A 9 month old pregnant lady presents with jaundice and distension, pedal edema after delivering normal baby. Her clinical condition deteriorates with increasing abdominal distension and severe ascites. Her bilirubin is 5 mg/dl, S. alkaline phosphatase was 450u/L and ALT (345lu). There is tender hepatomegaly 6cm below costal margin and ascetic fluid show protein less than 2 mg% Diagnosis is:
The most common causes of acute severe liver injury in a young pregnant women are:

Viral hepatitis (HAV, HBV)
Eclampsia, preeclampsia (HELLP syndrome)
Acute fatty liver of pregnancy
Budd-Chiari syndrome.

Let us discuss each option separately
Preeclampsia and eclampsia/HELLP syndrome:

It is the most common cause of abnormal liver function test in women.
Amniotransferases are modestly elevated.
But in these cases delivery of the fetus is followed by rapid normalization of the hepatic abnormalities.
Moreover the question does not mention any history of PIH, hemolysis and thrombocytopenia (HELLP syndrome).

Acute fatty liver of pregnancy:

Acute fatty liver develops in the third trimester.
Jaundice develops a few days after the onset. The serum bilirubin is rarely above 10 mg/dL.
Alkaline phosphate is markedly elevated.
Aminotransferases are moderately elevated.
A markedly raised serum ammonia is the most diagnostic finding in establishing the diagnosis of acute fatty liver of pregnancy and symptoms rapidly abate with parturition in most patients.

Fulminant hepatic failure:

The patient presents with features of severe acute hepatitis leading to the development of hepatic encephalopathy within 8 weeks of onset.
The bilirubin increases to 20-30 mg/dL.
The aminotransferase levels are very high (>1000)
Alkaline phosphatase moderately elevated.
Delivery is usually the best treatment.

Budd-Chiari syndrome:

It is a disorder characterized by thrombotic occlusion of the hepatitis veins.
It is a rare complication of pregnancy.
Most of the cases presents within few weeks of delivery but in several cases onset occurs during pregnancy.
Clinical triad of Budd-Chiari syndrome includes sudden onset of abdominal pain, hepatomegaly and ascites (ascites with high protein content is almost always present) near term or shortly after delivery.
Tender hepatomegaly is one of the hallmark of Budd-Chiari syndrome.
Aminotransferases are mildly elevated.
Jaundice is seen in only half of the cases.
Acute fatty liver of pregnancy
HELLP syndrome
Acute fulminant, liver failure
Budd chiari syndrome