Step 1: Acute fatty liver of pregnancy (AFLP) is a rare but potentially fatal microvesicular fatty infiltration of the liver linked to disordered fatty-acid oxidation.
Step 2: It characteristically presents late, in the third trimester or the early postpartum period, with nausea, vomiting, jaundice and possible liver failure.
Step 3: Therefore option A, the third trimester, is the best answer. The first trimester, intrapartum period and immediate postpartum are not the typical window for its onset.