Hi

I dont know where you are so I m not sure if it will be correct for you...But At the start of my pg I went through a GP/OB, and he sent me for a dating scan (about 7-8 weeks) and then the 13 week scan for the downs test, etc...I loved having this one done, and in fact the only decent pic I have of my pg is the U/S from the 13 weeks scan, so Im glad I did it.
After about 12 weeks you can start going to the free antenatal clinic at the hospital and they arrange all the u/s's blood tests that need to be done for the rest of the pg, also see you for check-ups and do the urine/hr monitoring too.
I went for the 20 weeks scan which is an anatomy scan - to determine that all the legs and arms are there, that the kidneys are functioning and the arteries are where they should be!

I did the bloods and the Downs u/s (13 weeks) because I wanted t be prepared if something was wrong, but I know that lots of results are inaccurate with these tests, but for my piece of mind, I wanted to know so i guess it depends how you feel

Handy to know that you can request an u/s referral at ANY stage of your pg if you want one, although after about 32-36 weeks the baby is really too big for a clear pic of anything

HTH and hope you have a great pregnancy!!

Alexis