Premium
Measurement of nuchal skin fold thickness in the second trimester: influence of imaging angle and fetal presentation
Author(s) -
Cho J. Y.,
Kim K. W.,
Lee Y. H.,
Toi A.
Publication year - 2005
Publication title -
ultrasound in obstetrics and gynecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.202
H-Index - 141
eISSN - 1469-0705
pISSN - 0960-7692
DOI - 10.1002/uog.1847
Subject(s) - medicine , occiput , breech presentation , presentation (obstetrics) , fetus , skin fold , occipital bone , cephalic presentation , anatomy , nuclear medicine , pregnancy , obstetrics , skull , pathology , biology , genetics , body mass index
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° 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° 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° 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° occipital direction. Also, NFT is greater in fetuses in a breech presentation. Attention to these details can reduce false‐positive NFT measurements. Copyright © 2005 ISUOG. Published by John Wiley & Sons, Ltd.