I sent you a message with some suggestions but it seems like you need one for gender prediction so I would say you should go for it now!
I have never had one, but I was excited to learn that my dr. gives his patience one now sometime during one of the visits. I'm hoping ours will be within the next few months.
We had one at 22 weeks as hubby is away a bit, then off away from Oct till just before baby is born. We wanted to confirm that we were having a girl (undetermined at 20wk scan). So now we can decide on the name and decorte the nursery. Had some good pics, but our company said that if the scans weren't good, or if they couldn't confirm gender, we could come back. I'd say leave it till 26 weeks if you want the detailed facial pictures, but if you're like us and need to know quickly about the gender then the pics are still pretty fantastic. Hubby has a big nose, but looking at the pic, it looks like baby has my nose. Whoop!
Yes, we had one at our 21 week congenital scan. It was pretty amazing and very detailed. Our little bub, although the Dr said was a big baby (!), was all skin and bones at this stage still. She told us she'll do another one around week 28 (for fun) as the baby fattens up by this stage and will be a lot 'cuter'. Still fascinating to see though, so would definitely recommend it! PS we are leaving the sex a surprise, although it was sooo tempting to have a peak.
We had one at 19 weeks and it was neat but not amazing. My placenta is in the front of the uterus and the dr. had to work around it to try to get pictures. It was my first one and I never had them with my two previous pregnancies. I thought it was OK but not amazing. Good luck!