List five reasons why examination of the fetus by ultrasound in the second trimester is particularly useful.

1. Organs are fully formed
2. Anatomy is easier to visualize
3. Most congenital anomalies can be detected at 18 to 20 weeks' gestational age.
4. Detection of congenital anomalies allows for treatment planning, alteration of obstetric care, parental counseling, genetic screening, and optimal planning for delivery.
5. Abortion may be an option before 24 weeks if major anomalies are detected.