Research
HJOG 2026, 25 (1), 55-64 | doi: 10.33574/hjog.0615
Hamideh Pakniat1,2, Mohammad Ali Hosseini3, Shokouh Sadat Aboutorabi1,2, Azam Rasti2, Mohadeseh Nabiei2, Fatemeh Sadeghi Niaraki4
1 Department of Obstetrics and Gynecology, School of Medicine, Kowsar Hospital, Qazvin University of Medical Sciences, Qazvin, Iran
2 Non-Communicable Diseases Research Center, Research Institute for Prevention of Non-Communicable Diseases, Qazvin University of Medical Sciences, Qazvin, Iran
3 Men’s Health and Reproductive Health Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
4 Mazandaran University of Medical Sciences, Sari, Iran
Correspondence: Mohammad Ali Hosseini, M.D , Department of Obstetrics and Gynecology, Qazvin University of Medical Sciences, Qazvin, Iran, E-mail: smahoseini@gmail.com
Abstract
Objective: Subchorionic hematoma (SCH) is considered as one of the most frequent complications during pregnancy. The Purpose of the present study was to explore the potential relationship between SCH during the first trimester of pregnancy and maternal and neonatal outcomes in singleton pregnancies.
Methods: This case-control study was performed from January 2024 to January 2025.In the present study, 552 pregnant women included based on the inclusion criteria (276 with SCH and 276 without SCH). Of these, 276 were diagnosed with SCH based on first-trimester ultrasound findings (case group), and the remaining 276 had no signs of SCH (control group).
Results: A significant relationship was observed between SCH and certain adverse outcomes, including preterm delivery, NICU admission, and miscarriage rates (P<0.05). Nevertheless, no significant differences were identified between the SCH and control groups regarding other complications such as preeclampsia, Apgar scores at 1 and 5 minutes, placenta accreta, premature rupture of membranes (PROM), intrauterine growth restriction (IUGR), or low birth weight (LBW) (P>0.05). Moreover, 34 women (13.5%) had hematomas measuring greater than 3 cm in size, while 215 women (85.7%) had hematomas of 3 cm or smaller (P<0.05)
Conclusion: These findings highlight the significance of close monitoring and intensive care for pregnant women diagnosed with SCH to mitigate potential risks and adverse outcomes.
Keywords: Subchorionic hematoma, singleton pregnancies, pregnancy outcomes, first trimester.
Introduction
Subchorionic hematoma (SCH) refers to the accumulation of blood between the chorionic membrane and the uterine wall in the subchorionic space, resulting from the separation of the chorion from the endometrium(1). SCH can lead to pregnancy loss, which is its most important complication. Additionally, the pooling of blood between the chorionic membrane and the uterine wall could leak through the cervical canal, causing vaginal bleeding, which may cause pelvic pain(2). Other adverse outcomes associated with SCH include preterm delivery, placental abruption, intrauterine fetal death, small-for-gestational-age (SGA), low Apgar scores, and preeclampsia(3). However, some studies have reported no association between intrauterine hematoma and these perinatal complications(4, 5). For instance, Yin et al. found that first trimester subchorionic hematoma, specifically between 6 and 8 weeks of gestation, was not associated with adverse pregnancy outcomes in singleton pregnancies(6). These discrepancies in findings may be related to differences in sample size, study design, and heterogeneity among the studied populations.
Subchorionic hematoma (also referred to as subchorionic hemorrhage) can be a significant source of anxiety for women with singleton pregnancies(7). Additionally, SCH is recognized as one of the most common abnormalities during pregnancy, with its prevalence ranging from 0.46% to 39.5% across various studies since its first description in 1981(8-10). Most of these hematomas (approximately 60%) occur in the first trimester. In most cases, small or moderate hematomas decrease in size over time(4, 11). However, large hematomas, which separate at least 30-40% of the placenta from the endometrium, might enlarge and exert increased pressure on the gestational sac, potentially leading to spontaneous miscarriage(12). If the hematoma continues into the late first trimester or early second trimester, the risk of partial placental abruption from its attachment site increases, which may be associated with a poorer prognosis compared to early first-trimester hematomas(13).
Although the exact cause of SCH is not still completely understood, several factors have been proposed as potential contributors, including uterine abnormalities, a history of recurrent miscarriages, infections, and autoimmune conditions such as coagulation disorders, positive antiphospholipid antibodies, reduced activity of protein S and antithrombin III levels, elevated homocysteine levels, and the presence anticardiolipin, lupus anticoagulant, and antinuclear antibodies have been identified as risk factors for SCH(4, 5, 14). Additionally, it has been hypothesized that the primary trigger of this condition is poor placentation, which may disrupt angiogenesis and lead to the formation of weak blood vessels that are prone to rupture(6, 15). Factors associated with an increased risk of adverse pregnancy outcomes in SCH include early diagnosis (before 9 weeks), advanced maternal age, large-sized hematoma, fundal or retroplacental location, and the severity of symptoms(16, 17).
Given that the prognosis for pregnant women with visible hematomas is lower compared to those without such findings, imaging plays a critical role in evaluation(18). Furthermore, with the increased use of early pregnancy ultrasound monitoring, the prevalence of asymptomatic subchorionic hematomas has risen significantly. On ultrasound examination, SCH, primarily caused by the rupture of marginal placental uterine veins, appears as a crescent-shaped hypoechoic or anechoic area between the chorionic membrane and the myometrium, with its lower edge often associated with the internal cervical os(12). Changes in the size or status of the hematoma can be assessed through regular ultrasound follow-ups. To ensure diagnostic accuracy, these sonographic findings must be correlated with clinical symptoms such as vaginal bleeding and pelvic pain, underscoring the importance of physical examination in patient assessment(4, 19).
The clinical significance of SCH is still controversial, with controversial results reported in studies examining maternal and fetal outcomes following SCH. Despite existing studies, the association between SCH and adverse pregnancy outcomes remains unclear due to limited data. Given the limitations of previous studies, the aim of this study was to investigate the relationship between first-trimester SCHin singleton pregnancies and maternal and fetal outcomes.
Material and methods
This case-control study was conducted at Qazvin University of Medical Sciences, Qazvin, Iran. After obtaining written informed consent from participants and receiving approval from the ethics committee (Institutional Review Board (IRB) approval: IR.QUMS.REC.1403.205), sampling started. The study was carried out from January 2024 to January 2025 and included 552 pregnant women (276 with SCH and 276 without SCH) diagnosed during first-trimester ultrasound examinations. All ultrasound assessments were performed by a single specialist. Participants in the study were matched based on baseline characteristics, including age, gestational age, parity, and body mass index (BMI).
Sample Selection
The sample size was calculated based on a study by Irina (20), accounting for a 10% dropout rate. Inclusion criteria consisted of mothers with singleton pregnancies and a gestational age between 6 and 14 weeks who were referred to the ultrasound center. Intrauterine pregnancy with a confirmed gestational age was verified by a radiologist. Gestational age was determined based on the first day of the last regular menstrual period. For women with irregular menstrual cycles, gestational age was confirmed by first-trimester ultrasound.
Exclusion Criteria
Individuals with the following conditions were excluded from the study: multiple pregnancies, congenital fetal anomalies, use of assisted reproductive technologies, placenta previa, chronic diabetes, genital tract infections, polycystic ovary syndrome, uterine abnormalities, hysterectomy, placental adhesion, COVID-19 infection, intrahepatic cholestasis, a history of postpartum hemorrhage, coagulation disorders, hypo- or hyperthyroidism, renal diseases, immune system disorders, hematologic disorders, pre-pregnancy anemia, nutritional deficiencies, or chronic hypertension.
Data Collection
Demographic information, including age, height, weight, gestational age at study entry, and hematoma size as reported in the ultrasound, was recorded using a researcher-designed questionnaire. The first ultrasound report of each patient, performed between weeks 6 and 10 of pregnancy, was reviewed to determine the presence or absence of SCH and its size. Since most subchorionic hematomas are crescent- or oval-shaped, their size was calculated by multiplying the three measured dimensions on the ultrasound and dividing the result by two. Patients with SCH were evaluated based on the initial hematoma size measured between weeks 6 and 10 of pregnancy. These patients were followed up with ultrasounds every 7 to 14 days until the hematoma resolved completely. In contrast, patients without SCH underwent their first ultrasound during the same period and were evaluated two to three more times during the first trimester for diagnostic purposes and to assess fetal nuchal translucency thickness. Sampling continued until the required number of cases and controls was achieved.
Follow-up
Patients were monitored in accordance with the Iranian Ministry of Health’s National Pregnancy Care Protocol until delivery, with follow-up evaluations conducted either in-person or by telephone every 7-14 days. All pregnancy complications, including miscarriage, preterm delivery, preeclampsia, premature rupture of membranes (PROM), intrauterine growth restriction (IUGR), and placental adhesion, were systematically recorded. Postpartum data collection included documentation of gestational age at delivery, neonatal birth weight, Apgar scores, and NICU admissions. A comprehensive review of hospital medical records was performed to verify maternal medical history and pregnancy-related complications.
The study evaluated the following complications using standardized diagnostic criteria: Miscarriage was defined as pregnancy loss prior to 20 weeks’ gestation with fetal weight <500 g; preterm birth as delivery before 37 completed weeks; PROM as membrane rupture prior to labor onset (categorized as TPROM before 37 weeks and PPROM after 37 weeks); IUGR as estimated fetal weight below the 10th percentile on ultrasonography; and low birth weight (LBW) as neonatal weight <2500 g. Preeclampsia was diagnosed by blood pressure ≥140/90 mmHg with proteinuria emerging after 20 weeks’ gestation.
Thyroid dysfunction classifications included: overt hypothyroidism (TSH >10 mIU/L or decreased FT4), subclinical hypothyroidism (TSH 2.5-10 mIU/L with normal FT4), and isolated hypothyroxinemia. Intrahepatic cholestasis of pregnancy required elevated serum bile acids. Gestational diabetes mellitus (GDM) was diagnosed per glucose tolerance testing thresholds (fasting ≥5.1 mmol/L, 1-hour ≥10.0 mmol/L, or 2-hour ≥8.5 mmol/L). Oligohydramnios was defined as amniotic fluid volume ≤300 mL or amniotic fluid index ≤5 cm.
This standardized follow-up protocol ensured comprehensive documentation of maternal-fetal outcomes while maintaining consistency with international diagnostic criteria.
Statistical Analysis
Data were analyzed using SPSS software (V.26). Variables were presented as mean ± standard deviation (SD) or median (IQR), as appropriate. The Kolmogorov-Smirnov test was used to assess data normality. Qualitative variables were compared using the chi-square test, while quantitative variables were analyzed using t-test or the Mann-Whitney U test. The Pearson or Spearman correlation test was applied to examine associations between variables, as appropriate. P-value < 0.05 was considered statistically significant.
Results
As demonstrated in Figure 1, the study initially included 552 pregnant women, of whom 6 were excluded due to fetal anomalies, 12 due to stillbirth, and 33 due to twin pregnancies, resulting in a final analytical cohort of 551 participants. This cohort consisted of 251 women with SCH in the case group and 250 women without SCH in the control group. Analysis of pregnancy outcomes revealed 19 cases (7.6%) of spontaneous miscarriage in the SCH group compared to 7 cases (2.8%) in the control group, demonstrating a statistically significant difference (p=0.008).
Figure 1. Flowchart
Examination of baseline demographic characteristics presented in Table 1 showed no significant differences between groups in terms of maternal age, body mass index (BMI), gravidity, parity, or history of previous miscarriage (all p>0.05). However, a statistically significant difference was observed in gestational age at study enrollment, with the SCH group averaging 11.07 weeks compared to 11.48 weeks in controls (p<0.05), While this 0.41-week difference reached statistical significance, its clinical relevance may be questionable due to the minimal absolute difference observed.
Ultrasonographic evaluation of the 251 SCH cases demonstrated that 34 women (13.5%) had hematomas measuring greater than 3 cm in size, while 215 women (85.7%) had hematomas of 3 cm or smaller. Comparative analysis of pregnancy complications, as detailed in Table 2, revealed significantly higher rates of preterm delivery (15.1% vs. 8.0%, p=0.02) and neonatal intensive care unit (NICU) admission (18.3% vs. 10.4%, p=0.01) in the SCH group compared to controls.
No statistically significant differences were observed between groups for the following outcomes: preeclampsia (p=0.32), placenta accreta (p=0.45), premature rupture of membranes (PROM) (p=0.67), intrauterine growth restriction (IUGR) (p=0.21), or low birth weight (LBW) (p=0.15). Evaluation of immediate neonatal outcomes showed no significant differences in Apgar scores at either 1 minute (SCH: 8.92 ± 0.39 vs control: 8.92 ± 0.37, p>0.05) or 5 minutes (SCH: 9.92 ± 0.39 vs control: 9.93 ± 0.36, p>0.05) after delivery.
These findings collectively demonstrate that while the presence of SCH is associated with increased risks of spontaneous miscarriage, preterm delivery, and NICU admission, it does not appear to significantly affect other measured maternal or neonatal outcomes, including immediate postnatal wellbeing as assessed by Apgar scoring. The clinical implications of these results suggest that pregnancies complicated by SCH may require enhanced monitoring for specific adverse outcomes while potentially not necessitating additional intervention for other parameters that show no significant association with SCH.
Discussion
In the present study, among the 251 participating mothers with SCH, 34 cases (13.5%) had a hematoma size exceeding 3 cm, while 215 cases had a hematoma size below 3 cm. Given that ultrasound examinations were performed between 6 and 14 weeks of gestation (mean: 11.07 weeks), these findings align with those of other studies. McKenzie et al., showed that the maximum diameter of SCH was reported as 2.1 cm for gestational ages 6–13 weeks, 4.2 cm for 14–17 weeks, and 4.3 cm for 18–21 weeks(13).
A study by Lou et al. demonstrated that the size of SCH was not associated with pregnancy loss before 20 weeks, although vaginal bleeding was more pronounced in cases with larger hematomas. Additionally, they found that women who experienced miscarriage had earlier detection of SCH, a finding consistent with the results of our study(21). Our results are also in agreement with the study by Shayesta Rahi, which reported that hematoma size was less than 5 cm in 15% of cases and greater than 10 cm in 16.6% of cases, with smaller hematomas being more prevalent(15).
Moreover, no significant difference was observed between the two groups regarding the association between SCH and the development of preeclampsia. A 2021 study by Taşkömür et al., investigating the impact of SCH in women with threatened abortion (TA) and a control group similarly found no significant differences in preeclampsia or placental abruption between the groups, which is consistent with our results(18). However, they reported no significant difference in preterm labor between the study groups, contrary to our findings, and noted a significant difference in LBW, which was not observed in our study. In their study, 1-minute Apgar scores showed a significant difference between groups, while 5-minute Apgar scores did not, whereas in our study, neither 1-minute nor 5-minute Apgar scores demonstrated significant differences. Disruption of natural uterine mechanisms, including both contractile and relaxant mechanisms present in normal pregnancies, may lead to the release of uterine mediators and increase uterine contractions(22). This increased contractility could result in higher rates of preterm labor. It has also been reported that increased uterine contractility may reduce the risk of postpartum uterine atony(7). Other studies, such as the case-control study by Shafaq Hanif et al. comparing mothers with threatened abortion symptoms in groups with and without SCH, found a significant difference between the two groups regarding preeclampsia(17). Conversely, a study by Sumaira Naz et al. reported no association between preeclampsia and SCH(23). The varying results across different studies regarding the association between SCH and preeclampsia may be due to several factors. Differences in study designs, including variations in sample size, patient inclusion and exclusion criteria, and data collection methods; hematoma size and location (where larger hematomas or those in specific uterine locations may increase the risk of preeclampsia); and patient demographic characteristics such as age, medical history, socioeconomic status, and ethnicity, can all influence outcomes. These factors indicate the need for further studies with standardized and controlled designs to better elucidate the relationship between SCH and preeclampsia.
In our study, a significant association was observed between the presence of SCH and preterm delivery (P=0.02), with the preterm delivery rate being significantly higher in the SCH group compared to the non-SCH group. Our findings are consistent with studies by Ayser Hashem, Rahi, and Al Memar, which confirmed the association between SCH and increased risk of preterm delivery(12, 24, 25). In contrast, studies such as those by Shafaq Hanif and Chongjuan did not report this association(9, 17). A study conducted by Anna Palatnik et al. also aligned with our results, demonstrating a significant association between preterm delivery and SCH(26). Furthermore, they showed that SCHis associated with shortened cervical length, which could be one of the factors contributing to preterm delivery. The mechanisms underlying adverse pregnancy outcomes associated with SCH are not yet fully understood(27). One proposed theory suggests that chronic inflammation in the placental membranes and decidua may lead to premature rupture of membranes. In this context, ischemia, thrombosis, and necrosis in the decidua cause bleeding and thrombin formation, which can activate inflammatory responses(20). Overall, these changes may result in spontaneous miscarriage or preterm delivery during pregnancy. According to the results of the present study, the rate of NICU admission for infants born to mothers with SCH was higher than for those born to mothers without hematoma, showing a significant difference between the case and control groups (p=0.021). This finding is consistent with the results of Ayser Hashem’s study, while studies by Hevee Zendin Ali and Xu reported no significant association between SCH and increased NICU admission rates after birth(12, 28, 29).
The current study found no significant association between SCH and premature rupture of membranes (PROM) (P=0.15), a finding that is also confirmed by Chongjuan’s study(9). Regarding intrauterine growth restriction (IUGR), no significant association was observed between SCH and this outcome in our study (P=0.329), with similar results being reported in studies by Chongjuan and Alberto Borges Peixoto, while Ayser Hashem’s study demonstrated that SCH significantly affects IUGR development(9, 12, 27). For low birth weight (LBW), our study found no significant difference between case and control groups (P=1), with both groups reporting 17%, which aligns with the results of Alberto Borges Peixoto’s study, whereas Ayser Hashem’s study reported a significant association between SCH and LBW(12, 27). Numerous studies support the existence of a significant relationship between SCH and miscarriage. In the present study, a significant association was found between SCH and miscarriage occurrence (P=0.025), with 13 miscarriage cases in the control group and 7.1% in the case group. Multiple studies, including McKenzie, Shafaq Hanif, Ayser Hashem, Shayesta Rahi, Alberto Borges Peixoto, and Irina Bushirova, confirm this result and demonstrate a significant association between SCH and miscarriage(12, 13, 15, 17, 20, 27), with only Al Memar’s study not reporting this significant association(24). Regarding Apgar scores, the mean and standard deviation of the 1-minute Apgar score in the control group was 8.92±0.37 and in the case group 8.92±0.39, showing no significant difference between the two groups. Similarly, the mean and standard deviation of the 5-minute Apgar score in the control group was 9.93±0.36 and in the case group 9.92±0.39, with no significant difference observed. These findings are consistent with the results of studies by Chongjuan and Hevee Zendin Ali, although Shafaq Hanif’s study suggests that SCH may influence neonatal Apgar scores after birth(9, 17, 28).
Recommendations
Based on the findings of this study, it is recommended that mothers with SCH receive enhanced monitoring and specialized care to prevent known complications of this condition and avoid adverse pregnancy outcomes. This targeted approach should focus particularly on the early detection and management of preterm labor risks and potential miscarriage, while maintaining standard obstetric care for other pregnancy parameters that showed no significant association with SCH. The implementation of such specialized monitoring protocols could significantly improve maternal and neonatal outcomes in SCH-affected pregnancies.
Conflicts of interest
The authors declare that they have no competing interests.
Source of funding
The authors declare that there was no source of funding.
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