I had a lot, I believe 5 and then an in depth one to check my LO's heart. I only had so many because I have a congenital heart defect and they were screening her for that, and because when I would have been a few weeks pregnant (before a positive test) I had a CT scan (radiation and radioactive iodine) and was put on two medications known to cause birth defects.
Thank God my daughter was and is perfectly healthy
In Ireland pregnant women are covered under the mother & baby health scheme so most pre natal care is free, including doc visits, ultrasounds (not 3D though), hospital stay and post natal care till baby is 6 weeks old. You can pay to go private though or use your insurance if you have it. They only tend to do 2 ultrasounds unless there are health issues and concerns. I had one at 13 weeks but none again till 28 weeks. I thought that was all i was going to get but they scanned again at 32, 36 and 38 weeks. I kept asking why but they brushed me off saying stuff like: Ah it's quiet here today! Uh no, I was waiting nearly 3 hours in the clinic for one of my appointments! She kept flipping into breech position and back again but she was also posterior the whole time, they were waiting to see if she would turn around at all. This I found out later. My cousin on the other hand only got 2 scans, she went to 42 weeks and begged for another one to make sure everything was ok. They did but weren't happy about it. I agree though that u/s aren't a necessity as they can check baby's growth by palpating your stomach and they are expensive too. I only asked for my 28 weeks one coz they hadn't done an anotomy scan yet, the others they did themselves!
Usually two. One to see how far you are and one for anatomy. I paid for a gender one then had 3 from hospitals and doctors office so far but really only one is necessary unless there maybe a defect. Then you will neef a level II. I have had to have a level II and trust me. I rather only have one ultrasound than to sit a worry about the baby. Everything was fine but the 2 weeks of a wait was scary.
Ultrasounds are actually terrible for determining how big baby is. They can be off by a pound.