Prenatal ultrasounds are not 100% accurate. Readings also depend on the training and experience of the tech and the ob. Ultrasonography cannot detect certain anomalies in the fetuses. There have been cases when fetuses have been aborted to find out, in the post-mortem, that they were perfectly normal. But, ultrasound remains a great diagnostic tool and many lives have been saved by it.
See 1 more doctor answer