Eleven healthy women, age 28.7 ± 4.9 and body mass indices between 18.2 and 37.3kg/m2, carrying singletons were measured at 20 ± 1 and 30 ± 1 week gestation. Tricep, bicep, mid-thigh, subscapular and suprailiac sites were measured in triplicate on the left side of the body using Lange skinfold calipers (Cambridge Scientific Industries, Cambridge, MD). Mid-arm, abdomen, hip and mid-thigh circumferences were measured using a non-strechable tape. Sonogrpahic measurements of fat thickness were performed using either a 3.5 or 5 MHZ probe. Mid-thigh fat thickness increased by 2.4mm, from 30.3mm at 20 weeks to 32.7mm at 30 weeks (8.0% increase) when measured by skinfold calipers. The mid-thigh fat thickness rose from 7.9mm to 9.8mm from 20 to 30 weeks, a 1.9mm or 23.8% increase when measured by ultrasound. The suprailiac fat thickness increased by 1.8mm using both methods of measurement (7.5% increase by skinfold calipers and 17.7% increase using ultrasound). Slight decreases in fat thickness were detected at the subscapular site (0.9mm using skinfold calipers, 0.3mm using ultrasound). No appreciable changes were detected in fat thickness at the tricep and bicep sites using either method. Using the SPSSPC+ statistical software version 4.1 (Chicago, IL) t-test, there was no significant difference between the two methods in estimating the change of fat thickness during this interval in singleton gestation.