OC137: Normal values for fetal abdominal subcutaneous fat from 20 to 40 weeks gestation, measured using speckle reduction software
Objectives
To report normal values for fetal abdominal subcutaneous fat thickness from 20 to 40 weeks gestation using speckle reduction software.
We have previously shown that the amount of subcutaneous fetal abdominal fat (FAF) reflects fetal nutrition and that the fetuses with less than 5 mm of FAF at 38 weeks gestation were five times more likely than those with > 5 mm of fat, to have a birth weight below the 10th percentile. Other investigators have reported that although fetal fat accounts for only 12 to 14% of birthweight, it accounts for 42% of its variance. Measurement of fetal abdominal subcutaneous fat may, therefore, predict fetal growth restriction or macrosomia.
FAF thickness is easily measured in the same anatomical plane used to measure the abdominal circumference, and we have previously reported on the methodology employed. Modern speckle reduction software enhances the identification of tissue interfaces, facilitating measurement.
Methods
600 healthy non smoking caucasian women with normal fetuses had a single measurement of fetal abdominal subcutaneous fat performed during pregnancy. The measurements were evenly distributed throughout pregnancy and each patient had only one measurement used. Fat thickness was measured in the same image as that used to measure abdominal circumference, using magnification, and employing speckle reduction to better identify margins. The average of 3 separate readings was used.
Results
Fetal abdominal subcutaneous fat increased from a mean value of 1.87 mm at 20 weeks to 6.05 mm at 40 weeks. The mean value and 5th and 95th percentiles from 20 to 40 weeks are given in the table. These results are similar to those obtained in previous smaller studies. Further investigation may determine whether deviations from normal fat values might predict intra-partum complications such as dysfunctional labour or shoulder dystocia.
| Gestation wks | 20 | 22 | 24 | 26 | 28 | 30 | 32 | 34 | 36 | 38 | 40 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Mean FAF mm | 1.87 | 2.18 | 2.57 | 2.73 | 3.26 | 3.52 | 4.24 | 4.57 | 5.52 | 5.74 | 6.05 |
| 5th percentile | 1.20 | 1.30 | 1.78 | 2.22 | 2.30 | 2.78 | 3.10 | 2.78 | 4.22 | 4.15 | 4.10 |
| 95th percentile | 2.60 | 3.40 | 3.41 | 3.39 | 4.10 | 4.61 | 5.63 | 6.26 | 7.38 | 7.18 | 8.12 |
