Ultrasound is totally harmless, but doctors recommend ALARA ("as low as reasonably achievable"). Average baby is exposed to 50 - 90 minutes of ultrasound over three visits, though we had to go more frequently for scans for all three of my kids. This would be 36 minutes if you went in every week. If it was possible to get medical quality anatomy scans and avoid transvaginal scans (either because of the tech or simply just going reguarly enough to catch all the imaging you need) then it would win the entire US market for sure: roughly $3-7B for the ultrasounds (3.5M US births at $1-2k per for ultrasounds). also it's a spa -- prenatal wellness spend in the US estimate at $5-7B.

They don’t recommend them overly frequently because it’s unnecessary, but it’s not harmful to mom or the baby in any way.