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I have seen varying opinions from 12 weeks to 20 weeks. At what point in the gestation will the Doctor be able to ascertain the sex of the child, assuming there are no developmental complications.

EDIT Question was previously related to Gender, I modified the question to reflect my intent.

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    Considering my 6 year-old nephew was thought to be a girl until the actual birth, I'd say 40 weeks :-)
    – Karl Bielefeldt
    Aug 13, 2014 at 19:33
  • Calvin is right...you should change your question to "When will I know the baby's sex?", as that is a far more purely biological question.
    – swbarnes2
    Aug 13, 2014 at 20:02
  • I should of used sex instead, I have amended the question.
    – Creamstout83
    Aug 13, 2014 at 21:24
  • It depends. We got the regular ultrasound on daughter number one, and it was a fuzzy mess. My wife was older with number two, so we had a "diagnostic ultrasound" as an alternative to amniocentesis to check for downs or other genetic issues. With that ultrasound, we could see the folds in the surface of the brain, the nasal passages, the heart, all four chambers and the valves in action. I don't see how the technician could not know gender at 12 weeks if you had that procedure.
    – Marc
    Aug 14, 2014 at 20:19
  • In the UK we are told at our 20 week scan if possible (i.e. baby is in the right position to see).
    – LauraJ
    Jan 28, 2015 at 15:15

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While Calvin's answer is awesome, you may be able to identify the baby's genitalia at an ultra sound.

In the US, OB/GYNs don't usually do ultra sounds between 12 and 20 weeks, and in most cases the genitalia will not be seen at 12 weeks.

At 20 weeks you will be able to see it in most babies, however, some babies are in a position where you cannot see it. Depending on doctor they may not want to spend too long time finding out about it - I believe at 20 weeks you also look for 4 chambers of the heart, kidneys and 2 brain halves, things like that.

In some cases, the doctor (or, in fact, ultra sound technician) think they saw the genitalia, but it was interpreted wrong. You don't know for sure until the baby is born.

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  • Thanks for the tips on what to look for in the ultrasound, my father had a genetic heart defect so I'll be paying close attention to the more important body parts during our ultrasounds.
    – Creamstout83
    Aug 13, 2014 at 21:26
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    Note that if your father had a genetic heart defect, you certainly should mention it to your obstetrician or nurse/midwife, and may want to have a more advanced cardiac focused ultrasound with a neonatal cardiologist. My oldest had a murmur during his 32 week checkup, which led to the same- turned out to be a harmless valve defect, but they were quite thorough and should be for you as well. Many heart defects can be detected before birth or shortly after, and can be lifesaving to detect it then.
    – Joe
    Aug 13, 2014 at 22:03
  • @Creamstout83 I am not actually 100% certain when they look for what - I just recall they are able to see more and more details in the organs. And as Joe said, if something seems abnormal, they might send you to a specialist center with more fancy equipment.
    – Ida
    Aug 13, 2014 at 23:36
  • The 20 week ultrasound likely wouldn't find cardiac defects; it's just looking that it's there, mostly. The cardiac echo is able to see blood flow direction (or something to that effect), so you can see whether blood is properly leaving one chamber and entering another without leakage. In our case it was purely coincidental that they noticed - the nurse/midwife heard a skip in the heartbeat during the normal check, so sent us for a more thorough check, which identified this - which is unrelated entirely to the maybe skipped heartbeat (or maybe just misheard).
    – Joe
    Aug 14, 2014 at 22:09
  • When I was born, my mother quickly realized they were wrong with their prediction and said, literally "That's gonna fall off, right?" - sorry mom, it didn't. But I totally had girl clothes for the first 3-6 months because that's what they were told I was going to be.
    – corsiKa
    Aug 28, 2014 at 15:40
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EDIT: The original question has been edited from being about gender to being about sex (as many comments and this answer reference). While my answer is no longer relevant, I believe it is fair to preserve it here for purposes of incidental education

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Well, in general, gender identity tends to coalesce toward the end of puberty. While many individuals have an idea what gender they will identify with before then, many, especially those raised in conservative households, will have to pass through puberty and sometimes even live away from home for a while before coming to terms with their own gender identity. This isn't really something a doctor can tell with any reasonable degree of granularity, as neuroscience has not yet developed any accurate methods of determining gender, but this should be an ongoing dialogue with your child through upbringing. In some ways, there will never really be any absolute certainty in gender identity, but I would expect within the first few years away from home it will be unlikely to be further refined, especially as our society becomes more accepting of non-cis-identifying individuals.

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  • note that in some cases, non-cis people tend to start questioning their birth-assigned gender as early as toddlerhood.
    – Ida
    Aug 13, 2014 at 20:29
  • Absolutely. Some fortunate individuals will even be able to prevent an undesired puberty if they live in a loving and accepting home and are made aware of these issues early on in life, either through education or personal conviction.
    – Calvin
    Aug 13, 2014 at 20:46
  • Thanks for your response, I have amended the question to reference the child's sex not gender.
    – Creamstout83
    Aug 13, 2014 at 21:25
  • Thank you for your question, I believe it served as an unexpectedly educationally experience for all of us.
    – Calvin
    Aug 13, 2014 at 21:28
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You can do a prenatal DNA test at 10 weeks that will determine the sex of the baby. My wife and I did this and it costs us $150 in the U.S., although our OB-GYN said that this test will soon become part of the standard of care since it also identifies genetic defects. So I would assume most insurances would cover it when that happens and the price would come down even further.

They just draw some of the mother's blood, and then sequence the baby's DNA out of it. Fascinating :)

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