Introduction

• Cause: likely caused by a combination of fetal and maternal factors.
• Signs: bilateral ventral abdominal distension.
• Diagnosis: clinical signs, rectal examination, ultrasonography and/or allantocentesis.
• Treatment: supportive care, induction of labor, elective cesarean section, percutaneous or trans-cervical drainage of allantoic fluid or euthanasai.
• Prognosis: poor to guarded.

Pathogenesis

Etiology

• Placental abnormality, in particular of the maternal caruncles.
• Likely caused by a combination of fetal and maternal factors.
• Concurrent fetal abnormalities are reported, but their role in the etiology is not fully understood. Such abnormalities include cleft palate, pituitary hypoplasia and bulldog calf syndrome and fetal polyuria.
• Also described in association with IVF-induced large offspring syndrome.

Pathophysiology

• Placentomes often show degenerative changes, and there may be placental edema.
• Allantoic fluid volume can be 10x normal, ie up to about 200 l.
• Hydrops allantois and hydrops amnion may occur concurrently (about 5% of cases).

Timecourse

• Fluid accumulation is relatively rapid over just a few weeks, typically from mid-gestation onwards.

Epidemiology

• Tends to occur sporadically, with occasional clustering in a herd.
• Estimated to affect about 1 in 7,500-10,000 gestations.
• Hydrops allantois is 9-15 times more common than hydrops amnion.

Diagnosis

Treatment

Prevention

Outcomes