Hemolysis, elevated liver enzymes, and low platelet count syndrome (HELLP syndrome), first named by Weinstein [1] in 1982, is a severe complication of preeclampsia characterized by hemolysis (H), elevated liver enzymes (EL), and low platelet count (LP). The incidence of HELLP syndrome is approximately 0.2%–0.8% [2]. It is a multisystemic disease with complications including liver and kidney insufficiency, thrombosis, eclampsia, and postpartum hemorrhage. In addition to these maternal complications, HELLP syndrome can result in preterm birth, fetal growth restriction, and placental abruption, significantly affecting fetal health. The maternal mortality rate is approximately 9.7%, with neonatal mortality reaching 37% [3]. Thus, HELLP syndrome poses a grave threat to the lives of both mothers and infants.

The specific diagnostic laboratory values for HELLP syndrome vary across countries and regions [4]. However, many physicians assess disease severity based on three main criteria. Complete HELLP syndrome is defined by the presence of all three criteria, whereas partial HELLP syndrome is diagnosed when one or two criteria are met [5]. Aydin et al. [6] suggested that complete and partial HELLP syndromes may represent a continuum in the natural progression of the disease. The debate continues regarding whether partial and complete HELLP syndromes constitute a continuum of the same condition or represent distinct conditions. The pathogenesis of HELLP syndrome remains unclear. Enhancing awareness of this condition is crucial for reducing maternal and infant mortality. This article reviews the clinical features of partial and complete HELLP syndromes to strengthen understanding and management of the condition and improve perinatal outcomes.

The specific pathogenesis of HELLP syndrome remains unclear. Petca et al. [2] demonstrated that approximately 70%–80% of HELLP syndrome cases are secondary to preeclampsia. As a serious complication of preeclampsia, the main pathological changes are consistent with those seen in preeclampsia [7], such as vasospasm and reduced organ perfusion; however, the underlying mechanism of HELLP syndrome development remains unclear. The inflammatory immune system is abnormally activated in HELLP syndrome [8]. Some studies have found that patients with HELLP syndrome have a higher neutrophil-to-lymphocyte ratio and a lower platelet-to-lymphocyte ratio due to an increase in neutrophils in peripheral blood samples [9, 10]. One study discovered that neutrophil extracellular traps promote endothelial cell activation and further increase the risk of thrombosis through the action of interleukin-1a (IL-1a) and cathepsin G [11]. This may be related to infection status; however, the specific causes remain unknown. In this study, patients with HELLP exhibited abnormal white blood cell counts, with the complete HELLP group showing higher white blood cell counts. Inflammation has been speculated as a potential cause of HELLP syndrome. However, due to limited data, experimental results related to neutrophils, monocytes, immune cells, and complement in white blood cells were not addressed in this study and require further investigation.

HELLP syndrome is believed to result from multiple factors, pathways, and mechanisms [12]. The annual delivery count at Wuxi Maternal and Child Health Hospital is approximately 10,000, with the incidence of HELLP syndrome estimated at 0.1%. Advanced age is a key risk factor for HELLP syndrome [13]. In this study, 23 patients (23.9%) were aged over 35 years, and the average age of the 96 pregnant women was 30.7 years, higher than the optimal childbearing age recommended by the National Health Commission. Obesity (BMI $\ge$30 kg/m²) is a known risk factor for HELLP syndrome or preeclampsia [14]. In this study, the obesity rate in patients with HELLP was 18%, and excessive BMI during pregnancy should raise concern. A family history of hypertension is also an important risk factor for HELLP syndrome. In this study, 19 patients had a family history of hypertension, including 13 in the partial HELLP group and 6 in the complete HELLP group. The family history of hypertension was consistent with reports in the literature [15]. Patients with HELLP syndrome may also present with other conditions. This study found that approximately 27% of patients with HELLP syndrome had gestational diabetes, with the rate of gestational diabetes in the partial and complete HELLP groups ranging from 26% to 27%, showing no significant difference. Both gestational diabetes mellitus and gestational hypertension can impair vascular endothelial cell function, leading to microvascular damage and organ complications, such as kidney and retinal damage. The interaction between these two conditions poses a significant threat to the health of both the mother and fetus [16, 17]. Therefore, when preeclampsia is accompanied by gestational diabetes, early intervention and monitoring of disease progression are essential to prevent HELLP syndrome. This analysis found no differences between patients with partial and complete HELLP regarding general age, gestational body mass index, family history of hypertension, history of preeclampsia, or pregnancy complications such as gestational diabetes mellitus.

Typical symptoms of HELLP syndrome include general discomfort, right upper abdominal pain, and increased pulse pressure difference. However, these symptoms are non-specific [18]. Some pregnant women may experience nausea, vomiting, and other gastrointestinal symptoms, which are difficult to identify. Hypertension and proteinuria are not typical features of HELLP syndrome [19]. Therefore, diagnosis primarily relies on laboratory tests [18]. The examination indicators were divided into two categories: diagnostic and non-diagnostic indicators of HELLP syndrome. Based on the grouping definitions, the two groups exhibited differences in ALT, AST, LDH, TBil, and platelet counts, with the complete HELLP group presenting more severe values. However, the white blood cell count and D-dimer levels in the complete HELLP group were significantly higher than those in the partial HELLP group. This suggests that patients with preeclampsia and concurrent inflammation or hypercoagulability are more likely to develop complete HELLP syndrome. The strong reserve capacity of the kidneys makes the increase in serum creatinine (Scr) less apparent in early renal injury; when Scr levels rise, it often indicates severe kidney damage [20]. While not a prerequisite for diagnosing HELLP syndrome, this study identified 11 patients with Scr $>$90 µmol/L, accounting for 11.4%. This highlights the importance of monitoring renal function during the diagnosis and treatment of HELLP syndrome to protect kidney health.

Pregnancy termination is recommended for patients with HELLP syndrome. Severe preeclampsia and HELLP syndrome are not absolute contraindications for vaginal delivery, and the method of delivery should be based on the patient’s condition and preferences. In this study, most pregnant women underwent cesarean section for pregnancy termination, while two patients with milder conditions opted for vaginal delivery. Both newborns survived without asphyxiation. Following active treatment measures, both women were discharged within four to five days after delivery.

HELLP syndrome can result in significant adverse pregnancy outcomes and poses a threat to maternal health. Eclampsia represents the most severe stage in the progression of hypertensive disorders during pregnancy and is characterized by convulsions that occur in preeclampsia. In this study, five women with HELLP syndrome experienced convulsions, which led to fetal demise in two cases. Among these five patients, two had convulsions before admission to the hospital and were transported to the emergency room by ambulance. Three women had antenatal convulsions, while two developed postpartum eclampsia, indicating that even after delivery termination, there remains a possibility of disease exacerbation or the occurrence of eclamptic episodes. Therefore, clinicians should remain vigilant during clinical diagnosis and treatment. This phenomenon may be attributed to the increased vulnerability of the brain and kidneys to persistent vascular endothelial dysfunction after childbirth [21]. Notably, there were no maternal deaths among the HELLP syndrome cases collected in this study from 2016 to 2023, which can be attributed to the extensive experience in emergency and critical care among clinicians at our hospital and the support and cooperation of the multidisciplinary team.

Patients with HELLP syndrome are susceptible to fetal growth restriction, perinatal asphyxia, and other complications, including systemic small artery constriction, high placental vascular resistance, and placental tissue ischemia [13]. Thirteen perinatal deaths occurred during the study period. The mean maternal arterial pressure of the fetuses who died was 137 mmHg, compared to 122 mmHg for the surviving fetuses. In terms of gestational age, eight of the 13 pregnant women were between 28 and 34 weeks of gestation. During pregnancy, particularly between 28 and 34 weeks, patients with preeclampsia should closely monitor their blood pressure and receive appropriate medical treatment under supervision.

The strength of our study lies in evaluating the outcomes associated with complete and partial HELLP syndrome using data collected from a single tertiary care medical center, where consistent protocols were followed for managing HELLP syndrome. Future studies may involve collaboration with hospitals in other regions to expand the study to multiple obstetric medical centers, which would enhance the generalizability of the results.

Partial and complete HELLP syndromes differ primarily in laboratory indices, but they exhibit similarities in general characteristics, pregnancy-related complications, other laboratory tests, and neonatal demographic features. Both conditions can result in severe perinatal outcomes. Clinical diagnosis and treatment do not require the simultaneous presence of all three indicators—hemolysis, elevated liver enzymes, and low platelet count. Partial HELLP syndrome should be considered, and timely clinical treatment and intervention are essential.

BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; MAP, mean arterial pressure; IVF-ET, in vitro fertilization-embryo transfer; ALT, alanine aminotransferase; AST, aspartate aminotransferase; LDH, lactate dehydrogenase; TBil, total bilirubin; PLT, platelet; Scr, serum creatinine; BUN, blood urea nitrogen; Fib, fibrinogen; FGR, fetal growth restriction.

Data is provided within the manuscript. All data in this paper are from the medical database of Wuxi Maternal and Child Health Hospital. To protect patient privacy, the specific data involved in this study is not publicly available. All data are available upon reasonable request from the corresponding author.

HG designed the research study and analyzed the data. JYC collected the data. HQW designed the research study. MHJ and YG provided help and advice on the data collection and ethics application. YLF designed the work, reviewed the article, and provided financial support. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

This study was performed in accordance with the Declaration of Helsinki and was reviewed and approved by the Ethics committee of the Wuxi Maternal and Child Health Hospital (No. 2024-06-0507-14). This is a retrospective research paper, and the article does not show any clinical details or images that may infer the identity of patients. All participants provided informed consent.

This study was supported by the following funding sources: Jiangsu Maternal and Child Health Research Project (F202135); Project of Women’s Health Care Department under the Key Disciplines of Maternal and Child Health Care in Jiangsu Province (SFY3-FB2021).

The authors declare no conflict of interest.

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