1. Skinfold thicknesses at seven sites were measured during and after pregnancy in eighty- four women; in forty-eight of these, total body water was measured concurrently.
2. Early in pregnancy (10 weeks) the skinfold measurements were highly correlated with each other and with maternal weight, ratio of observed weight to standard weight-for-height,‘dry’ (water-free) weight, and with calculated estimates of body fat.
3. At nearly all sites, skinfold thicknesses increased up to about 30 weeks of pregnancy. Increases were greater at ‘central’ and least at ‘peripheral’ sites, and were not proportional to the initial skinfold thickness.
4. From 30 to 38 weeks of pregnancy, the patterns were variable: the mid-thigh skinfold continued to increase and at the other sites there was little change or a decrease.
5. All sites decreased by a surprisingly large amount between 38 weeks of pregnancy and the end of the first post-partum week. The evidence suggests that this change, which was not related to the presence or absence of oedema, occurred about the time of parturition.
6. From the end of the first post-partum week to 6–8 weeks post partum, the changes were again variable.
7. The increase of skinfolds during pregnancy was greater in underweight than in overweight women, and in primiparae than in multiparae. The pattern of change was not affected in any consistent manner by oedema.
8. The changes in skinfold thicknesses during pregnancy, especially up to about 30 weeks, showed patterns similar to those of total body-weight and ‘dry’ body-weight. A formula is given by means of which ‘dry’ weight can be predicted from five skinfolds, height and duration of gestation.