Limitations
We acknowledge several limitations. First, its retrospective design may
result in selection bias as we included only cases with more than one
good quality MRI examination. Second, as a fetal surgery center, the
group of fetuses with severe hypoplasia is overrepresented; in addition
most of them received a prenatal intervention, which changes the natural
history 6, 7, 24. Third, we have no standardized
postnatal follow up information on these cases, as many patients do not
deliver in our center.