Identification of fetal skeletal epiphyseal ossification centers on ultrsound can be a useful tool for estimating gestaional age, particularly at a time near fetal lung maturity.
Specifically the distal femoral epipyses (DFE) and the proximal tibial epiphyses (PTE) can be used.
- distal femoral epipyseal (DFE) ossicifation center
- may be seen as early at 29 weeks of gestation
- can be seen at 33 weeks in most fetuses
- when the DFE was greater than or equal to 7 mm the gestational age was greater than or equal to 37 weeks.
- proximal tibial epiphyseal (PTE) ossificiation center
- if seen it can be assumed that the fetus is at least 35 weeks gestation
Several precautions should be taken
- while the presence of these centers may be helpful in determining fetal gestational age and / or lung maturity their absence does not indicate that a fetus is necessarily earlier in gestation or does not have fetal lung maturity
- adjacent structures to the cartilaginous centers ie synovium or capsule should not be misinterpreted as the epiphyseal centers
- the identification of a DFE of any size may not correlate with fetal lung maturity particularly in complicated pregnancies, such as the diabetic patient.