Ultrasound measurement of fetal growth in Macaca nemestrina

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Abstract
Longitudinal ultrasound data were collected for 18 structures in 37 pigtailed macaque (Macaca nemestrina) fetuses to 1) generate standards of normal fetal growth, 2) measure operator reliability, 3) assess the accuracy of linear and nonlinear regression models to estimate gestational age and dates of delivery, and 4) evaluate the portability of equations and absolute values derived from data at one facility (Seattle) to describe independently collected data on the same species at another facility (Medical Lake Breeding Colony). Femur length, biparietal diameter, and head area were found to be the best predictors of gestational age, as judged by maximum “explained” variance (R2) with minimum error estimates. Days to delivery could not be adequately predicted by any single fetal growth parameter or by the best combination of parameters. Operator reliability was very good: error was ⩽5% over all parameters studied. Although the form of growth curves from each facility was generally the same, variability was much greater for most parameters at Medical Lake, and both femur and humerus lengths were overestimated relative to the Seattle data. The same result was obtained for femur length when Seattle data on pigtailed macaques were compared with published data on rhesus macaques. We believe that these differences in facilities and populations may be due to the practices of the ultrasound operators. We suggest that portability of regression coefficients and absolute values for structures at a given gestational age can be accomplished only if operators are trained to use the same standard methods and receive periodic reliability checks.