Disclaimer: I am not a doctor. Please consult your own medical caregivers for medical advice.
I've been meaning to write about this topic for months now, but I haven't managed to express myself clearly enough. Rabbi Lazer Brody expresses many of my thoughts about prenatal ultrasound here and here.
The facts are clear: There is no scientific evidence that the routine use of ultrasound improves the outcome of pregnancy for the mother or baby. Its long-term safety for mother and baby have not been adequately studied (though there's no evidence of danger.) The professional organizations in the U.S., for example, recommend the use of prenatal ultrasound only when "medically indicated" - i.e., when there's already evidence of a problem that needs to be diagnosed. Not as a routine tool used frequently (that's how it's used in Israel).
Rebooting the baby
Ultrasound scans for fetal defects have a high rate of "false positives" - that is, false indications of problems that don't really exist. This sends both parents and their doctors into a panic, and abortion is often advised. "You can always try again" is the attitude, often expressed explicitly by doctors. As if a baby can just be rebooted and started from scratch. As if anything that deviates from the norm is inherently suspect ("Ear looks too small, foot looks too big - might be a problem"). As if biological processes can ever be perfect, no matter how much technology we throw at them.
Furthermore, they have a high rate of "false negatives" - that is, they fail to identify a large number of problems which actually exist. Then the parents, made complacent by their doctors' assurances that everything looks fine, are shocked to discover undiagnosed defects (God forbid) when the baby is born. Is false complacency better than pure ignorance?
We're number one!
You may be surprised to learn that Israel leads the world in fetal testing. We left one early prenatal visit with a page-long list of recommended tests, everything from genetic screening to fetal anatomy ultrasound scans. The implication was that we were expected to have all of them done - no advice was given as to the drawbacks of any of the tests, or the possible advantages of having them. Many of them are also not covered by national health insurance here, and some are quite expensive.
What the doctors fail to mention is that most prenatal tests are not conclusive. You're left with a statistical indication - some better than others, but nonetheless not a certainty. What they also don't tell you is that in nearly all cases, there's no treatment that can be administered as a result. If something is (apparently) wrong, the only "remedy" is abortion.
We determined very early on that we would not consider abortion on the basis of less than 100% certainty of a serious problem. (I'm not a rabbi, but I also believe this is the clear consensus of halachic authorities.) Since none of the tests can provide that certainty (not even amniocentesis, which causes miscarriages more often than it identifies problems), we saw no reason to have them done.
(We eventually relented on the skirat maarchot murchevet, the "extended anatomy scan", due to heavy pressure from our caregivers. In retrospect, I regret having done it. It caused us unnecessary worry by identifying nonexistent "problems" which cleared up on their own over time.)
Running long lists of tests on apparently-healthy fetuses entrenches the presumption that pregnancy is a situation always on the brink of disaster. It instills fear into parents, who are led to believe that if they skip the tests they are acting irresponsibly. The fetal anatomy scan, which I gather was invented in Israel and is virtually standard here, is the worst example. The doctor will proceed through a checklist of organs making sure each is "okay" - that is, conforming to the normal expectations. Statistically, if you run enough tests, some of them will be positive. That doesn't necessarily mean anything is actually wrong. (On top of that, they also offer an "early anatomy scan" to catch some problems the later scan can't see.)
Perfection through technology
Healthy babies are born all over the world without a single ultrasound scan. Even today in Europe and North America, many pregnancies proceed without recourse to ultrasound, or using it only when medically indicated.
What is it about Israel? Are Israeli parents so terrified of abnormalities that they must run every test in the book? Are Israeli doctors so terrified of malpractice suits that they dare not let a defect slip through when it's always possible to abort? Are Israelis so obsessed with technology that they believe life can be sterilized from all doubt and risk with sufficiently advanced equipment?
As Rabbi Brody notes, thousands of abortions are performed in Israel every year on the basis of highly-uncertain test results. Rav Ovadiah Yosef commented on this a few months ago, calling on women not to have abortions due to "defects" identified on ultrasound.
I'm not a Catholic. Jewish law permits abortion in limited circumstances, mostly when the mother's life is in danger. I can't imagine, though, that any rabbi would permit abortion due solely to a doctor's interpretation of statistically uncertain medical tests.
Medical technology can accomplish wonderful things. Let's not allow our appreciation for technology to blind us to its limitations. No one can guarantee you a perfect baby. For that, your only recourse is prayer.