Reference Intervals for Common Biochemistry and Hematology Parameters in Early Pregnancy-A Prospective Study

Background: The aim of this study was the determination of reference values for the common laboratory parameters in early pregnancy using a direct method and to assess their clinically significant difference, which was compared to the reference intervals for non-pregnant women with respect to the reference change value (RCV). Methods: This study was conducted from September 2022 to December 2023 at the Clinical Department of Laboratory Diagnostics, Clinical Hospital Centre RIJEKA, Croatia. The inclusion criteria were as follows: age ≥ 18 years, singleton pregnancy, normal ultrasound examination, and prenatal screening. The exclusion criteria were as follows: recent illness, pregnancy-related complications, medically assisted reproduction, and medication use. The reference intervals were established using the non-parametric percentile method according to the CLSI EP28-A3c recommendation. The reference values were compared to those of non-pregnant women and judged against RCV values based on biological variation. Additionally, we tested the influence of food consumption and oral supplements. Results: The data of 299 participants were included in the study. Laboratory tests whose changes are clinically relevant lower in early pregnancy are as follows: hemoglobin, MCV, hematocrit, MCH, urea, creatinine, albumin, alkaline phosphatase, lactate dehydrogenase, sodium, and magnesium. The clinically relevant higher values are as follows: RDW, total leukocyte count, neutrophil granulocytes, monocytes, CRP, total cholesterol, triglycerides, and amylase. UIBC has a wider reference range. The consumption of food and supplements has no clinically significant influence in relation to the RCV. Conclusions: Establishing reference intervals in pregnancy remains a challenge due to the metabolic changes during pregnancy, as well as its clinical significance.