Indications for obstetric ultrasound in the second and third trimester
There are numerous indications for US imaging in the second (and third) trimester, the most common ones including screening evaluation of fetal anatomy; screening for fetal anomalies; estimation of gestational age; and evaluation of fetal growth, fetal well-being, fetal presentation, cervical insufficiency, amniotic fluid status, placental location, and vaginal bleeding.
In most circumstances, US in the second and third trimester only requires transabdominal imaging. Transvaginal or transperineal imaging may be required for more detailed evaluation of the cervix and placental position in cases with placenta previa, suboptimal visualization of the cervix, or with a shortened cervix on transabdominal imaging.
