Some causes of very elevated levels of ALT include: viral hepatitis, shock, fatty liver of pregnancy, HELLP syndrome, autoimmune hepatitis,

Moderate to mild elevations may be seen with cholestasis, preeclampsia, mononucleosis, hyperemesis gravidarum, alcohol abuse, fatty deposits in the liver, many medicines, chronic liver disease, Wilson's disease, or alpha1-antitrypsin deficiency

References:

Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009 Dec;114(6):1326-31. PMID:19935037
Wallach, J. Interpretation of Diagnostic Tests, Eighth ed. Lippincott Williams & Wilkins, 2007 Fischbach FT, Dunning MB III, eds. A Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia, Lippincott Williams and Wilkins,2004