Hydrops fetalis (nonimmune), also known as fetal hydrops, is a serious fetal condition characterized by the abnormal accumulation of fluid in at least two different areas of the baby’s body. Nonimmune hydrops fetalis is a distinct diagnosis from immune hydrops fetalis, which is characterized by both the abnormal accumulation of fluid in the baby’s body and maternal-fetal blood type incompatibility. Approximately 90% of cases of hydrops fetalis are nonimmunologic, meaning that the cause is not due to maternal-fetal blood type incompatibility. Nonimmune hydrops fetalis has an incidence rate of 1 in 1,500 to 1 in 4,000 live births.
Nonimmune hydrops fetalis can be caused by a wide range of fetal abnormalities. The most common cause of nonimmune hydrops fetalis is a cardiac abnormality, such as atrial septal defect (ASD), tetralogy of Fallot, and ventricular septal defect (VSD), which accounts for 17% to 35% of cases of nonimmune hydrops fetalis.
Chromosomal abnormalities account for 14% to 16% of cases of nonimmune hydrops fetalis, with Turner syndrome, triploidy, trisomy 13, and trisomy 18 being common diagnoses. Hydrops fetalis is also associated with anomalies such as congenital diaphragmatic hernia, encephaloceles, and skeletal dysplasias like achondrogenesis, osteogenesis imperfecta, short-rib polydactyly syndrome, and thanatophoric dysplasia.
Repeat ultrasounds are recommended, as nonimmune hydrops fetalis is frequently associated with the maternal complication preeclampsia. The presence of both hydrops fetalis and preeclampsia is called mirror syndrome.
When hydrops fetalis is suspected, fetal echocardiography, a detailed anatomy ultrasound, maternal serum screening, maternal blood type testing, and fetal karyotype testing are recommended to determine an underlying cause. Nonimmune hydrops fetalis has a fetal mortality rate of 75% to 90%. The perinatal mortality rate ranges from 40-50%, depending on the underlying cause. The mortality rate for babies diagnosed with nonimmune hydrops fetalis and structural heart defects is almost 100%.
The recurrence risk for nonimmune hydrops fetalis depends on the underlying cause. Postmortem examination is recommended in all cases that result in the death of the baby either in pregnancy or after birth.