This late 3rd trimester patient reported that her daughter"s activity reduced significantly 2 days ago. The biophysical profile was 4/8. The baby was delivered that evening and had an uneventful postnatal course.

The following are images from her scan. They demonstrate a small cystic structure in the left atrium. This cystic structure is the bulging foramen ovale flap. Note the lack of opening of the foramen ovale flap and the absence of motion during the cardiac cycle. If this was simple an aneurysm of the foramen ovale flap it would indeed balloon in the left atrium but an opening would be visible. Another difference is that the interventricular septum is slightly deviated to the left cavities indicating right-sided over pressures. There is also a sliver of pericardial fluid.

These are images obtained on day 5 of life of the baby. One can recognize the deflated foramen ovale that is partially collapsed (arrow). Note that in the postnatal images the traditional adult orientation is used so that now the apex is pointing to the left of the patient but the right of the image.

So the final diagnosis was indeed that of premature closure of the foramen ovale.