Objective

First-trimester fetal malformation screening via ultrasound has become increasingly important. This study aims to establish a standardized expert consensus on the ultrasound anatomical examination of fetuses during the first trimester.

Methods

A comprehensive literature review was conducted on first-trimester fetal anatomical examinations and malformation screening. A draft of the Chinese Expert Consensus on Fetal Anatomical Examination at 11 + 0 to 13 + 6 Weeks of Gestation was initially prepared by eight core committee members. Using the Delphi method, three rounds of online voting were conducted by 35 expert panel members, and feedback was solicited from 122 experts across 27 representative medical institutions of various levels and regions in China. If three-fourths of the expert panel members agreed to categorize the first-trimester fetal anatomical ultrasound examination into three types, these classification methods were adopted. Similarly, if three-fourths of the experts agreed that a specific item or plane in the consensus should be a mandatory component of the examination, it was designated as a recommended item or plane; otherwise, it was classified as a suggested item or plane.

Results

This expert consensus categorizes the first-trimester fetal ultrasound anatomical examination into basic (Class I), detailed (Class II), and targeted (Class III) examinations. The examination includes one measurement item (with six sub-items) and nine anatomical examination items (with 26 sub-items). The basic and detailed fetal anatomical examinations involve largely consistent measurement parameters and target organs. However, the detailed examination includes a greater number of sub-items. In the basic examination, biometric parameters such as biparietal diameter (BPD), head circumference (HC), and abdominal circumference (AC) are considered suggested items (not mandatory). Similarly, sub-items such as the primary palate, kidneys, and genital tubercle are also classified as suggested items. In contrast, all of these parameters are regarded as recommended items (mandatory) in the detailed examination. Both the basic and detailed fetal anatomical examinations are indicated for low-risk pregnancies. The primary distinction between the two lies in the level of healthcare facility where they are conducted. Basic examinations are suitable for county-level hospitals with screening qualifications, whereas detailed examinations should be performed at municipal-level hospitals with equivalent screening credentials. In the targeted examination of the fetal central nervous system (FCNS), a total of 11 ultrasound planes are included. Among these, 4 are designated as recommended planes, and the remaining 7 as suggested planes. In the targeted fetal cardiac examination, 5 planes are evaluated, with 4 being recommended and the bilateral subclavian artery plane classified as a suggested plane. In the targeted early pregnancy screening for cleft lip and palate, 5 planes are assessed, including 3 recommended and 2 suggested planes. Targeted examinations are primarily indicated for high-risk or suspected anomalous fetuses and should be performed at qualified prenatal diagnostic centers by certified physicians.

Conclusion

This consensus provides a robust framework for the standardized ultrasound anatomical examination of fetuses in the first trimester across medical institutions of varying levels and capacities. It also offers evidence-based support for future first-trimester fetal malformation screening.

Lyu, G., Liao, R., Jiang, Q. et al. Chinese Expert Consensus on ultrasound anatomical examination of fetuses at 11 + 0 to 13 + 6 weeks of gestation based on the Delphi method. Arch Gynecol Obstet (2025). https://doi.org/10.1007/s00404-025-08231-z