Combining Detailed Fetal Anatomy Scanning in the NT Window Versus Early Second Trimester Scanning at 14-16 Weeks: A...

Area of Science:

• Maternal-Fetal Medicine
• Diagnostic Ultrasound
• Prenatal Diagnosis

Background:

• First-trimester ultrasound commonly includes nuchal translucency (NT) screening and fetal anatomy scans (FAS).
• Current practice often involves two separate visits: one for NT screening and a later one for detailed FAS.
• This two-visit protocol typically separates NT screening (11-14 weeks) from detailed FAS (14-16 weeks).

Purpose of the Study:

• To evaluate if an integrated approach, performing detailed FAS within the NT screening window, is non-inferior to the standard two-visit protocol.
• The study aimed to assess the diagnostic yield of detecting fetal anomalies with an integrated scan versus a split protocol.
• To determine if earlier detailed fetal assessment compromises the detection of congenital anomalies.

Main Methods:

• A prospective study enrolled 755 pregnant women (singleton gestations) into two groups: integrated NT+FAS (n=243, 12.5-13.6 weeks) and a two-visit group (n=512, 14-16 weeks).
• All participants underwent mid-trimester follow-up scans (20-24 weeks).
• Scans adhered to International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) guidelines, with non-inferiority defined by a ≤6% difference in anomaly detection rates.

Main Results:

• The integrated NT+FAS group identified anomalies in 7.5% (16/243) of fetuses, compared to 3% (16/512) in the two-visit group (P=0.033).
• Mid-trimester follow-up revealed additional anomalies in 0.9% (2/227) of the integrated group and 0.8% (4/496) of the two-visit group (P=1.0).
• The integrated approach met the non-inferiority criteria for diagnostic yield.

Conclusions:

• Performing a detailed fetal anatomy scan during the final week of the NT screening window is diagnostically equivalent to the traditional two-visit approach.
• This integrated first-trimester protocol allows for earlier fetal anomaly detection and parental reassurance.
• The integrated approach does not compromise the overall diagnostic accuracy for detecting fetal abnormalities.