Introduction

The placenta, a round organ, reflects prenatal events and weighs about 470 grams with a diameter of 22 centimeters and a thickness of 2.5 centimeters. It’ is essential for fetal growth, providing nutrition, oxygen, and waste removal. During pregnancy, it facilitates maternal-fetal communication, hormone synthesis, and immunological tolerance1. Preeclampsia is a serious condition typically arising after 20 weeks of gestation, identified by sudden high blood pressure, often with protein in the urine. If a woman experiences two instances of elevated blood pressure within four hours, she should seek immediate medical attention2.

Preeclampsia is characterized by placental dysfunction, resulting in diminished blood flow and uteroplacental insufficiency, which in turn impacts fetal development and poses potential complications3. The compromised placenta induces endothelial dysfunction and distinct symptoms. The condition advances through two stages due to abnormal placentation and insufficient cytotrophoblast invasion, disrupting normal fetal development. Consequently, placental growth retardation and functional derangement impair fetal growth, leading to significant health consequences in newborns and later in life4.

Previous research has demonstrated that histological changes, such as fibrinoid necrosis, syncytial knots, calcifications, and endothelial proliferation, are notably elevated in the hypertensive cohort5. These alterations signify vascular damage within the placenta, which may compromise its ability to adequately facilitate fetal oxygenation and nourishment. Furthermore, the presence of these histological aberrations may serve as prognostic indicators for potential maternal and neonatal health complications6. These findings underscore the critical importance of vigilant blood pressure monitoring throughout gestation and the timely and effective management of preeclampsia to mitigate the possibility of adverse outcomes for both the mother and the neonate7.

The experience of motherhood is a profound one, and it is imperative to address the health challenges that many women encounter during this transformative period. Previous research into placental changes and their correlation with preeclampsia has predominantly centered on participants from Western nations. However, it is essential to acknowledge the multifaceted nature of these conditions, taking into consideration genetic, immunological, environmental, social, and cultural factors. Consequently, further research is indispensable to yield conclusive evidence.

The present study aims to contrast placental histomorphometry in preeclampsia and normal cases, to acquire a comprehensive understanding of the underlying pathological mechanisms. The primary goal of this project is to build a foundational body of knowledge in our nation, educate medical professionals about the effects of preeclampsia on placental macro and microarchitecture, and advocate for early identification and treatment to improve delivery outcomes. This research has the potential to furnish invaluable insights into the determinants of preeclampsia and related disorders, ultimately contributing to the development of more efficacious treatment and management options.

Materials and methods

Study settings, design and population

An institutional based comparative cross sectional study design was conducted at Arba Minch General Hospital, located in Arba Minch town, Gamo zone, Southern Ethiopia. Before Arba Minch University Comprehensive and Teaching Specialized Hospital was established, Arba Minch General Hospital served as the only referral hospital in Gamo Zone, Southern Ethiopia.

The hospital gives services in internal medicine, obstetrics/gynecology, surgery, and pediatrics, and serving 113,000 patients a year. Its clinical staff consists of 114 BSc nurses, 45 general practitioners, 52 midwives, 16 specialists, 6 integrated emergency surgical officers, 45 general practitioners, 30 health officers,1 ophthalmologist, 4 optometrists, 3 ophthalmic nurses,, 12 anesthetists, 3 HMIS, 28 laboratory technicians, 28 laboratory technologists, 34 pharmacists, 8 radiologists and 3 psychiatry nurses.

Eligibility criteria

Inclusion criteria

Pregnant women who were diagnosed to have preeclampsia and those pregnant women without preeclampsia were included.

Exclusion criteria

Maternal conditions that results in intrauterine growth restriction, change in the histology and gross morphology of the placenta, such as anemia, malaria, preexisting diabetes mellitus, multiple pregnancy, diagnosed single umbilical artery, and multiple pregnancy were excluded.

Sample size determination and sampling procedure

The sample size was calculated using Epi info version 7.2.5.0, based on the following assumptions; power = 80%, ratio of exposed to non-exposed = 1:3, percentage of outcome in unexposed = 53.4%, percentage of outcome in exposed = 83.3%.

The total sample size calculated was 119 which includes 30 (number of cases) and 89(number of controls)8.

As Arba Minch General Hospital has a pathology laboratory for pathological examination, it was purposively selected. Cases were chosen sequentially in order of arrival, and three consecutive controls were selected for each case using simple random sampling technique.

Study variables

Dependent variables

Pathological changes of placenta9, Gross morphology of the placenta, and Birth outcomes.

Independent variables

Socio-demographic variables, Obstetric data of the mothers, Gravidity and mode of delivery.

Operational definitions

Pathological changes of placenta

The Histo-pathological changes are characterized by one or more of the following features; syncytial Knots, Cytotrophoblastic proliferation, Cellular proliferation, Fibrinoid, Necrosis, Endothelial Proliferation Calcification, and Fibrosis.

Cases

Full-term pregnant women diagnosed with preeclampsia.

Controls

Full-term pregnant women without preeclampsia, experiencing uncomplicated pregnancies.

Preeclampsia diagnosis criteria

Preeclampsia is diagnosed as new-onset hypertension (systolic BP ≥ 140 mmHg and/or diastolic BP ≥ 90 mmHg) occurring after 20 weeks gestation with or without proteinuria in accordance with clinical guidelines10.

Complete term pregnancy

Examined as deliveries occurring between 37 + 0 and 40 + 6 weeks of gestation. This strict reference was set in order to ensure homogeneity in the analysis of placental morphology11.

Birth outcomes

Primary outcome was measured as weight (grams) of the neonate immediately post birth which provides a quantifiable measure of fetal growth.

Data collection tools and procedures

The data were collected using a structured interviewer administered questionnaire combined with observational checklist. The questionnaire was prepared or adopted using different literatures3,12,13. It was divided into sub-sections covering to Socio-demographic characteristics and obstetric history. The observational checklist contains birth outcome related items and assessment of placenta including gross and microscopic findings.

The midwife collected placentas immediately following delivery in a sterile tray. The placentas were then subjected to thorough washing under running tap water and subsequently weighed using a traditional weighing machine. Following weighing, the placentas were immersed in a 10% formalin solution, then carefully placed in a formalin-filled jar and labeled with corresponding codes. The specimens were subsequently transported to the pathology department of Arba Minch General Hospital for gross and microscopic examination by the primary investigator and the pathologist. Detailed assessments, including measurements of the diameter and thickness of each placental tissue piece, evaluation of cord insertion, fetal membrane condition, cord vasculature, and placental cotyledons, as well as determination of the presence of retroplacental hemorrhage, extensive infarction, and fibrosis, were conducted. Additionally, calcification, fibrosis, necrosis, and hemorrhage were assessed on the cut surface of the placenta.

A representative sample of placental tissue, encompassing placental samples from the fetal and maternal surfaces, one cord sample, and a rolled fetal membrane sample, was collected and securely packaged in a single cassette labeled with a specific code. Cassettes containing placental tissue from cases and controls were stored in separate marked containers to prevent formalin leakage. Subsequently, these tissue cassettes were transported to the Pathology Laboratory of Alatyon General Hospital, Hawassa, Ethiopia for tissue processing and staining. The tissue underwent processing using a semi-automated tissue processor to remove formalin, followed by embedding in paraffin wax employing a tissue embedding system. The embedded tissue blocks were then sectioned at a thickness of 3–5 μm using a microtome, after which they were prepared for staining.

Hematoxylin and Eosin staining was performed using an automated tissue stainer, and the stained and labeled tissue slides were assessed by a pathologist at the Histology Laboratory of Arba Minch University. The primary investigator conducted an examination of the slides alongside the pathologist using a multi-headed microscope and documented histopathological findings in structured checklists based on the corresponding codes. Each tissue slide was methodically evaluated for the presence of syncytial knots, cytotrophoblastic cellular proliferation, fibroid necrosis, endothelial proliferation, calcification, hyalinized villi, and fibrosis. Comprehensive gross and microscopic findings were recorded for both each cases and controls according to the specific codes.

Data processing and analysis

After ensuring the completeness and consistency of the data, they were entered into Excel and exported to SPSS version 21 for analysis. Descriptive statistics, such as frequency, mean, and standard deviation, were calculated and presented using tables and graphs to characterize the study variable. The chi-square test was employed to assess placental histology in preeclampsia mothers compared to normotensive mothers. Fisher’s exact test was used for histological changes with expected cell counts of less than 5. Furthermore, an independent t-test was utilized to compare the mean placental measurement and mean birth weight between different groups. Additionally, a point biserial correlation analysis, a special type of Pearson correlation, was conducted to evaluate the relationship between birth weight and histopathologic changes. Statistical significance was attributed to results with a p-value of less than 0.05.

Data quality assurance

Data cleaning assessed completeness, consistency, outliers, and missing values. Data collectors and supervisors received two days of training on the study purpose, datacollection tools, techniques, and ethical procedures. A pretest was conducted on 5% of the sample outside the study area, and necessary revisions were made. To ensure consistency, 5% of the collected data were randomly selected and crosschecked; any discrepancies were corrected by supervisors and investigators. During the datacollection period, the principal investigator reviewed 5% of the forms daily for completeness.

Results

Socio-demographic characteristics

Among 119 mothers who participated in this study, 30 were preeclampsia and 89 were normotensive. More than half of controls, 46 (51.7%), were in the 26–32 age group, while three-fifths of the cases were in the 18–25 age group. Regarding the educational status,5(16.7%) of cases and 3(3.4%) of controls were illiterate (Table 1).

Table 1 Socio-demographic characteristics of study participants.
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Obstetric and birth outcome characteristics

Among the participants 63.3% of cases and 44.9% of controls were primigravidae. In the case group 63.3% delivered via spontaneous vaginal delivery, compared to 61.8% in the comparative group. Cesarean section was utilized by 38.2% and 36.7% of participants in the comparison and case groups, respectively (Fig. 1).

Fig. 1
figure 1

Obstetric data distribution of the study participants.

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In this study, among the babies delivered from the case and comparison groups, 5.6% of the babies in the comparative groups and 53.3% of the babies delivered from preeclampsia mothers were underweight. For the case and comparative groups, the mean birth weight was 2.5 kg ± 0.59 and 3.3 kg ± 0.51, (P = 0.001), respectively. It was observed that NICU admissions to hospitals in the case group was higher than controls, 11 (36.7%), 5 (5.6%), respectively (Table 2).

Table 2 Birth outcome of deliveries of study participants among cases and controls.
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Using point Biserial correlation the correlation between birth weight and histopathological changes was determined and found that it was significantly correlated(correlation coefficient = 0.343,P < 0.001).

Histomorphometric findings of the placenta among cases and controls

The morphometric changes of the placenta were observed. The mean diameter of the placenta among cases was lower than controls 14.16 ± 1.29, 17.97 ± 1.84, respectively (P < 0.001).Similarly the weight of the placenta among cases was significantly lower than controls, measuring 463.33 ± 64.23grm and 649.4 ± 135.36grm, respectively, P = 0.001).

Among cases, 10% of the participants exhibited gross calcification compared to 2% in the control group. Retroplacental clotting was observed in 25.8% of the controls and 90% of the cases. Concerning cord insertion morphology, central cord insertion was detected in 23.3% of the cases and 49 (l.4%) of the controls. The eccentric type of cord insertion was found in 36.7% of the cases and 44.95% of the controls, while marginal cord insertions were observed in 90% of the cases and 5.6% of the controls.

On the other hand histopatholgical changes of the placenta were also recorded (Fig. 2). Cytotrophoblastic cellular proliferation was lower in controls than cases, rating 12.4% and 50%, respectively, P = 0.001. Fibrosis necrosis was observed higher in case group than control (40% vs. 11.2%, P = 0.001). Hyalinized villi and microscopical calcification seen in 16 (18%) of the comparative groups and 18 (60.0%) of the case groups(P = 0.001) (Table 3).

Fig. 2
figure 2

Different features of the Histo-phatalogical changes of Placenta.

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Table 3 Histomorphometry changes of placenta among cases and controls.
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Discussion

The objective of this study was to conduct a comparative analysis of placental histomorphometry between mothers affected by preeclampsia and those with normotensive pregnancies. The research entailed an examination of the gross morphological and histological characteristics of placentas procured from preeclamptic and normotensive pregnant women admitted to Arba Minch General Hospital. The findings revealed distinct differences, with placentas from the preeclamptic cohort displaying reduced average diameter, thinner walls, and diminished overall size in comparison to placentas from normotensive counterparts.

The outcome is consistent with research conducted in Addis Ababa, Ethiopia, which discovered a significant distinction between the case and comparison groups in terms of average birth weight and placental features. In particular, the case group showed lower average birth weight and thinner placenta compared to the comparison group, as demonstrated by the statistical analyses. Likewise, results from a study in Ghana indicated a marked difference in mean placental weight between the case and comparison groups, which aligns with our findings14,15.

It is further supported by a study conducted in Nepal, there was a significant difference in mean placental weight and size between the control and case groups. The case group had a smaller mean placental diameter and thickness compared to the control group7.

The placenta’s lower weight, thickness, and size in women with preeclampsia may be due to poor blood flow, which results in insufficient nutrition and oxygen supply to the placenta, compromising its growth, capacity to grow and expand appropriately, and function. As a result, placental tissue may be thinner, smaller, and lighter than in a typical pregnancy.

In this study, the comparison group had a lower rate of syncytial knot formation, cytotrophoblastic cellular proliferation, and fibrinoid necrosis in terms of placental histological alterations compared to the case group. The findings are consistent with a study conducted in Pakistan, which discovered that syncytial knots were present in 62% of case groups and 22% of comparison groups, as well as fibrinoid necrosis and cytotrophoblastic cellular development in 66% and 68% of cases, respectively. The comparison groups’ results showed that 14% of instances exhibited cytotrophoblastic cellular growth, 18% had fibrinoid necrosis, and 22% had syncytial knots. An additional study conducted in Iraq found that the case group had higher histological alterations than the comparator group16,17.

Additionally, compared to mothers with normal blood pressure, preeclamptic women had a greater prevalence of histological abnormalities in numerous Indian investigations. The results of two studies, one conducted at Muhimbli National Hospital and the other showing a similar result support our findings that histological alterations are more common in preeclamptic mothers than in normotensive mothers12,18.

The study found that 53.3% of babies born to preeclamptic mothers and 5.6% of children in comparison groups were underweight. The case group had a mean birth weight of 2.5 kg ± 0.59, while the comparison group had a mean of 3.07 kg ± 0.55. This aligns with a Ghanaian study indicating significantly lower birth weights in the case group15.

Strength and limitation of the study

As strength it offers a unique placental tissue histomorphometric analysis and provides a better evaluation of preeclampsia-related alterations than a gross examination and improves comprehension of the pathophysiology of disease by using microscopic analysis.

The limitation of the study may include: causal inferences are not possible with a cross-sectional design and incapable of evaluating long-term impacts or temporal relationships.

Conclusion

The study found that preeclamptic women had more placental histopathology changes than normotensive women, with lighter and smaller placentas. Birth weight positively correlates with these alterations. Therefore, mothers with preeclampsia need appropriate obstetric care to minimize risks. This research will give insight to conduct future research on similar topic with large sample size.

Ethical considerations

The Institutional Review Board (IRB) of Arba Minch University granted ethical approval with protocol number IRB/23,092/2023. To obtain consent for data gathering, a formal letter of cooperation and ethical approval was given to the obstetrics and pathology department of Arba Minch General Hospital. Written informed consent was obtained from all participants. To protect patient privacy, the patient’s medical chart was coded during data collection. Every checklist has a code as well. The acquired result was disclosed anonymously, and no personal connection was made to the patient’s medical history. This study was conducted in accordance with the Declaration of Helsinki.