Pregnancy, particularly late pregnancy can impair the clearance of compounds that are metabolized via the microsomal oxidizing pathway or secreted into bile. 

Evidences suggest that although abnormal liver tests is not a common finding in pregnancy, it usually occur in 1 of 10. Researchers have demonstrated that liver metabolic capacity may be diminished in late pregnancy. The analysis of hepatic excretory function in human pregnancy is achieved by both bromosulfophthalein (BSP) and bilirubin tolerance tests.

Additionally, it is evident that the hepatic excretion of both compounds is reduced in the last half of normal human pregnancy.

Moreover, pregnancy can cause a 20% increase in total body water during pregnancy, and cardiac output increases 30% to 50%, which in turn is indicative of shunting of blood to the fetal-placental unit. Serum cholesterol and triglyceride levels starts to rise in the fourth month of pregnancy and peak at term. It has been observed that at term, pregnant women have a 25% to 50% rise in serum cholesterol levels to 265+/-8 mg/dL and a 150% increase in serum triglyceride levels to 180+/-13 mg/dL. Furthermore, chemical evaluation of tissue samples and histologic studies revealed that both cholesterol and triglycerides deposit in the liver during normal pregnancy. Raised levels of triglycerides also indicate a storage pool of metabolic fuel to endure fetus during periods of starvation or insufficient nutrition. However, studies also suggest that both the enlarged gallbladder and supersaturation of bile with cholesterol are responsible for the formation of gallstone in pregnant women.

Source: Medscape Womens Health. 1998 Mar;3(2):2. PMID: 9732096.