Objective Fetal fractional limb volume has been proposed as a useful measure for quantifying fetal soft tissue development. The aim of this study was to investigate the growth of fractional arm volume (AVol) and fractional thigh volume (TVol) of fetuses with maternal gestational diabetes (GDM) compared with those of fetuses with normal glucose tolerance (NGT). We hypothesised fetal fractional limb volume would be larger in the GDM group than in the NGT group in late gestation. Design Exploratory observational study. Setting Saitama Municipal Hospital. Sample A total of 165 (125 NGT and 40 GDM) singleton Japanese pregnant women. Methods AVol and TVol were assessed between 20 and 37 weeks’ gestation as cylindrical limb volumes based on 50% of the fetal humeral or femoral diaphysis length. Women were diagnosed as GDM based on the criteria of the Japan Society of Obstetrics and Gynecology. Main outcome measures AVol and TVol were compared between women with NGT and those with GDM at each gestational age period (2‐week intervals from 20 to 37 weeks’ gestation). Results Overall, 287 ultrasound scans were performed (NGT group, 205 scans; GDM group, 82 scans). There was no significant difference of AVol between the groups before 32 weeks’ gestation. AVol was significantly larger in the GDM group than in the NGT group after 32 weeks’ gestation (P < 0.05). TVol was not statistically different between the groups across gestation. Conclusions Detection of variations in fetal AVol may provide greater insight into understanding the origins of altered fetal body proportion in GDM. Tweetable AVol, but not TVol, is significantly larger in fetuses with GDM than in those with NGT after 32 weeks’ gestation. Tweetable AVol, but not TVol, is significantly larger in fetuses with GDM than in those with NGT after 32 weeks’ gestation.