Twin-twin transfusion syndrome (TTTS) in pregnancies in which twins share a single placenta (hydrops affects the recipient twin)
Twin anemia-polycythemia sequence (TAPS)
Twin reversed arterial perfusion sequence (TRAPS)
Maternal hyperthyroidism
Fetal cardiac defects and skeletal defects
Noonan syndrome
Mirror syndrome, in which fetal and placental hydrops develops in association with maternal preeclampsia, edema and hypertension
Down syndrome

Diagnosis
Hydrops fetalis can be diagnosed and monitored by ultrasound scans. An official diagnosis is made by identifying excess serous fluid in at least one space (ascites, pleural effusion, of pericardial effusion) accompanied by skin edema (greater than 5 mm thick). A diagnosis can also be made by identifying excess serous fluid in two potential spaces without accompanying edema. Prenatal ultrasound scanning enables early recognition of hydrops fetalis and has been enhanced with the introduction of MCA Doppler. Treatment
The treatment depends on the cause and stage of the pregnancy. Severely anemic fetuses, including those with Rh disease and alpha thalassemia major, can be treated with blood transfusions while still in the womb. This treatment increases the chance that the fetus will survive until birth. Therapy for Cardiac tachyarrhythmia, supraventricular tachycardia, atrial flutter, or atrial fibrillation etiologies are maternal transplacental administration of antiarrhythmic medication(s). This type of treatment is recommended unless the fetus is close to term. Therapy for Fetal anemia caused by a parvovirus infection or fetomaternal hemorrhage is fetal blood sampling followed by intrauterine transfusion. This treatment at an advanced gestational age poses risks and should not be performed if the risks associated with delivery are considered to be less than those associated with the procedure.
Cavernous sinus thrombosis (CST) is the formation of a blood clot within the cavernous sinus, a cavity at the base of the brain which drains deoxygenated blood from the brain back to the heart. This is a rare disorder and can be of two types–septic cavernous thrombosis and aseptic cavernous thrombosis. The most common form is septic cavernous sinus thrombosis. The cause is usually from a spreading infection in the nose, sinuses, ears, or teeth. Staphylococcus aureus and Streptococcus are often the associated bacteria.Cavernous sinus thrombosis symptoms include: decrease or loss of vision, chemosis, exophthalmos (bulging eyes), headaches, and paralysis of the cranial nerves which course through the cavernous sinus. This infection is life-threatening and requires immediate treatment, which usually includes antibiotics and sometimes surgical drainage. Aseptic cavernous sinus thrombosis is usually associated with trauma, dehydration, anemia, and other disorders. Signs and symptoms
The clinical presentation of CST can be varied. Both acute, fulminant disease, and indolent, subacute presentations have been reported in the literature. The most common signs of CST are related to anatomical structures affected within the cavernous sinus, notably cranial nerves III-VI, as well as symptoms resulting from impaired venous drainage from the orbit and eye. Classic presentations are abrupt onset of unilateral periorbital edema, headache, photophobia, and bulging of the eye (exophthalmos).Other common signs and symptoms include:
Ptosis, chemosis, cranial nerve palsies (III, IV, V, VI). Sixth nerve palsy is the most common. Sensory deficits of the ophthalmic and maxillary branch of the fifth nerve are common.