Abnormal fetal skeletal morphology Reduced fetal femur/foot length ratio 2022-01-11T13:25:51Z This ratio relates the length of the fetal femur to that of the fetal foot. The ratio is approximately 1 throughout the age range of 14 to 40 weeks of gestation. A substantial reduction in the raio can help differentiate fetuses that have dysplastic limb reduction from those whose limbs are short because of constitutional factors or IUGR. It can reduce the problem of an unknown gestational age and help to distinguish between fetal skeletal dysplasia and intrauterine growth retardation caused by other factors.