Routine first-trimester ultrasound screening using a standardized anatomical protocol

Background: First-trimester ultrasound scans were introduced to China for nearly 20 years. The ability of first-trimester ultrasound screening to detect different malformations was variable. A recent systematic review concluded that the use of a standardized anatomic protocol was the most crucial factor to improve the sensitivity of first-trimester ultrasound screening for anomalies. Standardized sectional scans have long been used for routine anatomy screening during the second trimester. However, during the first trimester, most of the previous studies have described the observation of anatomic structures but have not specified clearly the standard sectional views.

Objective: We aimed to determine the performance of routine first-trimester scans using a standardized anatomic protocol for detecting structural abnormalities in China.

Study design: This was a large retrospective study involving 59,063 sequential unselected pregnancies. Scans at 11 to 13⁺⁶ weeks were performed in a single center during a 7-year span. All fetuses were examined following a predefined protocol for standardized views.

Results: From October 2008 to December 2015, first-trimester scans were performed in 53,349 pregnant women with available outcome. Of these, there were 1578 (3%) pregnancies that presented with at least 1 fetal structural abnormality. The detection rate for first-trimester screening was 43.1% (95% confidence interval, 40.6%-45.5%). Routine first-trimester scans detected 95.6% of abdominal wall defects, 66.3% of nervous system defects, 33.8% of limbs and skeleton malformations, 30.8% of facial abnormalities, 21.2% of urogenital abnormalities, 18.4% of thoracic and lung abnormalities, and 4.1% of gastrointestinal tract abnormalities. During the first trimester, 37.7% of cardiac defects were identified and included 57.9% of major cardiac defects and 2.6% of mild cardiac defects. A robust high detection rate for anencephaly, exencephaly, cephalocele, holoprosencephaly, exomphalos, gastroschisis, Pentalogy of Cantrell, sirenomelia, and body stalk anomaly was achieved during routine first-trimester scans.

Conclusion: A standardized anatomic protocol is advised when performing routine first-trimester ultrasound screening. It is recommended that screening for severe structural abnormalities should be extended to the first trimester.