Association Between Pre-Pregnancy and First-Trimester Hematological Parameters and HELLP Syndrome

To investigate whether hematological biomarkers prior to pregnancy and during the first trimester are associated with subsequent development of HELLP syndrome.

This case-control study was based on laboratory data from 2010 to 2023 in the Copenhagen Capital Region. Pregnant women were identified through first-trimester biochemical screening. A total of 216 women with HELLP syndrome were matched to 4302 controls according to maternal age and date of first-trimester biochemical screening. Hemoglobin, platelet count, and leukocyte count measured one year before pregnancy and during the first trimester were assessed. HELLP syndrome was defined biochemically following national guidelines.

Cases had higher hemoglobin levels before pregnancy (8.5 vs. 8.3 mmol/L, p = 0.04) and lower first-trimester platelet counts (238 vs. 256 × 10⁹/L, p = 0.02) than controls. Hemoglobin levels > 8.5 mmol/L before pregnancy were associated with increased odds of HELLP (OR 2.22, 95% CI 1.15-4.31), whereas hemoglobin levels < 7.5 mmol/L in the first trimester were associated with reduced odds (OR 0.45, 95% CI 0.21-0.96). Lower platelet counts in the first trimester were associated with increased odds of HELLP (OR 0.81 per 25-unit increase, 95% CI 0.69-0.95). No associations were observed for leukocyte counts.

Higher hemoglobin levels before pregnancy were associated with increased odds of HELLP syndrome, whereas lower levels in the first trimester were associated with reduced odds; additionally, lower first trimester platelet counts were associated with increased odds of HELLP syndrome. These findings warrant further studies to evaluate whether hematological biomarkers improve prediction in multivariable HELLP screening models.