralix at 7:51 AM on March 30, 2011

I had a CVS done due to "Advanced Maternal Age." (snort)

There were some scheduling issues as my OB did not want to schedule the CVS too early, so even though the clinic was willing to have me in at 10 weeks, she didn't want me going in until closer to 12. It was then two weeks until we got the results. So we found out at 14 weeks.

At the clinic, the ultrasound technician said "well, it's a little early to tell for certain, but if I had to guess...Do you want to know? If I had to guess, I'd say you are having a girl."

She was wrong.
posted by ambrosia at 8:07 AM on March 30, 2011

A small amount (maybe 5%) of the free floating circulating DNA in maternal blood is derived from the fetus. This DNA is thought to derive from dying cells which dump their contents into circulation and the fetal portion is probably placental in origin. One of the most cutting edge methods of determining the sex of the fetus is to look for circulating fetal DNA present in maternal blood and then amplify and sequence it to determine the sex. Analyzing fetal DNA in maternal blood is currently a hot field of research.

There is a company that claims to be able to determine the sex as soon as 5 weeks after conception based on some variation of this concept. In about 5 years when sequencing costs drop sufficiently expect this procedure to become routine. Other companies are pursuing similar approaches but wait until 10 weeks instead of 5.
posted by euphorb at 8:36 AM on March 30, 2011 [1 favorite]

If you really need to know, I would get a genetic test, and not rely on ultrasound. Six scans, done in every trimester and by seven different techs all told me I was having a girl... you can guess how this ends. My son was born in June 2009, so it wasn't an "antiquated equipment" issue.
posted by Leta at 9:20 AM on March 30, 2011

We went for a second nuchal translunsancy test ( long crappy story) and found out that our boy was a boy at 11 weeks. It was pretty obvious and they were right. Now at almost 4, he is demanding his "wunch" I need to go mother but best of luck to you!!!
posted by pearlybob at 9:51 AM on March 30, 2011

We found out we were having a boy when we had the ultrasound accompanying our amniocentesis at 15 weeks -- results of amnio confirmed boy a week later. Most people find out when they have the anatomy survey ultrasound at around 20 weeks unless there's a reason to have CVS or amnio earlier.
posted by rabbitrabbit at 11:05 AM on March 30, 2011

Just wondering on these ultrasounds: it sounds like it's more likely to be a girl mistaken for a guy rather than the other way around, correct?
posted by jenfullmoon at 1:24 PM on March 30, 2011

To my knowledge, it is the opposite - a boy is more likely to be mistaken for a girl. The US tech is looking for a penis. If they see a penis, they know it's a boy. If they don't see a penis, it's always possible that they just didn't see it, and it's a boy who is being bashful or squirmy. Said organ is about the size of a grain of rice at the time of early ultrasounds, so it's possible to miss it.
posted by bq at 4:07 PM on March 30, 2011

lollusc: "If you do IVF, they can determine the embryo's sex before it is even transferred into the womb, I believe."

There is a clinic in Chicago which will sort the sperm out between male and female. I can't find it now but I'm pretty sure I read in the past that their success rate is 70% for a girl and slightly lower for a boy.
posted by IndigoRain at 6:39 PM on March 30, 2011

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