Pregnancy, due to the hyperestrogenic state and pregnancy-specific hemodynamic changes, predisposes to liver diseases. Pregnancy-specific liver dysfunctions include hyperemesis gravidarum (HEG), intrahepatic cholestasis of pregnancy (ICP), hepatic infarction, acute fatty liver of pregnancy, hepatic rupture, and hemolysis, elevated liver enzymes, and low platelet (HELLP) syndrome associated with preeclampsia. Liver disorders are characterized by elevated liver enzymes [1]. HEG is defined as persistent and excessive vomiting that begins before the 22nd week of pregnancy, typically occurring in the first-trimester. Symptoms typically begin around 6 to 8 weeks of gestation and may persist throughout the pregnancy. Approximately 50% of women diagnosed with HEG have serum aminotransferase levels that are up to twice the upper limit of normal [2]. HEG occurs in approximately 0.3% to 3% of pregnancies [3]. Mild jaundice is rarely observed in patients with HEG, and bilirubin levels can rise to 4 mg/dL. Alanine aminotransferase (ALT) levels have been found to be higher than those of aspartate aminotransferase (AST) [4, 5].

Another liver pathology associated with pregnancy is ICP, which is characterized by decreased bile flow due to impaired hepatocellular secretion or obstruction of intrahepatic bile ducts. ICP typically begins in the late second-trimester and is associated with significant fetal complications, such as premature birth, neonatal respiratory distress, fetal distress, and stillbirth. The incidence of ICP varies significantly, ranging from 0.05% to 2.76%, depending on factors such as ethnicity and geographic region; however, its etiology remains not fully understood [6, 7]. The diagnosis of ICP is based on unexplained itching during pregnancy, increased serum total bile acid levels, and abnormal liver function tests [8]. An increase in serum total bile acids (TBA) is the primary biochemical marker for ICP and is present in more than 90% of affected pregnancies. Levels above 10 µmol/L are considered diagnostic and represent the first laboratory abnormality [9, 10, 11].

AST and ALT are produced in hepatocytes and serve as important markers used to determine the degree of liver damage. AST is found as both cytosolic and mitochondrial isoenzyme and is present in the myocardium, skeletal muscle, kidneys, brain, pancreas, lungs, leukocytes, and red blood cells outside the liver. ALT is a cytosolic enzyme found exclusively in the liver and is higher than AST in liver-specific diseases [12]. AST and ALT levels rise in about 60% of cases, typically remaining below twice the upper limit of normal, but they can reach exceed above 1000 U/L, making differentiation from viral hepatitis essential [13]. Bilirubin is a toxic substance resulting from the breakdown of erythrocytes [14]. If bilirubin is not processed and excreted from the body due to liver damage, its levels increase in the blood. However, these markers cannot be determined through routine prenatal examinations and tests.

Defining measurable values in routine examinations is valuable for predicting or diagnosing cholestasis in early pregnancy. Rapid clinical evaluation is critical for differentiating pregnancy-specific liver diseases from non-pregnancy-related pathologies, ensuring timely and appropriate treatment, and reducing maternal and fetal risks. Although HEG and ICP are liver pathologies associated with pregnancy, their onset times are distinctly different. In our study, we investigated whether HEG, which is specific to the early stages of pregnancy, can predict the occurrence of ICP in the later weeks of pregnancy.

The demographic data of the 72 patients diagnosed with ICP included in the study are listed in Table 1.

In pregnant women diagnosed with ICP, there was no significant difference in gestational age between the groups with and without a history of HEG (p $>$ 0.05). In pregnant women diagnosed with ICP, there was no significant difference in AST, ALT, alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), and direct bilirubin values between the groups with and without a history of HEG (p $>$ 0.05). However, the total bilirubin and indirect bilirubin levels were significantly lower in the group with a history of HEG compared to the group without a history of HEG (p 0.05). Lastly, the TBA levels were significantly higher in the group with a history of HEG compared to the group without a history of HEG (p 0.05) (Table 2).

In our study, patients with a history of HEG diagnosed with ICP in the third trimester were compared to a control group without a history of HEG. Furthermore, total bilirubin and indirect bilirubin levels were found to be significantly lower, while TBA levels were found to be significantly higher compared to the control group.

Current studies are evaluating AST-platelet ratio (APRI) as a predictor of ICP [16, 17, 18, 19]. In the study conducted by Gok et al. [16] in 2023, the effects of ALT, AST, platelet count, and APRI on predicting ICP were examined. The first-trimester APRI, AST, and ALT levels, were found to be statistically significantly higher than the control group, while the platelet count was found to be significantly lower in the study group, despite remaining within the normal reference range [16].

In the studies conducted by Tolunay et al. [17] in 2021 and Saadi et al. [18] in 2024, the predictive value of APRI score for ICP was investigated. Both studies found that patients with ICP had significantly higher first-trimester APRI scores compared to controls, and a significant positive association was observed between first-trimester APRI scores and third-trimester fasting bile acid levels in women with ICP [17, 18].

In the case-control study conducted by Peker et al. [19] in 2024, it was observed that APRI scores were statistically higher in patients with ICP who experienced composite adverse outcomes in all trimesters.

In 2023, Sun et al. [20] conducted a comparative analysis of plasma cell-free RNA (cfRNA) in patients with ICP, hepatitis B virus (HBV), and healthy pregnant women. They identified changes in plasma cfRNA during early pregnancy related to the pathophysiology of ICP. These changes were found to differ between patients diagnosed with ICP in the early and late stages. The authors reported that plasma cfRNAs could serve as a non-invasive diagnostic tool for the early identification of women at risk for ICP during pregnancy [20].

Zhang et al. [21] conducted a retrospective study to predict ICP within the first 20 weeks of gestation, comparing pregnant women diagnosed with ICP to a control group of healthy pregnant women. As a result of the study, they found elevated levels of large platelet ratio, AST, GGT, and fibrinogen in the patients, alongside reduced levels of activated partial thromboplastin time and mean corpuscular hemoglobin concentration. In contrast, our study showed no differences in AST and GGT values between the case and control groups. Total bilirubin and indirect bilirubin values were found to be significantly lower in patients with ICP who had a history of HEG [21]. The study found that low serum bilirubin levels were associated with significantly increased odds of developing metabolic syndrome [22]. Decreased serum bilirubin concentrations are associated with an increased risk of various atherosclerotic diseases. On the other hand, bilirubin levels are inversely associated with cardiovascular risk factors, including body mass index (in obesity), cholesterol levels, and blood sugar levels (in type 2 diabetes) [23].

In a study by Hançerlioğullari et al. [24] in 2015, the authors analyzed pregnancy-associated plasma protein A (PAPP-A) and free beta-human chorionic gonadotropin (beta-hCG) levels obtained from biochemical evaluations in the first-trimester to predict cholestasis in patients diagnosed with ICP. The first-trimester PAPP-A levels were found to be significantly lower in the group diagnosed with ICP compared to the control group [24].

Dong et al. [25] examined acyl-CoA oxidase 1 (ACOX1), L-palmitoylcarnitine, and glycolic acid in placental tissue and serum during the first- and second-trimesters to predict ICP. They found elevated levels of these substances in ICP patients during the first-, second-, and third-trimesters, suggesting that ICP could be detected early [25].

Yurtcu et al. [26] proposed the use of biomarkers, including leptin, apelin, adiponectin, and ghrelin, to predict and diagnose ICP. Li et al. [27] conducted a case-control study using placental growth factor (PIGF), total cholesterol (TC), and triglycerides (TG) levels to predict ICP. Eyisoy et al. [28] found that patients with ICP exhibited higher APRI scores compared to those with mild ICP, reporting a significant positive relationship between APRI scores and TBA. In our study, we also observed elevated TBA levels in women with a history of HEG and ICP [28].

In a cohort study by Marschall et al. [29], known prior hepatobiliary diseases, especially cholelithiasis, chronic hepatitis, and hepatitis C (HCV), were found to increase the risk for ICP. Similarly, another study by Wijarnpreecha et al. [30] indicated that HCV also increased the risk of ICP. Similarly, in our study, we examined whether HEG, a condition affecting the liver, could serve as a predictor for ICP, thereby contributing to the existing literature.

Despite the research conducted, the exact causes of ICP remain unknown, and early predictive biomarkers for ICP are still not available. Our literature review did not identify any studies on this subject. While some studies on predicting ICP exist, as we mentioned in our discussion, our study differs in that we specifically examined the serum TBA and liver function tests (LFT) in pregnant women with ICP who also have a history of HEG [24, 25, 26]. It is possible that patients with HEG may have undiagnosed subclinical liver disease, which could lead to isolated enzyme elevations in liver enzymes. This issue could be addressed by a comprehensive study that monitors LFT before and after the onset of HEG.

To the best of our knowledge, no such study has been conducted to date. We hope that this will be the first study in the literature, contributing to the evaluation of ICP patients through different approaches. The direct and indirect bilirubin levels in serum or urine are elevated in approximately 25% of women but are lower compared to those seen in other cholestatic diseases [31]. We believe that pregnant women with a history of HEG and ICP may face an increased risk of metabolic diseases in the future.

In this study, it was found that the TBA levels were higher in pregnant women with ICP who had a history of HEG when compared to those with ICP without a history of HEG. Based on these results, it is recommended that patients with a history of severe HEG be monitored more closely in the later stages of pregnancy for ICP. In pregnant women with ICP and a history of HEG, total bilirubin and indirect bilirubin were found to be low. This finding suggests the need for careful attention to potential liver damage. However, larger sample sizes and more comprehensive studies are needed to confirm these results.

The data sets used and analyzed during the current study are available from the corresponding author on reasonable request.

AKK designed the research study, analyzed and interpreted the data. SAK and AKK performed the research. SAK was involved in the drafting of the manuscript. Both authors contributed to editorial changes in the manuscript. Both authors read and approved the final manuscript. Both authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

The study was conducted in accordance with the Declaration of Helsinki. The study was conducted in accordance with the Declaration of Helsinki. Patient privacy and data confidentiality were guaranteed, and approval was obtained from the ethics committee to waive informed consent because the study consisted of information obtained retrospectively from hospital electronic records. Ethic Approval was obtained from the Non-Interventional Clinical Research Ethics Committee of Istanbul Training and Research Hospital with decision number 187 dated 21.07.2023.

This research received no external funding.

The authors declare no conflict of interest.