Preterm birth is a common cause of neonatal morbidity and mortality, accounting for about 12 percent of all newborns (1–3). A fully functioning placenta can provide newborns with essential materials, and loss of function can lead to pregnancy complications (4). Placental microscopy and histopathological features are of great significance in explaining the etiology of preterm birth and may also be one of the new methods of disease classification (5–7). The Amsterdam classification system defines four patterns of placental pathology for placental injuries, including maternal vascular malperfusion (MVM), acute intrauterine infection/inflammation (AI), fetal vascular malperfusion (FVM), and chronic inflammation (CI) of unknown etiology (8). F Arias et al. found that MVM and AI are two important placental pathological subtypes of preterm birth and preterm premature rupture of membranes (PPROM) (9).

Elisabeth B et al. found that AI was associated with necrotizing enterocolitis (NEC) in extremely preterm infants (< 28 weeks) (OR12.2 95%CI 1.1, 137.1), and MVM was associated with decreased fetal birth weight (10). Other studies have shown that MVM can lead to more severe bronchopulmonary dysplasia in newborns (11, 12), And might be associated with an increased risk of neurodevelopmental abnormalities in children at 2 years old (13). Co-occurrence of MVM and AI may be a specific form of placental lesions associated with RDS and IVH in preterm birth (14). However, many references exist about the relationship between placental lesions and adverse outcomes. There is still little information on the occurrence of single or combined placental lesions in pregnant women in the Asia population (15), which is not conducive for Chinese pathologists and obstetricians to obtain information and compare it to other countries (16). At the same time, evidence in different classifications has supported the relationship between placental lesions and preterm birth (17, 18). However, there is limited evidence about the relationship between single placental pathology or superimposed pathology with the outcome in preterm births with or without premature rupture of membranes (PROM), and thus, further exploration is needed (19).

Therefore, this study aims to retrospectively explore data from our hospital and discuss the relationship between the single or co-occurrence of MVM and AI with outcomes such as gestational age (GA), birth weight, neonatal respiratory distress syndrome (RDS), and intraventricular hemorrhage (IVH) in literature (14, 19, 20). Finally, through the above research, we hope to highlight the application value of standardized placental pathological interpretation in diagnosing and treating diseases.

Maternal and infant information was grouped according to preterm birth and rupture of membranes. Categorical variables were analyzed with chi-square tests. After Continuous variables were tested for normal distribution and homogeneity of variance, using ANOVA or Kruskal-Wallis test, as appropriate. P values were corrected for multiple testing using the Bonferroni procedure. Categorical variables are expressed as quantities and percentages. The continuous variables were expressed as mean ± standard deviation if normally distributed and as median (P25, P75) if not normally distributed. Linear regression was used to simulate the GA and birth weight Z-score (MVM-/ AI- as a reference, compare the cases of MVM-/ AI+, MVM+/ AI-, and MVM+/ AI+) and expressed as β, P. We conducted logistic regression analyses to determine the associations between placental findings and neonatal RDS and IVH. Results were expressed as Odds Ratio (OR) 95% confidence intervals (CI). The covariates selected a priori mainly included age, college education, and pre-pregnancy BMI. During the discussion of RDS and IVH, the GA covariate will be added as an adjustment. R (Version 4.2.2) software was used for the above statistical analysis, and P < 0.05 was considered statistically significant.

From 01. January. 2021 to 31. December. 2022, clinical information on 990 pregnant women and newborns was assessed. Pregnant women were divided into four groups based on preterm birth and premature rupture of membranes. There were 651 term pregnant women, including 538 with intact membranes and 113 with PROM. There were 339 preterm pregnant women, including 260 with intact membranes and 79 with PPROM (Figure 1).

Among the four groups, low education was more likely to occur in preterm pregnancy with intact membranes (84%, 85.8%, 60%, and 74.7%, respectively; P < 0.001). Preterm pregnancy with intact membranes was more likely to develop hypertension (chronic hypertension 3.5%, 0.9%, 7.3%, 1.2%, and gestational hypertension 7.1%, 1.7%, 13.5%, 2.5%, respectively; P < 0.001). Newborns in preterm pregnancy with intact membranes were more likely to have a 1-minute Apgar score < 7 (1.5%, 0.0%, 26.2%, 10.1%, respectively; P < 0.001), 5-minute Apgar score < 7 (1.1%, 0.0%, 20.0%, 7.6%, respectively; P < 0.001). Newborns in preterm pregnancy with intact membranes were more likely to have RDS (0.7%, 0.0%, 31.9%, 31.6%, respectively; P < 0.001) and BPD (0.0%, 0.0%, 8.1%, 6.3%, respectively; P < 0.001) and the IVH (0.9%, 0.9%, 20.0%, 17.7%, respectively; P < 0.001) adverse outcomes. Among the four groups, Placental lesions are more likely to occur in preterm infants with intact membranes, including decidual arteriopathy (2.6%, 3.5%, 9.6%, 5.1%, respectively; P = 0.010) and placental infarction (15.4%, 22.1%, 13.5%, 5.1%, respectively; P < 0.01). However, FIRS (1.5%, 1.8%, 2.7%, 6.3%, P = 0.049) and severe HCA (21.9%, 26.5%, 23.1%, 44.3%, respectively; P < 0.001) were higher in pregnant women with PPROM. Advanced Syncytial knots (65.1%, 61.1%, 58.8%, 65.8%, respectively; P = 0.34), Perivillous fibrin deposition (58.4%, 58.4%, 49.2%, 50.6%, respectively; P = 0.07) and Intervillous fibrin deposition (2.8%, 4.4%, 3.1%, 1.3%, respectively; P = 0.634) were not statistically significant among the four groups (Table 1).

After adjusting the covariates of age, college education, and pre-pregnancy BMI, the effects of MVM-/AI-, MVM-/AI+, MVM+/AI- and MVM+/AI+ on GA and Z-score of the newborns were explored.In reference to MVM-/AI-, MVM−/AI+ at term was paradoxically associated with, on average, slightly longer gestations (difference 0.6 weeks, p = 0.02). MVM-/AI+ and MVM+/AI+ were associated with shorter gestational weeks of newborns (Adjusted GA −4.7, and−3.0, both P < 0.001). MVM-/AI + and MVM+/AI+ with intact membrane (Adjusted GA −5.4, P < 0.001 and −3.8, P = 0.001) PPROM (Adjusted GA −4.3, P = 0.006 and −2.6, P = 0.038) may result in a shorter gestational age in preterm birth. In reference to MVM-/AI-, MVM+/AI+ was associated with lower birth weight for preterm birth (adjusted birth weight Z-score −2.6 and −1.8, both P < 0.001). In preterm infants, MVM-/AI+ and MVM+/AI+ with intact membrane (adjusted birth weight Z-score −3.0, and −2.4, both P < 0.001) versus PPROM (adjusted birth weight −2.4, P = 0.011 and −1.6, P = 0.041) were associated with lower birth weight (Table 2, Figures 2A, B).

In this study, a higher risk of RDS in newborns in MVM+/AI + was observed only in preterm populations with OR 2.2 (95%CI 1.03, 4.9); however, this association was not observed after further adjustment for gestational age at birth as a covariate (Table 3). No association with IVH and RDS was observed in comparisons of MVM-/AI+, MVM+/AI-, and MVM+/AI+, regardless of intact membranes or PPROM. However, after adjusting for pre-pregnancy BMI, Age, college education, and GA, we observed a significant increase in MVM-/AI+, MVM+/AI-, and MVM+/AI+ (Adjusted OR 0.9, 1.5, and 1.8) in RDS. Although there was no statistically significant difference in disease risk, the risk of disease occurrence showed an increasing trend. This trend was observed in preterm women with intact membranes (adjusted for OR 0.9, 1.8, 1.8) and in women with PPROM (adjusted for OR 0.2, 0.4, and 1.0).

Proper placental function is essential for exchanging and transporting nutrients and waste between mothers and newborns. This study investigated the relationship between MVM, AI alone, or with co-occurrence of adverse outcomes in pregnant women in China and further investigated the relationship between placental disease and preterm birth with or without PPROM.

The following key information was obtained through this retrospective study. First, although no effect of MVM was observed on either outcome, pathological features of MVM and AI were dominant in preterm birth with intact membranes and PPROM. It is suggested that MVM and AI are two important subtypes of placental lesions. This partly explains the differences between the different types of preterm birth. Second, the presence of MVM or AI alone and co-occurrence was associated with shorter GA and lower birth weight in newborns. The coexistence of MVM and AI may be a unique pathological form that needs attention, providing a unique perspective and thought for explaining the pathological mechanism of neonatal diseases. Finally, the presence of MVM or AI alone and co-occurrence in RDS reflects an increasing trend of disease risk, suggesting that different degrees of placental lesions may be closely related to the risk of disease occurrence. Predicting the severity of diseases from the perspective of placental lesions may be possible and may provide theoretical support for implementing disease intervention and reducing the risk of short—and long-term poor prognosis of diseases.

In this study, AI alone, MVM alone, MVM, and AI co-occurrence were associated with lower birth weight and shorter GA in preterm birth. Karen Mestan’s study confirmed that placental infection/inflammation is related to postpartum fetal growth and may be an effective indicator for predicting postpartum fetal growth failure (24). The inflammatory cascade induced by AI is an essential mechanism of preterm birth (25–27). Microorganisms are recognized by innate immune system monitoring receptors (TLRs), leading to the activation of pro-inflammatory transcription factor nuclear factor Kappa-B (NF-kB) and the production of downstream pro-inflammatory cytokines (27–29). Microbial endotoxins and pro-inflammatory cytokines stimulate the production of prostaglandins, other inflammatory mediators, and stroma-degrading enzymes. Prostaglandins stimulate uterine contraction, and degradation of the extracellular matrix of the fetal membrane can lead to PPROM (25). This may explain why the incidence of HCA and FIRS in this study’s PPROM population was higher than in other groups.

The diagnosis of MVM does not depend on any single placental finding but rather on a series of findings involving primary changes in the maternal decidual vasculature of the mother and/or secondary changes in the villous parenchymal (30). MVM is also a pathological phenomenon in preeclampsia, stillbirth, fetal growth restriction, and other diseases (31–33). Although MVM did not differ among the four groups, co-occurrence of MVM and AI was associated with shorter GA and weight loss in our study, suggesting that MVM remains a significant placental lesion. It has been reported that direct detection of placenta-related biomarkers—continuous cycle maternal placental growth factor can lead to a high proportion of patients with a poor perinatal prognosis, which helps test disease treatment strategies to improve clinical prognosis (34).

As a result, pathologists will likely encounter lesions of AI and MVM in daily practice and provide useful information about the underlying causes of preterm birth (4). In response to the emergence of AI, some guidelines recommend using antibiotics before pregnancy to reduce the risk of developing AI if suspected (35, 36). While there is no specific treatment for MVM, potential management options include optimizing maternal health and paying attention to cardiovascular status, glucose tolerance, and weight (37–40). Other possible interventions include susceptibility assessment, uterine artery doppler, early placental ultrasound in the third trimester, drug therapy, and early delivery in subsequent trimesters (41–43). At the same time, it has been suggested that pathologists should be aware of the emergence and evolution of MVM and associated pathological lesions and strive to use standardized diagnostic templates to identify placental lesions (30). Because accurate identification has potential clinical relevance/prognostic implications for mothers and children, consistent reporting may advance our deeper understanding of placental lesions to improve management and identify potential treatments (44).

This study’s limitations are as follows: first, the present study is a single-center retrospective study, and evidence from a large-sample multi-center prospective study is required to determine whether the findings apply to the women in China. Second, there is still a gap in the interpretation of placenta pathology in our hospital compared with other countries. Although we also supplemented the data by integrating indicators from other literature, standardized diagnostic templates are still needed to identify placental lesions in subsequent clinical diagnosis and treatment to enhance the general value of clinical reports and identify potential therapies.

The strengths of this study are as follows. First, data in this study is from the Chinese population, which is of particular reference value for comparing different races to those previously documented. Second, the present study provides evidence on the relationship between the appearance of placental pathology alone or co-occurrence and guides subsequent researchers to design and further explore the research direction. Thirdly, through this study, we also realized the non-standardization and application limitations of the existing placental pathology interpretation and made timely improvements. The subsequent standardized diagnosis of placenta pathology promotes the universality of placental pathological interpretation reports. In clinical application, it can guide the diagnosis and treatment of diseases more scientifically.

MVM and AI are two important subtype placental lesions associated with adverse outcomes in preterm infants. AI or MVM alone and a combination of both lesions may be associated with an increased risk of certain diseases. Therefore, it is of great significance to improve the standard of placental pathology interpretation to standardize its general application, guide disease diagnosis, and make the diagnosis and treatment plan scientifically.