The anatomy scan, and what changes what it can see
Detection is not a fixed number.
The mid-pregnancy anatomy scan, usually at 18 to 22 weeks, is the main structural examination of the baby. How much it finds depends heavily on conditions.
In a study of more than 11,000 scans, the proportion of anomalous babies detected on a standard scan fell steadily with maternal body weight:
| Body mass index category | Detected on standard scan | Detected on a targeted scan |
|---|---|---|
| Normal weight | 66% | 97% |
| Overweight | 49% | 91% |
| Obese class I | 48% | 75% |
| Obese class III | 25% | 75% |
The chance of an anomaly still being present after a normal scan rose from 0.4% to 1.0%. Detection was also lower in women with diabetes before pregnancy: 38% against 88% for other high-risk indications.
If this applies to youAsk whether a targeted or detailed scan, rather than a standard one, is appropriate. The difference in the table above is large.
Where this comes from:
143. Dashe JS, McIntire DD, Twickler DM. Effect of maternal obesity on the ultrasound detection of anomalous fetuses. Obstet Gynecol. 2009;113(5):1001-1007.
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This page is educational. It supports the conversation with your own clinicians. It is not consent to any treatment, and it cannot assess you. If you are worried about a symptom now, see urgent warning signs.