Pregnancy-specific reference intervals for complete blood count parameters in a Japanese cohort

To establish gestational age-specific reference intervals for complete blood count (CBC) parameters in a Japanese population and examine the influence of maternal body mass index (BMI) and age.

A retrospective cohort study was conducted at a single institution, analyzing eight CBC parameters in 33 355 singleton pregnancies. Reference intervals (2.5th-97.5th percentiles) for 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) were determined across early (<20 weeks), mid (20-29 weeks), and late (≥30 weeks) pregnancy. One-way analysis of variance with Tukey's intervals assessed the impact of BMI and age.

Up to 69 758 values per parameter were analyzed. WBC, MCV, and MCH increased in mid-pregnancy and then declined, while RBC and Ht reached their lowest levels in mid-pregnancy before partial recovery. Hb, MCHC, and PLT steadily decreased. Higher BMI was associated with higher WBC, RBC, Hb, Ht, and PLT at all gestational periods (p < 0.001). WBC declined, whereas MCV and MCH increased with maternal age, with more marked differences in late pregnancy. Hb decline was more evident in teenagers and women in their early 20s. Longitudinal comparisons showed lower WBC and higher PLT in the latest pregnancy compared to the preceding one (p < 0.001).

This study provides pregnancy-specific CBC reference intervals and highlights the need to consider BMI- and age-related factors in prenatal hematological assessment.