Rationale: Pregnancy has major effects on physiology in women. There have been many studies that established reference intervals but none was done in Vietnam. The recommendation by CLSI C28-A3 is that if possible, each laboratory establishes its own reference intervals.

Objective: To establish the reference intervals of complete blood count parameters and Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen.

Study design: This is a cross-sectional study.

Study population: Pregnant women with no history of disease and normal clinical findings.

Reference intervals (RI) is defined as the central 95% interval of the distribution of values taken from a biological reference population. RI is established for each trimester. The sample needed for each trimester is at least 258 which adds up to 774 when combining three trimesters.

Pregnant women are selected if eligible from obstetrics clinics after history taking and clinical findings. After consent, their blood are then drawn by phlebotomist into an ethylenediamine tetraacetic acid (EDTA) and a trisodium citrate 3.2% blood tube. EDTA samples are run on DxH 900 hematology analyzer, manufactured by Beckman Coulter and citrate samples are run on ACL TOP 550 coagulation analyzer, manufactured by Werfen. The analyzers are verified by laboratory procedure, recommended by Clinical and Laboratory Standards Institute (CLSI) method and quality control is checked before in accordance to the laboratory procedure.

Statistical analysis: Patients were divided into three groups, which are first, second, and third trimester. CLSI EP28-A3c recommended Dixon's D/R ratio outlier test to exclude outliers, where D is the absolute difference between the largest (or smallest) and the second largest (or smallest) observation, and R is the range of all observations. If D is equal to or greater than one-third of R, that observation is considered an outlier and is deleted. After outliers were deleted, the remaining data was tested again for additional outliers until there were no more outliers. A non-parametric method, recommended to establish reference intervals by CLSI EP28-A3c, was used to determine the lower reference limit 2.5th percentile and upper reference limit 97.5th percentile for each group.

Each reference limit was reported along with its 90th confidence interval. Groups were then compared using normal approximation with continuous correction Mann-Whitney U. A two-tailed P-value < 0.05 was considered significant. Statistical analysis was performed using NCSS statistical software (Utah, USA) version 2023

Inclusion Criteria:

• Singleton Pregnancy

Exclusion Criteria:

• Hypertension, Diabetes, Preeclampsia, Gestational Diabetes, Hemoglobinopathy, Current Infection, Positive Screening for Treponema pallidum, Hepatitis B Virus, HIV, usage of anticoagulant drug.

pregnant women at obstetrics clinics at Hung Vuong Hospital

data collected will be available when study is completed

starting 6 months after publication

Adverse events, including all-cause mortality, were not monitored or assessed during the study period. The study was limited to a one-time blood sample collection from each participant between June and August 2023, with no follow-up for adverse events.

All-Cause Mortality, Serious, and Other (Not Including Serious) Adverse Events were not monitored or assessed in this study. The purpose of the study was to evaluate laboratory reference intervals, and no clinical follow-up was performed.