30 years ago having an ultrasound during pregnancy was rare. 15 years ago one was routine. Now women get lots of ultrasounds for no medical reason other than they are pregnant.
The first tends to be at the beginning to date the pregnancy. It drives me crazy to hear of women who were actively trying to conceive and absolutely sure of their dates accepting the ultrasound date their doctor gives them. Never mind first trimester ultrasounds, while the most accurate for dating, are still +/- 5 days. (And don’t get me started on doctors changing due dates based on second and third trimester ultrasounds!)
The last ultrasound women tend to get is right near the end of their pregnancy to assess the size of the baby. They call them growth scans. Apparently doctors are unable to feel the baby in utero through the mother’s belly and estimate the size of the baby. Instead they need the ultrasound machine to tell them how much the baby weighs. And now that, somehow, 8-9 pounds has become such a huge size (never mind the average female is 7-8 and the average male is 7-12 at birth) doctors use these growth scan estimates as a way to scare women into being induced early to avoid a “big” baby or to forgo labor all together and have a scheduled c-section.
There’s a huge problem with those late pregnancy growth scans. Third trimester ultrasound weight estimates are +/- 3 whole pounds! So they can say the baby is 9 pounds but in actuality the kid is only 6. Large heads, chubby bellies, long leg bones, and more can contribute to the estimates being so far off. I was told at 34 weeks Cameron was already 6 1/2 pounds. He was born 7 1/2 weeks later at 6 pounds 6 ounces, smaller than the ultrasound said he already was almost 2 months before. He had a big head and was long, but skinny which led to the completely wrong size estimate.
What I find most interesting, however, is that midwives tend to be so much better than ultrasounds at estimating the baby’s size simply by putting their hands on the mom’s belly and feeling the baby. Rarely have I heard of a midwife more than a pound off and never have I heard of one estimating 3 pounds off. Two days before Fritz was born my midwife said she thought he was 7 1/2-8 pounds. He was 7-13 at birth.