The Fetal Arm

Abstract

Objective. The goals were to introduce fractional arm volume (AVol) as a new soft tissue parameter of fetal growth assessment and to develop individualized growth standards, based on Rossavik models, for AVol, midarm circumference (ArmC), and humeral diaphysis length (HDL). Methods. A prospective longitudinal study of 22 fetuses was conducted using 2-and 3-dimensional sonography. Three new growth parameters (HDL, ArmC, and AVol) were used to establish individualized standards for arm growth with the use of Rossavik functions [P = c(t), where P is the anatomic parameter; c, k, and s are model coefficients; and t is the time variable]. Second-trimester models were specified from the linear slopes of growth curves before approximately 28.0 menstrual weeks. For a given fetus, normal thirdtrimester trajectories were predicted for each parameter. Observed and predicted measurements were compared by percent deviations. Results. Rossavik functions fit all parameter trajectories extremely well (R 2 = 95.7%-99.4%). By fixing coefficients k at their mean values, their respective fits did not change, and the variabilities of both coefficients c and s were reduced. Coefficient c was also significantly related to second-trimester slope, as was s to c, for all 3 parameters (R 2 = 97.7%-98.7%; P < .0001). Mean percent deviations between observed and predicted third-trimester HDL, ArmC, and AVol measurements were -0.1% ± 2.9%, 0.5% ± 4.6%, and 0.4% ± 8.5%, respectively. Conclusions. Individualized growth assessment, using HDL and ArmC, can accurately predict normal arm growth during the third trimester of pregnancy. AVol may also allow earlier detection and improved monitoring of soft tissue abnormalities that can occur in fetuses with growth disturbances.

Defining the Normal Growth Curve of Fetal Fractional Limb Volume in a Japanese Population

“…This growth pattern replicated the prior report of fractional limb volume growth in the United States [12]. Fractional limb volume is composed of fat mass and lean mass; the critical time of fractional limb volume growth acceleration is in the early third trimester [20,21], which coincides with the period of accelerated fetal fat deposition [8,14]. Fetal fat deposition is histologically evident at 14-16 weeks of gestation [22]; however, fetal soft tissue has been reported to accumulate mainly in later gestation, while fat deposition typically accelerates after 30 weeks of gestation [8,14].…”