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The pathogenesis of intrahepatic cholestasis of pregnancy (ICP) can be related to abnormalities in the metabolism and disposition of sex hormones and/or bile acids, determined by a genetic predisposition interacting with environmental factors. The total amount of oestrogens and progesterone circulating in the blood or excreted in the urine of ICP patients is similar to normal pregnancies. Thus, the search for the cause has been focused on abnormal hormone metabolites. The cholestatic potential of some D-ring oestrogen metabolites is supported by experimental and clinical data. Similar observations with regard to bile acids and progesterone metabolites are still scarce. This article reviews current knowledge in this field, including our own data. Bile acid synthesis appears to be reduced in patients with ICP, in whom primary conjugated bile acids are retained in blood. The major bile acid in blood and urine of these patients is cholic acid instead of chenodeoxycholic acid present in normal pregnancies. Hydroxylation and sulfation of bile acids are enhanced, while glucuronidation appears to be of lesser importance. The synthesis of progesterone appears unimpaired, while the profiles of progesterone metabolites in plasma and urine are different from normal pregnancies, with a larger proportion of mono- and disulfated metabolites, mainly 3alpha,5alpha isomers. Glucuronidated metabolites, however, are unchanged. With the administration of ursodeoxycholic acid (UDCA) to patients with ICP, pruritus and serum liver values are improved, the concentration of bile acids in blood is diminished and the proportion of their conjugated metabolites returned to normal. Simultaneously, the concentration of sulfated progesterone metabolites in blood and their urinary excretion are reduced. The serum levels of bile acids and progesterone metabolites before UDCA administration and their decrease during treatment do not correlate with each other. We propose that patients with ICP have a selective defect in the secretion of sulfated progesterone metabolites into bile and speculate that this may be caused by genetic polymorphism of canalicular transporter(s) for steroid sulfates or their regulation. Interaction with oestrogen metabolites and/or some exogenous compounds may further enhance the process triggering ICP in genetically predisposed individuals.

Intrahepatic cholestasis of pregnancy is characterized by skin pruritus and a biochemical cholestasis of mild to moderate severity appearing during pregnancy (mainly in the third trimester) and disappearing after delivery. It recurs in 40-60% of future pregnancies. The intensity of pruritus and the laboratory alterations (increased serum bile salts and transaminases in almost all patients, hyperbilirubinaemia in 20% of patients) fluctuate during one pregnancy and also vary in subsequent affected pregnancies. This disease has no meaningful consequences for the mother; in contrast, it is associated with an increased risk of foetal distress, causing premature deliveries and stillbirths. Cholestasis of pregnancy has been recognized in most countries and ethnic groups but its prevalence is higher in Chile (14% of deliveries in 1975 and approximately 4% in 1995) and in Sweden than in other countries. The cause in unknown. Sex hormones, mainly oestrogens and progesterone, appear to be involved in its pathogenesis. An interplay between a genetic metabolic predisposition and some environmental factor(s) is apparently relevant. Clinical and experimental studies suggest that a marginal selenium deficiency could be a dietary pathogenic factor. Some drugs attenuate pruritus and improve maternal cholestasis, but not the foetal prognosis. Ursodeoxycholic acid (UDCA) administration provides a significant improvement in maternal pruritus and in the biochemical abnormalities, with no adverse effects in the mother or child. Recent clinical and experimental studies show that UDCA administration improves maternal disease and foetal prognosis without any detectable adverse effects.