Intrahepatic cholestasis (ICP) is one of the most frequent hepatopathies during pregnancy; it occurs in the second/third trimester and resolves for the mother after delivery. However, for the fetus it can lead to increased risks, such as respiratory distress syndrome, preterm delivery, stillbirth or even intrauterine death by asphyxia [1,2]. ICP is defined by the presence of nocturnal palmo-plantar pruritus, elevation of maternal serum total bile acids (TBA), >10 μmol/L, and could be accompanied by increased liver enzymes and bilirubin levels indicating liver dysfunction [3]. ICP has a prevalence of ≤ 1% to 27% of pregnancies around the world, its prevalence is high in Latin America, being up to 5 - 27% in Chile [2,4]; however, in Mexico, it has not been determined [1].

The main risk factors for ICP are maternal age >35 years, history of biliary pathology, or ICP in previous pregnancies, diabetes mellitus, viral hepatitis B or C, tobacco use, multiple pregnancies and use of assisted reproductive technology [5,6]. Overweight and obesity are well-known risk factors for several pregnancy-related complications as gestational diabetes mellitus (GDM) or preeclampsia (PE) [7]. However, research about the implications of maternal body mass index (BMI), in particular obesity, on the development of ICP is scarce, and the reported data are inconclusive [7,8].

ICP is caused by an alteration of liver function due to the elevation and accumulation of bile acids (BA), and as a consequence, their elevation in maternal serum. They are inherently cytotoxic and thus their metabolite is tightly regulated. In ICP, the flow of bile salts from the liver to gallbladder is disrupted and there is a compensatory transport of liver bile salts into the bloodstream [9].

The etiology of ICP is multifactorial, involving genetic, hormonal, immunological and environmental factors, such as genetic variants of bile acids transporter proteins; elevated estradiol and sulfated metabolites of progesterone that modifies the estradiol-bile acid axis [4,10]. Immunological modifications are primary to cholestasis because ICP is an inflammatory disorder. Imbalance of immune function may destroy the immune microenvironment of pregnant women, leading to various pathological reactions as a response of T helper cells with an increase of cytokines such as tumor necrosis factor alpha (TNF-α) [10,11] .

TNF-α is important factor needed for the growth of the fetus and placenta but can be lethal when expressed in very high levels. In ICP, the significant increase comes from placenta production. These changes are related to down regulation of bile salt export pump and trophoblast apoptosis [11].

The placenta is an important and understudied organ in ICP, impairment of feto-maternal transport and lesions in the placental structure have been reported, bile acids also induced vasoconstriction [12] and increased cell apoptosis and intracellular edema due of decreased cell surface death receptor ligand (FASL) expression and an increased expression of the FAS receptor in the syncytiotrophoblast, induced by TNF-α and interferon gamma (IFN-γ) [11]. Comparison of placental lesions between patients with ICP and healthy patients has been performed in previous studies, but no statistically significant differences were found [12,13]. However, Geenes, et. al., identified small chorionic villi for gestational age, dense fibrotic stroma, congestion of the villi and an increased number of syncytial knots, which were reproduced in an in vitro model of liver cholestasis [14]

The aim of this study was to assess the histopathological features of the placenta of women diagnosed with ICP, and to determine if specific lesions are associated with liver function alterations or with the comorbidities present in ICP women, particularly in relation to overweight and obesity.

Preterm delivery and cesarian resolution of pregnancy have been previously associated with intrahepatic cholestasis, but not with overweight and obesity. The present study supports and extends these observations [7,8]. More than 50% of ICP women had preterm delivery, which could be explained by the therapeutical indication to avoid increased risk of stillbirth in ICP patients. Indeed, the induction of labor is often recommended at 37 weeks of gestation to balance the risk of iatrogenic preterm delivery against the risk of fetal mortality [3,4,18]. Besides, there is a markedly increased risk of stillbirth when bile acid levels are ≥100 μmol/L [3,17] and delivery in these cases may be considered at an earlier gestational age, such as 35 to 37 weeks; however, these decisions should be individualized with careful patient counseling [3,5,18].

A previous study showed that placentas of ICP patients present morphological alterations such as increased terminal villous and capillary surface area, and number of syncytial knots [17]. In addition to the lesions reported in that study, we also found decidual arteriopathy, intervillous fibrin, delayed villous maturation and chorangiosis as the most frequent lesions in placentas of ICP patients, probably due to the different methodology employed for the analysis. Interestingly, chorangiosis was more frequent and AVM without ISK was reduced in ICP patients with normal weight (Table 3).

In our cohort study, 70% of the patient presented body weight alterations and 48.47% had other comorbidities as PE, GDM or hepatic alterations (Table 3). Overweight and obesity have not been directly associated with intrahepatic cholestasis [7]; however, we could not exclude a direct effect of metabolic changes generating ICP as reported for gestational diabetes or preeclampsia [7], and recently, an increased incidence of ICP was associated with a direct linear increment of BMI [8,19]. The obesity prevalence in Mexican women has increased dramatically by 30.6 %, from 2000 to 2018; thus presently, more than 75 % of women on reproductive age have a BMI above 25 kg/m2, and the number of women who are expected to have obesity (BMI ≥ 30 kg/m2) when they become pregnant is unknown, but near 36% of women between 20 to 50 years old exhibit obesity [20]. However, in the present study patients with obesity (38.1%) correspond to the expect frequency of the obese women, and whether obesity may contribute directly to the development of ICP deserves to be further explored. Nevertheless, its effect in the development of PE, GDM and other hepatopathies is clearly appreciated in the group of the obese women as 67.5% showed comorbidities (Table 3).

Previous studies performed with placental explants from ICP patients and in rodent models, have reported that the excess of BA produces vasoconstriction with a consequently decreasing volume of blood flow, generating a hypoxic environment that directly affects the structure of the placenta, being AVM with ISK the most representative lesions [14]. In our study, we did not find any association between BA increased levels and placental lesions; however, AVM with ISK was the most frequent lesion in our ICP cohort, although more studies are needed to correlate these findings with TBA levels.

It has been reported that in ICP the activation of endoplasmic reticulum stress (ERS), enhanced apoptosis of the trophoblasts in the placenta and deoxycholic acid can induce a significant increase in the expressions of ERS markers, thus leading to trophoblast apoptosis, suggesting that this ERS-induced phenomena may play a key role in the development of ICP [21].

Many other histopathological alterations in the placenta were observed in patients with ICP, as is depicted in Table 2. However, these lesions have not been associated previously with pregnancy hepatic alterations. DVM has been associated mainly with chronic hypoxia [22] and more frequently, with metabolic diseases such as GDM [23]. However, further studies are needed to determine whether DVM is a lesion associated with metabolic disturbances in ICP patients and liver dysfunction.

Interestingly, chorangiosis was found in 26.05% of the ICP studied placentas, this lesion is due to a marked increase in the number of vessels (>10 capillaries in more than 10 villi in several areas) from non-infarcted and non-ischemic placental areas [24,25]. It has been suggested that chorangiosis is a compensatory response to chronic hypoxia, associated with different comorbidities including GDM and PE, to allow vascular remodeling to adapt to low oxygen conditions [26]. Chorangiosis also has been reported as a hallmark of DVM in placentas from obese pregnancies due to insulin resistance and hypoxia [24]; DVM was present in 22.68% of the placentas in our study. However, chorangiosis has not been previously reported as characteristic of ICP. Interestingly, it was more frequent in the normal weight group, maybe do to a more efficient compensatory mechanism as has been reported for pregnancies with obesity, GDM, DM1 and those at high altitudes [25,27].

Studies related to placental histopathology during ICP, are scarce, and to the best of our knowledge, only one previous, non-recent study reported a relation of ICP with placental lesions. Here, we demonstrated that other type of lesions might be present in placentas of patients with ICP. In this study, increased levels of bile acids and liver enzymes did not correlate with specific placental damage. Interestingly, chorangiosis and AVM without ISK were increased and reduced respectively in ICP patients with normal weight in contrast with obese and overweight patients. Thus, this study supports and extends the idea that ICP might be related to placental lesions, although, further studies are needed to determine if there is an association between ICP and specific placental lesions. Regarding the treatment of ICP with UDCA, additional therapeutic strategies should be considered, since it was observed that a reduced number of patients responded to UDCA treatment.

All authors have made substantial contributions as follows: (1) the conception and design of the study, or acquisition of data, or analysis and interpretation of data, (2) drafting the article or revising it critically for important intellectual content, (3) all authors gave their approval for the final submitted version.