Predictive value of maternal serum placental growth factor, maternal clinical features, and fetal ultrasound indicators in preeclampsia

Abstract

Objective

This study was aimed to evaluate the predictive value of placental growth factor (PLGF), maternal risk factors, and maternal-fetal ultrasound indicators for preeclampsia(PE) and to analyze delivery outcomes associated with PE.

Methods

Pregnant women with PE(n = 80) and healthy controls(n = 160) were enrolled from the People’s Hospital of Guangxi Zhuang Autonomous Region between 2021 and 2022. Serum PLGF level were measured at various stages of pregnancy: early pregnancy, mid-pregnancy, and late pregnancy. Maternal clinical features, fetal ultrasound indicators, and pregnancy outcomes were also recorded.

Results

The serum concentration of PLGF was lower in the PE group compared to the control group throughout early, middle, and late pregnancy. At 20–24 weeks, the uterine artery resistance index was higher in the preeclampsia group (P < 0.05). Logistic regression analysis identified PLGF concentrations in early pregnancy and mid-pregnancy, along with mean arterial pressure (MAP), as independent factors for the onset of PE (P < 0.05).

Conclusion

PLGF could be used for prediction of PE in early pregnancy. A predictive model for PE was established by combining the PLGF concentrations in early and middle pregnancy with MAP.

Introduction

Preeclampsia(PE) has been recognized as the second leading cause of perinatal and maternal death, following postpartum hemorrhage. The incidence of PE is rising, now affecting 5–10% of pregnancies worldwide, largely due to increasing risk factors such as obesity, in vitro fertilization, and advanced maternal age [1]. PE is considered to develop in two stages. The first stage involves abnormal trophoblast invasion of uterine vessels during placental implantation, while the second stage is characterized by excessive maternal vascular inflammation and endothelial dysfunction, clinically presenting as new-onset hypertension, proteinuria, or other end-organ dysfunctions [2]. Anti-angiogenic factors(such as soluble Fms-like tyrosine kinase-1 receptor [sFlt-1] and soluble endoglin), as well as pro-angiogenic factors, (including vascular endothelial growth factor and placental growth factor [PLGF]), play crucial roles in the pathogenesis of PE. In patients with PE, the release of sFlt-1 is increased while free PLGF levels decrease, disrupting the balance of angiogenic factors contributing to the development of the condition. Altered levels of these factors can be detected weeks before clinical complications arise, enabling early diagnosis and prediction of maternal and fetal outcomes through peripheral blood testing. Currently, the sFlt-1/PLGF ratio and uterine artery index are used for early prediction of PE [3–4]. The Fetal Medicine Foundation (FMF) recommends combining PLGF, mean arterial pressure (MAP), and the uterine artery pulsation index (UT-PI) to predict PE in high-risk women between 11 weeks and 13 weeks + 6 days of gestation. Based on these indicators, detection rates for early-onset PE and preterm PE are estimated to be 90% and 75%, respectively, with a false positive rate of 10% [5]. This prediction method is considered superior to traditional assessments of maternal risk factors. For pregnant women with risk factors for PE, both the National Institutes of Health (NIH) guidelines together with the American College of Obstetricians and Gynecologists (ACOG) recommend administering aspirin before 16 weeks of pregnancy to improve placental perfusion and reduce the risk of preterm PE [6]. Due to the lack of specific clinical characteristics for PE, it is crucial for clinicians to closely monitor and diagnose the condition early when clinical risk factors emerge. This study aims to evaluate the predictive performance of PLGF in combination with maternal clinical features and fetal ultrasound indicators for PE and to analyze the associated pregnancy outcomes.

Materials and methods

Study population

Pregnant women receiving obstetric care at the People’s Hospital of Guangxi Zhuang Autonomous Region between 2021 and 2022 were included in this study. The estimation of the sample size for our study was based on the number of observed indicators, the chosen significance level(0.05), and practical limitations encountered in the actual work. The inclusion criteria included: (1) Women of childbearing age (≥ 20 years); (2) Pregnant women who received antenatal examinations during the early pregnancy (11 weeks to 13 weeks + 6 days), mid-pregnancy (14 weeks to 27 weeks + 6 days), and late pregnancy (after 28 weeks until delivery), and who delivered at the obstetric department of this hospital. The exclusion criteria were as follows: (1) Patients with serious internal or surgical diseases, such as pulmonary hypertension, congenital heart disease with heart function greater than grade III, chronic hypertension, or sepsis; (2) Patients who delivered at other hospitals after registering at our hospital or those who were lost to follow-up during pregnancy; (3)Patients with malignant tumors during pregnancy. Pregnant women with COVID-19 or gestational diabetes were not included in the exclusion criteria. A total of 329 participants were initially enrolled, and 89 subjects were excluded due to their decision to deliver at external institutions. Consequently, the final study sample included 160 participants in the normal control group and 80 participants with preeclampsia. All participants provided informed consent, and the study was approved by the Ethics Committee of People’s Hospital of Guangxi Zhuang Autonomous Region(registration number KY-SY-2021-17).

Observation indexes

The serum levels of PLGF were measured within the early, middle, and late stages of pregnancy. Maternal clinical parameters assessed included age, body mass index (BMI), mean arterial pressure (MAP), delivery time, delivery interval, as well as the presence of pregnancy complications. Pregnancy outcomes were evaluated in both PE and control groups, focusing on the mode of delivery, gestational age at delivery, total postpartum blood loss, neonatal birth weight, neonatal unit admission, and the occurrence of fetal growth restriction (FGR). Assessment using fetal ultrasound included: (1) Indicators of four-dimensional (4D) ultrasound: including the fetal umbilical artery pulsatility index (UA-PI), umbilical artery resistance index (UA-RI), and umbilical artery systolic/diastolic (UA-S/D) ratio; uterine artery resistance index (UT-RI); middle cerebral artery pulsatility index (MCA-PI) and middle cerebral artery resistance index (MCA-RI); (2) Fetal growth and development, including radial line measurements in middle and late pregnancy. Ultrasonography was performed by physicians with the title of attending physician or above. Doppler examinations were conducted with patients in a supine or semi-supine position, using a GE-E8 four-dimensional color Doppler ultrasound machine.

Research program

Pregnant women underwent risk assessment for PE during their initial prenatal visits. High-risk individuals for PE were identified based on medical history and clinical characteristics. PLGF testing was conducted at three time points: 11 to 13 weeks + 6 days, 14 to 27 weeks + 6 days, as well as after 28 weeks until delivery. The aforementioned maternal clinical parameters were prospectively collected. PE is characterized by a systolic blood pressure ≥ 140 mm Hg and/or diastolic blood pressure ≥ 90 mm Hg occurring after 20 weeks of pregnancy in women with previously normal blood pressure prior to conception. The diagnosis requires blood pressure measurements taken at least twice with a 4-hour interval and the presence of proteinuria.The diagnosis of PE was made at the time of admission for delivery. Participants were subsequently divided into the PE and control groups, and pregnancy outcomes were retrospectively analyzed after delivery.

Serum PLGF test

A 5 ml sample of fasting venous blood was taken from each participant. After centrifugation, the serum supernatant was stored at -80 °C until analysis. PLGF levels were quantified using the iRaTe 1600 dry fluorescence immunoassay system, following the manufacturer’s instructions.(Immunofluorescence reagent kit batch number: L01320201210, L01320200730).

Statistical analysis

Data analysis was performed using SPSS version 26.0. Continuous variables were presented as mean ± standard deviation (SD). We assessed normality using histograms and evaluated the homogeneity of variances using Levene’s Test. For normally distributed data, independent Student’s t-test was used for group comparison; while for non-normally distributed data, rank-sum tests were used for group comparison. Categorical data were expressed as frequencies and percentages and analyzed using Chi-square tests. Binary logistic regression analysis was adopted to evaluate the effect of clinical features, PLGF levels, as well as ultrasound parameters on PE outcomes. A P-value of less than 0.05 was considered statistically significant.

Results

Clinical characteristics

A total of 80 pregnant women with PE and 160 healthy controls were included. No significant differences were observed in parity, the interval between previous pregnancies, or age between the PE group and the normal control groups (P > 0.05). In contrast, the baseline BMI as well as MAP were much higher in the PE group when compared with the control group (P < 0.05). (Table 1)

Table 1 Comparison of clinical characteristics

Comparison of serum PLGF concentration

The PE group has a lower serum PLGF concentration throughout the early, middle, and late pregnancy stages in contrast to the control group (P < 0.05). (Table 2; Fig. 1)

Table 2 The serum concentration of placental growth factor(PLGF) PLGF1:PLGF concentration of early pregnancy, PLGF2:PLGF concentration of middle preganacy, PLGF3:PLGF concentration of late preganacy

Fig. 1

Serum concentration of placental growth factor(PLGF)

Comparison of delivery outcomes

The PE group experienced significantly earlier pregnancy terminations, greater postpartum blood loss, lower neonatal birth weights, higher rates of obstetric complications, and a significantly higher cesarean section rate compared to the control group (P < 0.05). (Table 3)

Table 3 Comparison of delivery outcomes

Comparison of the incidence of pregnancy complications

The PE group had significantly higher rates of embryo transfer, prior history of PE, ureaplasma urealyticum (UU) infection, placental abruption, obesity, uterine fibroids, and twin pregnancies in contrast with the control group (P < 0.05). No significant differences were observed in other complications such as gestational diabetes, Intrahepatic cholestasis of pregnancy(ICP), macrosomia, complete placenta previa, fetal distress between groups.(Table 4).

Table 4 Incidence of pregnancy complications

Comparison of fetal ultrasonic indicators

During the 4D fetal ultrasound examination conducted between 20 and 24 weeks, the UT-RI was significantly higher in the PE group in contrast with the control group (P < 0.05). Besides, no significant differences were observed in the UA-PI, UA-RI, UA-S/D, or fetal MCA-PI and MCA-RI. While differences in fetal humeral length (HL) and femoral length (FL) were statistically significant, they were not clinically meaningful. In the fetal ultrasound in late pregnancy, the menstrual lines were significantly smaller in the PE group in contrast with the control group (P < 0.05).(Table 5).

Table 5 Comparison of fetal ultrasonic indicators

Results of multivariate analysis

Results of binary logistic regression analysis showed that the PLGF concentration in early pregnancy(B=-0.013) and middle pregnancy stages(B=-0.005), and MAP(B = 0.187) was an independent factors influencing the occurrence of PE (P < 0.05). (Tables 6 and 7). The receiver operating characteristic (ROC) curve is shown in Fig. 2.

Table 6 Results of multivariate analysis

Table 7 ROC curve analysis results of PE predicted by multiple indexes

Fig. 2

The receiver operating characteristic (ROC) curve

Discussion

The aim of this study was to identify an economical and convenient method for early prediction of preeclampsia. We found that in pregnant women diagnosed with preeclampsia, PLGF decreased in the first trimester and this trend persisted throughout the pregnancy. The novelty of this study lies in the detection of PLGF starting from the 11th week of gestation, which contributes to the early prediction of PE. In underdeveloped regions, some women do not have regular prenatal check-ups due to economic pressure. Therefore, it is of great significance to seek a simple and cost-effective screening method. In normal pregnancies, the sFlt-1/PLGF ratio is stable, maximum differences between PE and normal pregnancies occur during the early phase, particularly between 24 and 28 weeks [7]. Previous studies have investigated the sFlt-1/PLGF ratio for the prediction of PE, but these studies were not prospective, did not incorporate ultrasound indicators, or had different inclusion and exclusion criteria [8,9,10]. The sFlt-1/PLGF ratio may be preferred over PLGF level alone for predicting PE, as well as maternal adverse outcomes. In twin pregnancies, the sFlt-1/PLGF ratio has also been proven to have predictive value for PE [11–12]. We did not conduct sFlt-1 testing but instead used fetal ultrasound indicators as combined prediction markers. This decision was based on clinical practicality: PLGF is currently being tested in clinical practice, while sFlt-1 testing has not yet been implemented. Moreover, four-dimensional ultrasound is an essential examination during pregnancy.

Prediction of PE involves evaluating clinical risk factors, MAP, and uterine artery ultrasonography [13–14]. BMI calculated as weight (kg) divided by the square of height (m²), is a significant risk factor for PE. A study found that overweight or obese women in China had a 3- to 5-fold increased risk of mild PE, and a 2- to 4-fold increased risk of severe PE compared to women with normal BMI. Additionally, multiple pregnancies were associated with at least a 4-fold increased risk of severe PE. While a history of diabetes and gestational diabetes mellitus was not associated with mild PE, it was linked to severe PE (odds rate [OR] 1.68, 95% confidence interval [CI] 1.19–2.35) [15].In the present study, pregnant women with PE had significantly higher MAP and baseline BMI compared to the control group. These results are consistent with other studies, while no statistically significant differences were observed in age, delivery time, or menstrual pregnancy interval.

An imbalance between angiogenic factors, particularly an increase in circulating anti-angiogenic factors such as sFlt-1 and a decrease in pro-angiogenic factors such as PLGF, plays a key role within the occurrence of PE. The sFlt-1/PLGF ratio has been used to predict FGR and preterm birth, although a ratio > 38 only has a positive predictive value of 36% [16]. The ISSHP 2021 guidelines recommended using angiogenic imbalance such as an elevated maternal sFlt-1/PLGF ratio or decreased maternal PLGF levels as a diagnostic criterion for PE [17]. Currently, PLGF has been tested clinically to assess placental function. In this study, serum levels of PLGF in the first and second trimesters were used to predict PE in women with high risk factors. The results showed that PLGF levels in pregnant women diagnosed with PE were lower than those in normal pregnant women throughout pregnancy, with statistically significant differences. This study suggests that PLGF may be useful for the early prediction of PE.

The ACOG, the NICE, and the ISSHP all recommend early screening for PE based on maternal risk factors [18]. Major risk factors for PE included a history of placental functional disorders (such as PE, FGR, and placental abruption), chronic hypertension, diabetes in pregnancy, obesity (pre-pregnancy BMI > 30), multiple pregnancies, antiphospholipid antibody syndrome, and other conditions such as systemic lupus erythematosus, a history of stillbirth, BMI > 25 during pregnancy, childlessness, assisted reproduction, advanced maternal age, and genetic predisposition. Less common factors included a family history of PE and trisomy 13 syndrome [19]. In this study, the incidence of complications during pregnancy was analyzed, revealing higher rates of assisted reproduction, a history of PE, UU infection, obesity, and twin pregnancies in the PE group compared to the control group. These findings were consistent with most risk factors for PE reported in the literature. Notably, the PE group included two cases of absent umbilical cord blood flow. One case resulted in an emergency cesarean section at 34 weeks of gestation, delivering a newborn weighing 1,260 g with a good prognosis. The other case ended in intrauterine fetal demise at 28 weeks and 5 days of gestation.

Pregnant women with early severe PE often have reduced blood flow in the umbilical artery together with increased resistance to blood flow. In normal pregnancies, the UA-PI, UA-RI, and UA-S/D ratio are correlated with the gestational age. An increased UA-PI can decrease placental blood supply, increasing the risk of FGR, fetal distress, and PE. The absence of umbilical artery blood flow or the presence of reversed end-diastolic flow may indicate that the fetus is near death. Studies have found that MCA-PI as well as MCA-RI are significantly lower in gestational hypertension and PE/eclampsia groups compared to normal pregnancies, although the MCA-S/D ratios does not show significant differences. MCA-PI or MCA-RI (measured between 35 and 40 weeks of gestation) and CPR have been identified as predictors of small for gestational age [20]. In the present study, the UT-RI among the women with PE was higher in contrast with the control group. An increased UT-RI on 4D ultrasound should raise suspicion for PE and prompt early intervention. Differences in fetal HL and FL observed on 4D ultrasound were statistically significant but did not have clinical relevance.

The limitations of this study were as follows: (1) Due to sample size limitations, only 6 factors (PLGF1, PLGF2, PLGF3, MAP, BMI, UT-RI) could be included in the multivariate analysis based on a P value < 0.05. (2) The study only included UT-RI results without measurements of uterine artery pulsatility index (UT-PI). (3)The diagnosis of PE was assessed after admission, making it difficult to precisely determine the initial gestational week of PE onset. Performing PLGF testing early in gestation for pregnant women with high-risk factors may provide outpatient physicians with important information for timely intervention, potentially preventing or delaying the occurrence and progression of PE. This study conducted preliminary analysis of clinical data, PLGF and ultrasound indicators, the effect on PE still needs to be confirmed in larger sample size studies.

Conclusion

In conclusion, this study demonstrated that serum levels of PLGF decreased throughout pregnancy in patients with PE, especially during early pregnancy. Therefore, PLGF could be used for the early prediction of PE; predictive model for PE was established by combining the PLGF concentration in early and middle pregnancy with MAP.