I have only ever had an ultrasound after miscarriage. Both times because of hemorrhaging. Never during a pregnancy and don't anticipate ever doing it.
My mother and I were just talking about this the other day. She said she asked the family doctor about an ultrasound when she was pregnant with me. He said to her, "Are you gonna to get an abortion if you see something wrong?" She said, "No." He said "Then you don't need one."
Years and years ago there was a study from Norway or Finland that said there was an increased risk of leukemia with one or more ultrasounds during pregnancy. I've seen way too many people told there was something wrong with the baby based on an ultrasound or even amniocentesis (sp?) and given birth to perfectly healthy babies later. Some of them were even specifically told by the doctor to have an abortion.
The day I realised I was pregnant with my daughter I knew I was having a girl. Everybody said I couldn't know that. I had a girl. I also told the people present at birth I was Strep B neg, and there was no issues with the blood type (I'm RH negative, hubby is positive). All of which everybody said I couldn't possible know. They were all true.
Aside from knowing I was having a girl, I have a friend who is a graphology expert. The kind who can testify at trials as an expert witness. He explained to me how to tell the sex from my handwriting and it also said girl. As far as knowing the sex, you can do handwriting or use a pendulum and find out. I know I'm having a girl again. Ironically, yet slightly less reliable, the Chinese gender calendar says girl for both of them based on my age and conception month. This time our RH types will be different, but it will be fine.
In my opinion, ultrasounds are for emergencies. I feel that way about all medicine personally. If you are in a car accident while pregnant, it might be a good idea to get one if there is any spotting afterwards. Any time there is really spotting and you need to know where the placenta is. As far as a routine "I want a picture of my baby" thing... Definitely not.
You can tell the babies position without an ultrasound, and there are also fantastic exercises you can do to help the baby stay head down naturally or turn the baby if necessary. They aren't 100%, but I did some just to be safe and my daughter was head down.
Reading a lot of other women's experiences (especially in the RH neg arena) and just knowing other women, it seems like the more interventions, the more problems. What comes first, the chicken or the egg? Probably sometimes there are more interventions because there are more problems and sometimes there are more problems because there are more interventions.
It would be really great if women could always be able to follow their gut instinct. Too many women tell me they didn't want to do this or that, but the doctor really pushed them.