From the Guidelines
Ultrasound examinations should be performed between 18-20 weeks of gestation for routine screening of fetal anomalies, as recommended by the Eunice Kennedy Shriver National Institute of Child Health and Human Development 1. The American College of Radiology also supports this recommendation, outlining the components of a standard fetal examination at 18-20 weeks in the ACR-ACOG-AIUM-SMFM-SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound 1. Some key points to consider when performing ultrasound examinations at this gestational age include:
- The mid-trimester anatomy scan should be performed between 18-22 weeks when fetal structures are well developed but still easily visualized.
- For high-risk pregnancies, additional ultrasounds may be needed at 28-32 weeks to assess fetal growth and placental function.
- A third trimester ultrasound between 32-36 weeks may be indicated to evaluate fetal position, growth, and amniotic fluid volume. It's essential to note that the specific timing of ultrasound examinations may vary based on individual risk factors, such as maternal diabetes, hypertension, or previous pregnancy complications 1. However, the most recent and highest-quality study, which is the 2021 study by the Journal of the American College of Radiology 1, recommends the 18-20 week gestation period for routine screening. Therefore, the recommended gestational age for ultrasound examination is between 18-20 weeks.
From the Research
Gestational Age for Ultrasound
- The American Institute of Ultrasound in Medicine's guidelines, as reviewed in 2, suggest that a complete second trimester ultrasound should be performed between 18 and 22 weeks of gestation.
- This period is considered optimal for diagnosing fetal anomalies and assisting in the management of prenatal care 2.
- A study published in 3 compared the effects of routine ultrasound before 24 weeks' gestation and found that second trimester scans probably make little difference to perinatal loss, but may improve detection of multiple pregnancy and major fetal abnormalities.
- Another study 4 used Doppler ultrasound to investigate complications like fetal growth restriction and fetal distress in high-risk pregnancies after 28 weeks of gestation.
Ultrasound Frequency and Timing
- The Society of Obstetricians and Gynaecologists of Canada recommends that pregnant women be offered a routine second trimester ultrasound between 18 and 22 weeks' gestation 2.
- First trimester routine ultrasound may reduce short-term maternal anxiety, while second trimester scans may reduce induction of labor for post-maturity and improve detection of major fetal abnormalities 3.
- There is no clear evidence on the optimal frequency of ultrasound examinations during pregnancy, but it is generally recommended to perform them as needed, based on individual patient risk factors and fetal development 3, 2.