The main purpose of this scan is to rule out the presence of fetal anomalies, which means abnormalities in the development of baby’s body. It entails a detailed look at the fetal anatomy: head, brain, face, heart, spine, chest, abdomen, stomach, kidneys, bladder, arms, hands, legs and feet. At this scan, the sex of the fetus can be determined. Measurements will be taken to assess fetal growth and the amniotic fluid volume. The location and position of the placenta will be assessed as well.
An anatomy scan is mainly performed using a transabdominal probe, this means it is carried out by placing an ultrasound transducer on your abdomen. In selected cases, a transvaginal scan may be required. It is ideally done between 18-21 weeks of gestation.
Assessment of the cervix length by ultrasound is helpful in determining the risk of early (premature) delivery. The Society of Maternal-Fetal Medicine (SMFM) now recommends routine transvaginal cervical length screening for both high-risk (multiple pregnancies, those with a previous preterm birth, abnormalities of the uterus or previous cervical surgery) and low-risk patients (SMFM Consult Series #40: The role of routine cervical length screening in selected high- and low-risk women for preterm birth prevention).
If the placenta is low at the anatomy scan, we will recommend a repeat ultrasound scan at 30 weeks to check the location of the placenta. Most placentas that are described as “low-lying” at the anatomy scan will not be low-lying anymore at the follow-up scan at 30 weeks. A transvaginal ultrasound may be the most accurate method to assess the placental position.
