Fetomaternal Hemorrhage: A Review after a Case Report

Fetomaternal hemorrhage (FMH) consists in the transmission of fetal blood cells into the maternal circulation. Although the pathophysiology is not yet completely understood, it is likely to occur in small volumes in all pregnancies, with no apparent clinical significance in most cases. The incidence of clinically significant fetomaternal hemorrhage varies widely depending on the cutoff used to define it  Considering only the volume lost is probably insufficient as the rate of blood loss is also an important factor. Many studies defined 30 mL as threshold for meaningful fetal blood volume and 80 mL or 150 mL as cutoff to define “large” or “massive” fetomaternal bleeds . Massive fetomaternal hemorrhage is more likely to be fatal if blood loss occurs over minutes rather than hours, days, or weeks.

The blood pressure is higher in placental blood vessels than in the intervillous space. If the maternal-fetal barrier is disrupted, hemorrhage will occur from the fetus to the maternal circulation. Incidence increases with gestational age, and so does the volume of fetal blood in the maternal circulation. Some risk factors such as external cephalic version, abdominal trauma, manual removal of the placenta, placental abruption, monochorionic monoamniotic twins, preeclampsia, placental tumors, and amniocentesis have been associated with fetomaternal hemorrhage. However, no cause is identified in over 80% of cases.

Recognizing the bleed before it becomes significant requires a high index of suspicion as the triad of decreased fetal movement, sinusoidal heart rate, and hydrops fetalis corresponds to a group of symptoms of severe anemia associated with massive fetomaternal hemorrhage. In some situations, such as unexplained stillbirth, persistent maternal perception of decreased fetal activity, hydrops, unexplained elevated middle cerebral artery Doppler, testing for fetomaternal hemorrhage should be considered. Amongst the different diagnostic tests available, the Kleihauer-Betke is a quantitative test based on the principle that hemoglobin F (HbF) is relatively resistant to acid elution compared with the hemoglobin of adult erythrocytes.

When a massive fetal hemorrhage occurs it is crucial to promptly detect it. Immediate cesarean delivery is recommended if the infant is near-term gestation. In cases of preterm gestation, in utero transfusion can be considered to minimize the effects of fetal anemia. If untreated, the effects of fetomaternal hemorrhage can be catastrophic, potentially resulting in cardiac failure, hydrops, hypovolemic shock, intrauterine demise, neonatal death, neurologic injury, cerebral palsy or persistent pulmonary hypertension