Hyperemesis gravidarum (HEG) is a condition with severe nausea and vomiting during pregnancy. It is estimated to occur in 0.3%–3.6% of all pregnancies worldwide [1]. Persistent vomiting resulting in weight loss, nutritional deficiencies, ketonuria, electrolyte imbalance, and dehydration are among the most common reasons for hospital admission in early pregnancy [2]. Many studies have been conducted to understand the etiology and pathogenesis of HEG, but no consensus has been reached on its cause and mechanism [3,4]. Psychological and hormonal changes during pregnancy, thyrotoxicosis, upper gastrointestinal dysmotility, hepatic abnormalities, autonomic nerve dysfunction, nutritional deficiencies, and Helicobacter pylori infection were involved in the etiology [4].

In recent years, inflammation has been related to pregnancy complications, including preeclampsia, intrauterine growth restriction, and spontaneous preterm birth [5]. Many studies have reported that inflammation and oxidative stress are crucial in the pathophysiologic mechanism of HEG and showed that complete blood count parameters could be used as inflammatory markers in these patients [6,7].

A complete blood count test is a part of the routine examination and provides information about the immune system. Hematological parameters such as neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR), mean platelet volume (MPV), platelet distribution width (PDW), plateletcrit (PCT), and red blood cell distribution width (RDW) were examined to indicate inflammation in HEG patients previously [8]. These parameters were combined, and ketonuria and their results were interpreted differently in studies. However, an index called the Systemic Immunity-Inflammation Index (SII), calculated based on peripheral lymphocyte, neutrophil, and platelet counts (neutrophil × platelet/lymphocyte), has not been evaluated in HEG patients previously. This study aimed to investigate the relationship between the blood count parameters, SII, and the degree of ketonuria and determine the importance of these parameters in the severity of HEG.