Types of studies and patients
The eligibility criteria for the inclusion of studies were predetermined. Observational studies that assessed differences in serum LDH levels among women with hypertensive disorders of pregnancy (gestational hypertension, preeclampsia, eclampsia, HELLP syndrome) and healthy controls were considered eligible for inclusion. Small case series (<10 patients), case reports, conference proceedings and animal studies were excluded from the present systematic review. Studies that involved pregnant women with comorbidities were excluded from the present systematic review. The control group consisted of healthy pregnant women, without evidence of any gestational complication. Studies were not excluded based on preeclampsia definition, since no date restrictions were applied.