Effect of Reduced INR in Early Pregnancy on the Occurrence of Preeclampsia: A Retrospective Cohort Study

Abstract

To investigate the effect of reduced early-pregnancy activated partial thrombin time (APTT), prothrombin time (PT), and international standardized ratio (INR) on the risk of preeclampsia. A total of 8549 pregnant women with singleton births were included. Early pregnancy APTT, PT, and INR levels, with age, birth, prepregnancy body mass index, fibrinogen (FBG), thrombin time (TT), D-dimer (DD2), antithrombin III (ATIII), fibrin degradation products (FDP) as confounders, generalized linear model of APTT, the relative risk of PT and INR when INR reduction. After adequate adjustment for confounders, the relative risk of preeclampsia was 0.703 for every 1 s increase in plasma PT results in early pregnancy, and for every 0.1 increase in plasma INR results, the relative risk of preeclampsia was 0.767. With a PT less than the P25 quantile (<11 s), the relative risk of preeclampsia was 1.328. The relative risk of preeclampsia at an INR less than the P25 quantile (<0.92) was 1.24. There was no statistical association between APTT on the risk of preeclampsia. The relative risk of preeclampsia is strongly associated with a decrease in PT and INR in early pregnancy. PT and INR in early pregnancy were a potential marker in the risk stratification of preeclampsia. Focusing on reduced PT and INR levels in early pregnancy can help to identify early pregnancies at risk for preeclampsia.

Introduction

Preeclampsia (PE) is defined as hypertension associated with proteinuria (HTN) ¹ and occurs in 2% to 7% of pregnancies. ² According to the World Health Organization, it is one of the leading causes of maternal and neonatal morbidity and mortality worldwide (14%), especially in developing countries. ³ Although the exact etiology of preeclampsia is not fully understood, including changes in placental perfusion, endothelial dysfunction, fibrin deposition, inflammation, and hypercoagulability may be the etiology of the disease. In hypercoagulable states, approximately 15% of pregnant women die from preeclampsia due to an imbalance between coagulation and fibrinolytic activity, resulting in multiple thrombosis and rapid depletion of platelets, prothrombin, fibrinogen (FBG), and other coagulation factors.^4–6 Endothelial dysfunction is the main cause of various clinical symptoms in PE mothers, such as hepatic endothelial damage leading to hemolysis, elevated liver enzymes, and low platelet syndrome, vascular endothelial damage that can also lead to coagulation abnormalities, endothelial damage that exposes collagen fibers, triggers platelet aggregation and adhesion, and leads to placental ischemia and hypoxia, causing villi degeneration and necrosis, which releases coagulation substances and activates the exogenous coagulation system. It has been reported that the pathogenesis of PE is related to an imbalance of the coagulation-fibrinolytic system and that changes in coagulation appear early in the disease, usually before the appearance of clinical symptoms.^7,8 The abnormal enhancement of coagulation activity in the hypercoagulable state is associated with the pathogenesis of PE, suggesting an increased frequency of venous thromboembolic events, thromboplacental abnormalities, and thrombin generation in this population. ⁹

Under normal conditions, the body's coagulation and anticoagulation systems are in dynamic equilibrium, with mutual activation and restriction of the fibrinolytic and antifibrinolytic systems. This dynamic balance ensures both the flow state of blood in the vasculature and the integrity of the vascular wall to achieve hemostasis and coagulation in the body. Systemic small artery spasm in pregnant women with PE leads to systemic vascular endothelial injury, collagen fiber exposure, platelet adhesion, aggregation and antithrombin, massive platelet depletion, and blood in a prethrombotic state. The presence of extensive vascular endothelial injury in patients with hypertensive disorders of pregnancy can lead to the initiation of endogenous or exogenous coagulation mechanisms and a hypercoagulable state due to coagulation factor deficiency or mutations, which is particularly evident in patients with PE. This hypercoagulable state increases the risk of thrombosis. Numerous studies have shown ¹⁰ that the blood of pregnant women with PE is in a pathologically hypercoagulable state. More reports suggest that women with PE are prone to thrombosis and are in a prethrombotic state. However, some authors suggest that a prethrombotic state exists in patients with PE, which may selectively affect the uteroplacental circulation and lead to placental microthrombosis. PE-induced vascular endothelial damage can lead to platelet activation, adhesion, and aggregation in damaged areas and promote thrombin production, resulting in an altered coagulation status in vivo. Prothrombin time (PT) mainly reflects the level of coagulation factors such as I, II, and VII in the exogenous coagulation system in plasma and is a more sensitive screening test for the exogenous coagulation system. shortening of PT indicates hypercoagulation of blood and a tendency to thrombosis. One in three patients with eclampsia have a slightly prolonged PT. Routine coagulation tests are only altered in severe stages of PE, such as placental abruption.

Our study focused on PT and international standardized ratio (INR) in early pregnancy and aimed to observe the quantitative effect relationship between PT and INR levels and the risk of PE in early pregnancy by smoothing fitted curves and calculating the relative risk of PE when activated partial thrombin time (APTT), PT, and INL are reduced by generalized linear models.

Methods

Subjects

A total of 8549 pregnant singleton live births delivered at Fudan University Obstetrics and Gynecology Hospital between January 2021 and December 2021 were included in this study. Maternal clinical data and results were obtained from the clinical records. According to the current American College of Obstetricians and Gynecologists guidelines ¹¹ was diagnosed with preeclampsia at weeks 20 to 39 of gestation. The diagnostic criteria for preeclampsia are a new onset of hypertension (systolic 140 mm Hg or higher, diastolic 90 mm Hg or higher, or both) and proteinuria (2+ protein or larger strip urine test, 300 mg of protein, urine collection every 24 h) at 20 weeks of gestation. Serological examination at the first antenatal visit and recording of hypertension before 20 weeks of gestation were selected as confounders. Data on coagulation function have selected the test results of pregnant women during the first prenatal examination. The exclusion criteria of the study are as follows: taking drugs that affect coagulation function (such as antivitamin K treatment), confirmed hypertension, cardiovascular disease, severe anemia or immune disorder, untreated endocrine diseases, and lack of complete clinical medical records. This study is in line with the principles of the Declaration of Helsinki. It was approved by the research ethics committee of the Obstetrics and Gynecology Hospital Affiliated with Fudan University (2022-81).

Coagulation Function Test

At the first prenatal test, 2 ml of peripheral blood was collected into blood collecting vessels containing sodium citrate anticoagulant. The cells were centrifuged at 3000 r/min for 15 min. All peripheral blood samples were processed within 2 h of collection. PT, APTT, FBG, thrombin time (TT), D-dimer (DD2), antithrombin III (ATIII), and fibrin degradation products (FDP) were analyzed by an ACL TOP 700 fully automated hemagglutinate analyzer and supporting reagents. PT, APTT, FBG, and TT assays were determined by coagulation, DD2, and FDP by immunoturbidimetry assay, and ATIII by the hair color substrate assay. The INR was calculated by the (patient PT/normal control PT) ^ ISI. The coefficient of variation (CV%) was less than 10%.

Statistical Analysis

Data for continuous variables are presented as mean values (SD), and data for dichotomous variables are presented as percentages (%). Generalized linear models calculated the relative risk of preeclampsia with APTT, PT and INR reduction. Generalized linear models adjusted for confounding variables such as age, BMI, birth rate, FBG, TT, DD2, ATIII, FDP, and detecting gestational age. INR used 0.1 per change to report the relative risk of preeclampsia, in addition, PT, APTT, and INR also reported the relative risk of preeclampsia as a categorical variable, less than the P25th percentile as the positive exposure group, and the rest as the control group. Statistical analysis was performed using the SPSS software. All P values for statistics were 2-tailed, and a P < .05 was regarded as statistically significant.

Results

Table 1 describes the baseline characteristics of the subjects, including the demographic characteristics that may be related to the development of preeclampsia and the laboratory examination results of blood coagulation function.

Table 1.

Baseline Characteristics of the Study Participants.

	INR < P25 (<0.92)	INR ≥ P25 (≥0.92)	P Value
PE			.11
0	1673 (94.68%)	6482 (95.58%)
1	94 (5.32%)	300 (4.42%)
No. of participants	1767	6782
Test week （weeks）	12.18 ± 2.58	11.74 ± 2.55	<.001
Age (years), M (SD)	29.44 ± 2.78	29.16 ± 2.75	<.001
BMI (kg/m2), M (SD)	21.01 ± 2.85	21.07 ± 2.87	.43
PT (s)	10.74 ± 0.44	11.47 ± 0.56	<.001
APTT (s)	25.65 ± 1.83	26.76 ± 2.31	<.001
INR	0.89 ± 0.02	0.97 ± 0.04	<.001
FBG (g/L)	3.44 ± 0.57	3.44 ± 0.62	.958
TT (s)	17.06 ± 0.92	16.83 ± 1.00	<.001
DD2 (mg/L)	0.52 ± 0.45	0.46 ± 0.89	.004
ATIII (%)	92.41 ± 11.91	92.52 ± 14.75	.783
FDP (mg/L)	2.33 ± 1.84	1.92 ± 1.61	<.001
Parity			<.001
0	1371 (77.59%)	5513 (81.29%)
1	396 (22.41%)	1269 (18.71%)

Abbreviations: APTT, activated partial thrombin time; INR, international standardized ratio; FBG, fibrinogen; TT, thrombin time; DD2, D-dimer; ATIII, antithrombin III; FDP, fibrin degradation products; PT, prothrombin time; BMI, body mass index; PE, preeclampsia.

Table 2 shows the results of the generalized linear model analysis when PT, APTT, and INR are continuous variables. After adequate adjustment for confounding factors, the relative risk of preeclampsia was 0.703, (95% CI [0.508-0.982], P = .021) for every 1 s increase in plasma PT results in early pregnancy, and for every 0.1 increase in plasma INR results, the relative risk of preeclampsia was 0.767, (95% CI [0.593-0.91], P = .0965). However, there was no statistical association between early pregnancy APTT on the risk of preeclampsia.

Table 2.

Risk Ratio of Preeclampsia with PT、INR and APTT (Continuous Variable).

Exposure	Adjust Model
	RR	(95% CI)	P
PT	0.703	0.508-0.982	.021
APTT	1.022	0.954-1.080	.245
INR per 0.1	0.767	0.593-0.965	.012

Abbreviation: APTT, activated partial thrombin time; INR, international standardized ratio; PT, prothrombin time.

Adjust model: Adjusted for age, parity, body mass index, FBG, TT, DD2, ATIII, FDP, and test week.

Table 3 shows the results of the generalized linear model analysis when PT, APTT, and INR are categorical variables. After adequate adjustment for confounding factors, with PT less than the P25 quantile (<11 s), the relative risk of preeclampsia was 1.328, (95% CI [1.066-1.679], P = .002). When the INR was less than the P25 quantile (<0.92), the relative risk of preeclampsia was 1.24, (95% CI [0.968-1.536], P = .047). However, there was no statistical association between early pregnancy APTT on the risk of preeclampsia.

Table 3.

Risk Ratio of Preeclampsia with Continuous PT、INR and APTT (Categorical Variables).

Exposure	Adjust Model
	RR	(95% CI)	P
PT < 11 s	1.328	1.066-1.679	.002
APTT < 25 s	0.950	0.747-1.174	.319
INR < 0.92	1.240	0.968-1.536	.047

Abbreviation: APTT, activated partial thrombin time; INR, international standardized ratio; PT, prothrombin time.

Adjust model: Adjusted for age, parity, body mass index, FBG, TT, DD2, ATIII, FDP, and gestational age.

Discussion

There is no consensus on the relationship between APTT, PT, and INR and preeclampsia. Our study focused on APTT, PT, and INR levels around 12 weeks of gestation and evaluated their relationship with preeclampsia status. The results suggest that PT and INR at 12 weeks of gestation are risk factors for the development of preeclampsia. This is more valuable than examining the association of APTT, PT, and INR with preeclampsia after 20 weeks of gestation, when clinical signs of early eclampsia may occur. PT and INR in early pregnancy are important factors influencing the risk stratification management of preeclampsia. Close monitoring of pregnant women with reduced PT and INR in early pregnancy can help clinicians intervene early.

The pathogenesis of PE is unclear, but there is growing evidence that coagulation disorders and endothelial cell dysfunction are closely associated with the development of PE, with platelet activation occurring early in the pathogenesis of PE.^12–14 Endothelial cell dysfunction leads to abnormal platelet aggregation, adhesion, and coagulation. ¹³ Previous studies have confirmed ¹⁵ that platelet adhesion and aggregation rates are significantly higher in PE patients than in pregnant women of the same gestation period, due to the massive activation of platelet-activating factors, which leads to an aggregation and release response of platelets, further releasing platelet-activating factors in the circulation, inhibiting prostacyclin synthesis and further promoting vasoconstriction. In patients with PE, one of the coagulation and fibrinolytic systems is more severely affected by a maternal inflammatory response and immune dysregulation. ¹⁶ At the same time, placental ischemia, hypoxia, and enhanced cellular immune response due to inadequate placental blood supply, the release of large amounts of inflammatory cytokines by the organism, and damage to endothelial cells lead to vasospasm and constriction, resulting in increased blood pressure. ¹⁷ The PT reflects the activity of the exogenous coagulation system, ie detects the presence of defects or inhibitors of fibrinogen, coagulation factors, and prothrombin, and is used to detect congenital or acquired blood disorders. The APTT is used to detect the activity of the endogenous coagulation system, mainly detecting the concentration of coagulation factors IX, XI, and XII, and is commonly used in clinical practice to monitor the dosage of heparin. The TT value reflects the time taken to convert from fibrinogen to fibrin. During platelet agglutination, FIB acts on fibrinogen receptors on platelets, causing platelets to form clots through fibrinogen attachment. An increase in fibrinogen concentration can also reflect an intravascular inflammatory response. When coagulation activity is abnormally elevated in women during pregnancy, it will initiate fibrinolytic activity secondary to coagulation, resulting in a significant increase in DD levels. In recent years, “prothrombotic state” has been widely recognized as a high-risk factor in a number of studies related to adverse pregnancy outcomes. Patients with PE subsequently develop clinical symptoms and PE may develop as a result of delayed diagnosis and treatment of eclampsia. ¹⁸ Clinically, monitoring changes in coagulation allows for early diagnosis of PE, timely treatment, and improved patient prognosis.

Pregnant women with gestational hypertension have extensive vascular endothelial damage that can lead to the initiation of endogenous or exogenous coagulation mechanisms, and a hypercoagulable state is particularly evident in patients with PE. This hypercoagulable state increases the risk of thrombosis. Patients with PE have a prothrombotic state that may selectively affect the uteroplacental circulation, leading to placental microthrombosis and not necessarily to thrombotic disease. As an indicator of changes in the exogenous coagulation system, PT causes changes in synthetic and secreted coagulation and anticoagulation factors in patients with preeclampsia, as well as abnormal coagulation and fibrinolytic dysfunction due to vascular endothelial cell dysfunction and dysfunction. The physiological processes of endogenous coagulation of coagulation factor II, coagulation factor V, coagulation factor VII, coagulation factor III, coagulation factor IX, coagulation factor X, and platelet factor 3 (PF3), differentially higher than coagulation factors in pregnancy, as well as in patients with severe PE with increased fibrinogen content, further confirm that pregnant women with hypertension in pregnancy combined with blood are more prone to thrombosis and have the possibility of eclampsia. ¹⁹ EKUN et al ²⁰ showed that APTT and PT levels were significantly higher than in healthy pregnant women. OLADOSU-OLAYIWOLA et al ²¹ showed that there was no significant difference in APTT and PT levels between the PE and control groups and that malnutrition resulted in insufficient coagulation factors in the liver, which contributed to this balance. The results of previous studies are not fully consistent with the current study. FIB is a glycoprotein that becomes insoluble fibrin after hydrolysis by thrombin. It has the effect of enhancing intercellular bridging and reducing negative cell surface charge. Its level is related to thrombin activity and can be converted to fibrin in the coagulation pathway, which is an important indicator of hypercoagulable state in pregnant women. ²²

Several studies have found that the degree of elevated FIB is positively correlated with the severity of PE disease and that plasma FIB concentrations are significantly higher in PE patients than in healthy pregnant women. ²³ DD and FDP are products of fibrin monomer or fibrin (fibrinogen) after fibrinolytic degradation and can be used as indirect markers of thrombus formation and degradation, reflecting the dynamic process of coagulation to fibrinolysis. The concentrations of DD and FDP in pregnant women with PE increase from the beginning of pregnancy to delivery. ²⁴ The results of this study showed that the levels of APTT, PT, TT, and INR in the PE group with INR < P25 were significantly lower than those in the group with INR P25, which indicates endo- and exoclotting in PE with INR < P25, blood in a hypercoagulable state, as well as depletion of a large number of coagulation factors and further activation of the secondary coagulation system, showing shortening of APTT, PT, and TT; maternal between the two PE groups. There was no difference in FIB levels, suggesting that there would be a compensatory significant increase in FIB due to the hypercoagulable state of the blood system at the early stage of PE onset, and therefore there was no statistical difference in FIB between the two groups. DD and FDP concentrations were significantly higher in the PE group when INR < P25 than in the INR group when ≥ P25, a result that further suggests that activation of the coagulation pathway leads to a large release of prothrombin, which results in hyperfunction of the coagulation system secondary to the production of fibrinogen activator in the fibrinolytic system, ultimately leading to an increase in DD and FDP concentrations.

Prevention of PE is based on the detection of risk factors. There are many risk factors including genetic risk factors, family history of PE, immunological factors, zero births, new partners and demographic factors such as maternal age at 35 years, gestational age and birth weight of the woman (women born before at least 34 weeks or weighing less than 2500 g are at higher risk), pregnancy-related factors such as multiple pregnancies, congenital or chromosomal abnormalities, gravidity or urinary tract infections, the risk associated with risk of maternal disease-related factors, including chronic hypertension, kidney diseases, obesity, insulin resistance, diabetes, thrombosis, and environmental factors, such as living at high altitude and stress. Although it is important to identify these risk factors, they may not be effective in predicting PE. However, accurate prediction of PE has become a pressing issue in clinical practice. Several predictive tests are being evaluated, including clinical tests such as blood pressure measurement at mid-pregnancy or 24-h ambulatory blood pressure monitoring, but these tests lack sensitivity and specificity. ²⁵ In this study, we found that we analyzed the independent effects of PT and INR on PE by means of a generalized linear model with continuous variables. Then, the relative risk of preeclampsia was 0.703 (95% CI [0.508-0.982], P = .021) for each 1-s increase in plasma PT results in early pregnancy and 0.767 (95% CI [0.593-0.91], P = .0965) for each 0.1 increase in plasma INR results. In addition, we performed a generalized linear model analysis for categorical variables, and the relative risk of PT in preeclampsia was less than the P25 quantile (<11 s) at 1.328 (95% CI [1.066-1.679], P = .002). When the INR was less than the P25 quantile (<0.92), the relative risk of preeclampsia was 1.24 (95% CI [0.968-1.536], P = .047). However, there was no statistically significant association between APTT and the risk of early pregnancy PE. Therefore, PT and INR can be used as independent risk factors for PE by detecting PT and INR to prevent missing the optimal intervention window for delayed treatment.

Secondary prevention of PE is based on antiplatelet aspirin therapy, which reduces the risk of developing PE by 10% in women with at least one risk factor. ²⁶ No studies were allowed to determine the exact dose or optimal time to start aspirin. However, aspirin should be started as early as possible, before the initial 12 to 14 weeks, which corresponds to the start of the first phase of trophoblastic invasion. Therefore, whether it is possible to provide a strong reference for determining the optimal time to take aspirin by PT and INR testing still needs further study.

Conclusion

PT and INR in early pregnancy are strongly associated with the risk of preeclampsia. When PT and INR decrease in early pregnancy, the relative risk of preeclampsia increases. Clinicians should pay high attention to PT and INR levels in early pregnancy and enhance pregnancy monitoring, which is clinically important to reduce preeclampsia and avoid adverse pregnancy outcomes.