The aim. To compare the relation between the changes in the body and breast size in pregnant and young nulliparous women. Materials and methods. In 2008-2009, 82 young nulliparous nineteen-year-old women were examined in Šiauliai (Study I). Their body mass and breast size data were compared with the findings obtained from the examination of pregnant women during their first trimester in Vilnius from 2013 to 2015 (Study II). These findings involved longitudinal and transverse dimensions, the volume of various parts of the body, skin folds, breast dimensions, waist, hips, body mass indices, breast volume, and passive body mass. Both studies used standard anthropometric techniques and Martin instruments. The breast volume was calculated according to the formula of Kramer and Dexler (1981). The percentage of the passive body mass (fat tissue) were determined from the skin folds and the subcutaneous adipose tissue according to the formulae of Wilmore and Behnke (1970), and of Siri (1961). The differences between the groups were assessed by Student's t test. The selected reliability level was p < 0.05. Results. The following indicators were found to be statistically significantly higher in the group of pregnant women: chest, waist, hips, breast volume and the waist-hip index. The adipose tissue in pregnant women increased in the upper part of the body, although the relative and absolute passive body weight between the groups differed insignificantly. a comparison of the measurements of primiparous and multiparous young women with the measurements of the nulliparous subjects shows that the multiparous women had a larger amount of fat tissue, while in primiparous and young nulliparous women these indicators were not significantly different. Body size indices of the subgroups of pregnant women with small, medium, and large breasts were higher than those of the young nulliparous with similar measurements. The body size of lean women (below 25 percentile) was higher than that of young nulliparous women in the group of pregnant women. Differences in the body size indices of medium obese women (between 25 and 75 percentiles) were similar to the indicators of medium-sized female breasts in the group of pregnant women. The differences found in obese women (above 75 percentile) were similar to the indices recorded in the women of medium obesity. Conclusions. The passive body mass of pregnant women was accumulating in the upper part of the body. The body mass index in pregnant women was higher than that in nulliparous young women. Over the course of time (the age difference between the studied groups was ~10 years), the female body increases, the topography of the distribution of the adipose tissue changes. Pregnant women's breast volume was significantly higher than that of young nulliparous women. This phenomenon can be explained by pregnant women's higher passive body mass and older age. Keywords: anthropometry, passive body mass, pregnancy, breasts.