Premature Restriction of Foramen Ovale in an Anemic Fetus From a Rhesus-negative Mother: A Case Report

Rhesus (Rh) negative women who are exposed to Rhpositive red blood cells (RBCs) (e.g., those who deliver a D-positive baby) are at the risk of developing anti-D antibodies against the Rh antigens present on the surface of RBCs. Memory response of maternal immune system in subsequent re-exposures makes Ig G antibody which is transferred across the placenta into the fetal circulation. Rh-positive fetuses from these mothers are at the risk of serious morbidity and mortality, and a group of disorders such as severe hemolytic anemia, hydrops fetalis, and intrauterine fetal demise if not treated. The fetal middle cerebral artery-peak systolic velocity (MCA-PSV) is a noninvasive tool for the diagnosis of fetal anemia. The sensitivity of MCA-PSV> 1.5 MoM (multiples of the median) is 100% for the prediction of moderate or severe anemia in the fetuses never transfused with a false positive rate of 12% (1). During intrauterine life, foramen ovale (FO) is the only pathway for the oxygenated maternal blood to enter from the right atrium of the heart to the left one and then being pumped into the upper part of fetus’s body (2). Premature closure or restriction of the FO is a rare and serious clinical condition that prevents this normal fetal blood circulation. It can be associated with fetal arrhythmia, right -side heart failure, pericardial effusion, tricuspid regurgitation (TR), non-immune hydrops fetalis, and intrauterine fetal death with unknown causes during the pregnancy (3,4). Premature restriction of FO is diagnosed based on the following criteria (5): • An FO diameter <3 mm with a Doppler velocity measured gradient >5 mm Hg or • FO diameter <2 mm with Doppler velocity >120 cm/s In this study, a case of premature restriction of FO was described in a fetus from the RH alloimmunizated mother who had severe intrauterine hemolytic anemia not detected antepartum by routine Doppler ultrasound examination of MCA-PSV-MoM..