Obstetric Ultrasound, Second Trimester

A second-trimester obstetric ultrasound is performed using ultrasonic waves to visualize the fetus and placenta in the uterus. This test is less successful at determining the estimated date of confinement than a first-trimester ultrasound but the fetus's organs, including its external genitalia (gender), can be determined after approximately 16 weeks' gestation.