Imaging studies

Participants in both the intervention and expectant management group will undergo two fetal MRI examinations. The first MRI exam will occur during the study screening period. The second MRI exam in participants enrolled in the intervention arm will occur at a minimum after four therapeutic amnioinfusions, between 30- and 32-weeks gestational age. For those in the expectant management groups the second fetal MRI will occur at the 32 week assessment visit. The fetal lung (volume and Apparent Diffusion Coefficient (ADC)) and brain (ADC and ventricular size) will be evaluated during the course of enrollment.