Measurement of nuchal skin fold thickness in the second trimester: influence of imaging angle and fetal presentation
Bibliographic record
Abstract
OBJECTIVE: To assess the effect of imaging angle and fetal presentation on the measurement of nuchal skin fold thickness (NFT) in the second trimester. METHODS: Fetal NFT was prospectively measured in 921 women at 18-21 weeks' gestation. The population was divided into two groups according to fetal presentation. Group A comprised 643 fetuses in cephalic or transverse presentation and Group B comprised 278 fetuses in breech presentation. To determine whether there was a difference in NFT depending on imaging angle, in Group A the NFT was measured on the standard axial horizontal images and then on images obtained after moving the transducer about 30 degrees toward the occiput. In Group B an assessment was made as to whether NFT changed with fetal presentation. Initial measurements were made with the fetuses in breech presentation. Repeat NFT measurements were made after 15 min in 64 fetuses that had converted to cephalic or transverse presentation. Statistical analysis was performed using a paired t-test. RESULTS: The mean NFT on the standard horizontal image was 5.2 mm, while that on the 30 degrees occiput image was 4.0 mm. The difference was significant (P < 0.001). One hundred and twenty-three (19.1%) fetuses had a NFT greater than 6 mm on the standard image, but only two (0.3%) had an NFT of > 6 mm on the 30 degrees occiput image. There were no chromosomal or structural abnormalities in the 123 fetuses in which the NFT was > 6 mm. The mean NFT of 64 fetuses in the breech presentation was 4.4 mm, while it was 3.9 mm when they had converted to other presentations. The difference was statistically significant (P = 0.001). In breech presentation, 13/64 (20.3%) fetuses had a NFT greater than 6 mm compared to only one (1.6%) fetus in the other presentations. There were no structural or chromosomal abnormalities in any fetus with a NFT > 6 mm in either group. CONCLUSIONS: In this study the NFT measurement varied with scan direction and fetal presentation. To avoid falsely thickened NFT measurements the scan should be directed to image the posterior surface of the occipital bone. This can be achieved by scanning from a 30 degrees occipital direction. Also, NFT is greater in fetuses in a breech presentation. Attention to these details can reduce false-positive NFT measurements.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.019 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".