CHANGES IN TOTAL-BODY FAT DURING THE HUMAN REPRODUCTIVE-CYCLE AS ASSESSED BY MAGNETIC-RESONANCE-IMAGING, BODY-WATER DILUTION, AND SKINFOLD THICKNESS - A COMPARISON OF METHODS

Total body fat and fat-free mass were assessed by magnetic resonance i maging (TBFMRI and FFMMRI) in 11-16 healthy Swedish women before pregn ancy and 5-10 d and 2, 6, and 12 mo after delivery. On these occasions , TBF was also measured by the body water dilution (TBFBWD) and skinfo ld-thickness (TBFSFT) techniques. The results were used to compare cha nges in TBFSFT and TBFBWD during reproduction with changes in TBFMRI. TBFBWD was 1.5-4.0 kg higher than TBFMRI and at all postpartum measure ments the difference between these estimates increased significantly w ith increased body fat content. This difference was also significantly higher 6 mo after delivery than it was 2 and 12 mo postpartum. The po ssibility that this was due to variations in the degree of hydration o f FFM postpartum was considered. TBFSFT was 1.7-3.1 kg higher than TBF MRI and this difference increased with increasing body fat content. Th e agreement between changes in TBFMRI and TBFSFT was different during different times in the reproductive cycle and was also influenced by t he amount of fat lost or gained. The findings thus suggest that there is a risk for bias when changes in TBF during reproduction are estimat ed by the skinfold-thickness technique as well as by isotope dilution.