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What is A pregnant female presents with fever. On lab investigation her Hb was decreased (7 mg%), TLC was normal and platelet count was also decreased. Peripheral smear shows fragmented RBCs. Which is least probable diagnosis? and explain in detail?
The clinical scenario of the patient shows the following signs and symptoms:

Fever
Anemia
Thrombocytopenia
Normal total leukocyte count
Fragmented RBCs (Schistocytes) on peripheral smear.

Now let us review each option one by one
Option (a): DIC 
Harrison 20/e, p 979

DIC may present with sudden onset of fever (as the M/c cause of D/c is sepsis)
Excessive bleeding may lead to anemia
Platelet consumption may lead to thrombocytopenia
Leukocyte count is not affected
Intravascular microangiopathic hemolysis can lead to schistocytes on peripheral smear.

Williams Obs 23/e, p 786
Option (b): TTP i.e Thrombotic thrombocytopenic purpura.
TTP presents with a pentad of:

Fever
Microangiopathic haemolytic anemia, leading to anemia and fragmentation of RBCs
Thrombocytopenia
Neurologic symptoms
Renal failure.

Option (c): HELLP syndrome
HELLP syndrome presents with the combination of:

Hemolysis because of which fragmented RBC’s may be seen
Elevated liver enzymes and
Low platelet count
Fever may or may not be present.

Oprion (d): Evans syndrome
Hoffman: Hematology: Basic Principle and Practice, 5/e

Evans syndrome is an autoimmune disease in which an individual’s antibodies attack their own red blood cells and platelets.
Its overall pathology resembles a combination of autoimmune haemolytic anemia and idiopathic thrombocytopenic purpura.
Autoimmune hemolysis leads to the formation of spherocytes and not schistocytes.
Schistocytes are fragmented RBCs that are the result of microangiopathic hemolysis.
Autoiminune destruction of RBCs leads to the formation of spherocytes.

Hence, Evans syndrome is the least likely possibility in this clinical scenario.