Pregnancy-Specific Reference Intervals for Maternal Hematologic and Biochemical Parameters in Japanese Twin...

To establish clinically applicable reference intervals for complete blood count (CBC) and key biochemical parameters in a Japanese cohort of twin pregnancies and to compare these parameters with singleton pregnancies.

This retrospective cohort study included women with twin pregnancies who delivered at a Japanese perinatal center between 2013 and 2023. CBC parameters (white blood cell count [WBC], red blood cell count [RBC], hemoglobin [Hb], hematocrit [Ht], mean corpuscular volume [MCV], mean corpuscular hemoglobin [MCH], mean corpuscular hemoglobin concentration [MCHC], and platelet count [PLT]) and biochemical markers (plasma glucose, aspartate aminotransferase [AST], alanine aminotransferase [ALT], triglycerides [TG], total cholesterol [TC], and uric acid [UA]) were evaluated. Measurements were categorized into two gestational periods (< 20 weeks and ≥ 20 weeks). Reference intervals were the 2.5th and 97.5th percentiles with 95% confidence intervals estimated by bootstrap resampling. Twin and singleton pregnancies were compared using the Wilcoxon rank-sum test.

A total of 734 women were included, contributing more than 1300 CBC samples and nearly 1000 biochemical samples. The mean maternal age was 32.5 years and the mean gestational age at delivery was 36.3 weeks. Compared with < 20 weeks, RBC, Hb, and Ht levels were lower at ≥ 20 weeks, whereas TG and TC levels were higher. Most other parameters showed modest changes. Compared with singleton pregnancies, Hb levels were lower after 20 weeks, and lipid levels were higher in twin pregnancies.

Twin pregnancies demonstrate distinctive hematologic and metabolic patterns across gestation. These reference intervals may improve laboratory interpretation and clinical management.