To explore and compare the reference ranges of four coagulation tests in normal pregnant women during early and late pregnancy and the influence of age.

Values of four coagulation tests from 4 974 pregnant women, who gave single birth at Peking University First Hospital, Obstetrics and Gynecology Hospital of Fudan University, West China Second University Hospital, Peking University Third Hospital and Shengjing Hospital of China Medical University from February 2017 to July 2020, were measured and analyzed in this study, including prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen (Fib) and thrombin time (TT). The four normal reference ranges of coagulation during early and late pregnancy phases were expressed as P_2.5-P_97.5. The difference of two pregnancy phases was compared by non-parametric test of two related samples. And the difference between pregnant women of advanced and non-advanced age in the same pregnancy phase was compared by independent sample non-parametric test. Chi-square test was used to compare the incidence of pregnancy complications in different coagulation reference ranges.

The reference ranges of PT of normal pregnant women′s early and late pregnancy were 10.0-13.9 s and 9.6-12.3 s, the reference ranges of APTT were 22.6-35.3 s and 22.4-30.9 s, the reference ranges of Fib were 2.4-5.0 g/L and 3.0-5.7 g/L, the reference ranges of TT were 12.0-19.0 s and 11.5-18.4 s. Compared with early pregnancy, PT, APTT and TT shortened significantly, while the Fib significantly increased in late pregnancy (all P<0.001). PT, APTT and TT of advanced and non-advanced age pregnant women were significantly different (all P<0.01). Compared with the ranges of non-pregnant population, more pregnant women were included in the normal pregnant reference ranges of PT in early pregnancy and APTT in the early and late pregnancy, while the incidence of pregnancy complications had no significant differences (all P>0.05). The incidence of fetal distress was higher and the incidence of preterm birth was lower in the reference range of PT in late pregnancy. The incidence of gestational diabetes mellitus was higher in the early and late gestational Fib reference ranges, and the incidence of hypertensive disorders in pregnancy was higher in the late gestational Fib reference range (all P<0.05).

The coagulation function of pregnant women increases significantly with the growth of pregnancy, and there is a significant difference between advanced significantly and non-advanced age pregnant women. The recommended ranges of normal pregnant women′s early and late pregnancy PT are 10.0-13.9 s and 9.6-12.3 s, the recommended ranges of APTT are 22.6-35.3 s and 22.4-30.9 s, the recommended ranges of TT are 12.0-19.0 s and 11.5-18.4 s. The appropriate ranges of normal pregnant women′s early and late pregnancy Fib still need further exploration.

Prothrombin time; Partial thromboplastin time; Fibrinogen; Thrombin time; Pregnancy; Pregnancy complications; Age Factors