BACKGROUND This study aimed to use a portable ultrasound method to quantitatively measure skin thickness and to compare leg edema in obese and non-obese pregnant women. MATERIAL AND METHODS Thirty-six pregnant women (17 primiparas and 19 multiparas) at 27/28 and 37/38 weeks of pregnancy, with and without leg edema, had their lower leg skin thickness measured using a B-scan portable ultrasonography device (72 legs and maximum of 98 measurements). Measurements were compared between women who were obese prior to pregnancy, with a body mass index (BMI) ≥25 kg/m² and non-obese with a BMI <25 kg/m². RESULTS Skin thickness of the legs in pregnant women with edema was significantly increased compared with that in pregnant women without edema (6.4±0.3 mm vs. 4.6±0.4 mm) (p=0.0001). There was a significant correlation between the degree of pitting edema and skin thickness in all edematous legs (r=0.56; n=98; p<0.0001). The cutoff level of edema measured by portable ultrasound in non-obese pregnant women was 4.7 mm (sensitivity 83.9%, specificity 66.7%) and was 7.5 mm in obese pregnant women. Obese pregnant women with edema had a significantly increased leg skin thickness compared with non-obese pregnant women with edema (11.3±1.3 mm vs. 5.7±0.2 mm) (p<0.0001). CONCLUSIONS Portable ultrasonography is a reliable method of quantitatively measuring skin thickness of the lower leg in edema associated with pregnancy. The thickness of the skin in obese pregnant women with edema can be expected to be significantly increased compared with non-obese pregnant women with edema.