Why ultrasound at 20 weeks instead of later?

[janellesmommy]

I was wondering why the standard ultrasound is at 20 weeks. Wouldn't it be better to wait until much later, so that things are more developed and easier to see?

Would there be fewer misdiagnoses with a later ultrasound?

[ndakkitten]

It depends on the reason for the ultrasound. An ultrasound late in pregnancy can be VERY inaccurate with things like measurements, estimating due dates, etc. Once the baby starts getting "crowded" it makes it much harder to see certain things. Waiting a few weeks past 20 is fine however. Things like placental placement are better judged later in pregnancy. But for reasons like checking for developmental abnormalities, sooner is better.

To be honest, the reason most providers choose 20 weeks because that is the cut-off for termination in some states. Generally this stage is when the baby is developed enough for most congenital defects to be detected and the provider could offer the option to terminate if a condition incompatible with life is discovered. Most of them don't tell you this however.

[janellesmommy]

Originally Posted by ndakkitten

To be honest, the reason most providers choose 20 weeks because that is the cut-off for termination in some states.

Oh, that's interesting. I never thought of that.

[earthmama369]

I had a very early (dating) u/s with dd where we could see all of her but she was verrrry tiny. We had a few very late u/s with her as well, after a car accident. At ~34 weeks, we could see -- a leg, an arm, her back, her head -- all in different screenshots because she was far too big by that point to get all of her in one view.

With ds, I had one u/s at 17 weeks and that was just right. We could see all of him at once, get more accurate measurements, and easily check out his organs and bits.

[mwherbs]

very early ultrasound is the most accurate about dates only having an error factor of + or -3 days.
at 12 weeks limbs and other bits develop more and individual growth patterns develop to some degree
now at 20 weeks probably the last bit of time with some accuracy +2.1/-2.5 weeks not perfect on dating but what parents really want to know- sex of the baby can be seen- and it comes after the triple screening 16-18 weeks.

[shelbean91]

My ob that deliverd dd and ds1 liked to do u/s at 13 weeks b/c it was a good balance of accurate dating and making sure development was ok. That's what they told me anyway.

[JanetF]

To be honest, the reason most providers choose 20 weeks because that is the cut-off for termination in some states.

That's why it's done at that point in Australia too. The thing about "being reassured" by u/s is that there's not enough talk about who you'll feel or what your options are if the results aren't reassuring at all.