Characteristics of patients with subchorionic hematomas in the second trimester
Dr Tetsuo Yamada, Department of Obstetrics and Gynecology, International University of Health and Welfare Hospital, 537-3 Iguchi, Nasushiobara, Tochigi 329-2763, Japan. Email: firstname.lastname@example.org
Aim: The aim of this study was to investigate the etiological characteristics of patients diagnosed with subchorionic hematoma.
Methods: A case-controlled study was performed to compare characteristics of patients and controls. Via ultrasound examination, 47 pregnant patients were found to have subchorionic hematomas and 1075 had no evidence of subchorionic hematomas (controls). In the second trimester, patients were compared with regard to endocervical Chlamydia trachomatis and other vaginal microorganisms.
Results: The overall incidence of subchorionic hematomas in this pregnant population was 4.2%. Maternal clinical characteristics did not differ between cases and controls. Evaluation of the vaginal flora revealed that the positive rates of coagulase-negative staphylococci (cases: 12.8%; controls: 4.1%; P < 0.01) and Gardnerella vaginalis (cases: 12.8%; controls: 2.5%; P < 0.001) in the cases were significantly higher than those of the controls. The negative rate of Lactobacillus in the cases was significantly higher than that of the controls (cases: 42.6%; controls: 27.6%; P < 0.05).
Conclusion: Pregnant women with subchorionic hematoma in the first trimester showed changes in vaginal flora in the second trimester, which suggests a possible association with subchorionic hematoma and vaginal flora change.
Subchorionic hematoma is defined as a sonographically-detected, intrauterine, echo-free area located between the membranes and the uterine wall. In 1981, Mantoni and Pederson first described its sonographic patterns as an anechoic area with a falciform shape.1 The previously reported incidence of subchorionic hematoma ranges from 0.5%2 to 22%.3 Possible reasons for the discrepancy in these rates include variable pregnant populations, a wide range of gestational ages and the lack of a standard definition for subchorionic hematoma. Recently, some studies have reported that the overall incidence of subchorionic hematomas in patients with an accurate definition ranges from 1.3%4 to 3.1%.5
Some reports have suggested that these lesions increase the risk of spontaneous abortion,3,6 fetal growth restriction5,7 and preterm delivery.3,5 Other reports suggest that a subchorionic hematoma does not increase adverse pregnancy outcomes.8–10
Subchorionic hematoma is believed to result from a blood collection secondary to the separation of the chorionic plate from the underlying decidua; however, the etiology and physiology of this type of hematoma are currently unclear, and an effective therapy has not been developed. The aim of this study was to investigate the etiological characteristics of patients diagnosed with subchorionic hematoma, particularly in relation to their obstetric history and vaginal flora in the second trimester.
Patients and Methods
Before initiation of this case-controlled study, approval was obtained from the International University of Health and Welfare Hospital Ethics Committee. During the period between January 2006 and September 2009, all patients who underwent prenatal care at the International University of Health and Welfare Hospital were recruited for participation. Gestational age was calculated on the basis of the last menstrual period and was corrected when the crown–rump length measurements were more than seven days different from that date. All patients who provided informed consent were offered a sonographic examination and underwent routine first and second trimester ultrasound examinations by transvaginal or transabdominal methods. Subchorionic hematoma was defined as a falciform-shaped, echo-free area between the chorionic membrane and the myometrium.1 All ultrasound examinations were performed by the perinatologists in our department using a Sonovista-C3000 machine (Mochida Siemens, Tokyo, Japan). Inclusion criteria were intrauterine, singleton gestation pregnancies with no uterine or fetal abnormalities. The following patients were excluded: those with a multiple gestation pregnancy, who desired pregnancy termination, who did not visit the institute after second trimester, who had received antibiotics before a vaginal flora culture was taken, and those with a spontaneous abortion in the first trimester. As suggested by a previous article,11 hematoma volumes were estimated by measuring the maximum transverse, anteroposterior, and longitudinal diameters and multiplying these values by the constant 0.52.
Patient demographic data (i.e. age and body mass index [BMI]), cigarette smoking status and pregnancy history, such as induced or spontaneous abortion, cesarean delivery and vaginal delivery) were obtained by questionnaire, interview and review of medical records.
In the second trimester, after informed consent was obtained, a clean, non-lubricated speculum was placed into the vagina. The lateral vaginal fornix was swabbed for detection of vaginal flora and the endocervical canal was swabbed for detection of Chlamydia trachomatis. The vaginal swabs were cultured for aerobic and genital mycoplasmas. Chlamydia trachomatis detection tests were provided by Clearview Chlamydia MF (Inverness Medical Japan, Tokyo, Japan).
Two-sample t-tests were analyzed to compare continuous variables and the χ2-test or Fisher's exact test were used to compare categorical variables. A two-tailed P value <0.05 was considered to be statistically significant. Odds ratios and 95% confidence intervals were computed. StatMate III (ATMS, Tokyo, Japan) was used for the statistical analysis.
Between January 2006 and September 2009, 1376 patients underwent routine first trimester obstetric ultrasonographic examination at our institution. Of these 1376 patients, 52 were excluded from this study due to the presence of multiple gestation (45) or therapeutic abortion because of fetal abnormalities or maternal complications (7). A total of 28 patients were lost to follow up after the second trimester and 10 patients had uterine abnormalities; these 38 patients were also excluded. Furthermore, 164 patients suffered a first trimester spontaneous abortion; therefore, a total of 1122 patients met the inclusion criteria for analysis. Of these, 47 developed subchorionic hematoma. At first detection of the subchorionic hematoma, the mean gestational age was 8.2 weeks. The average hematoma volume was 10.8 cm3 (minimum: 0.2 cm3; maximum: 105.3 cm3).
There were no significant differences between the hematoma and control groups with regard to maternal age, body mass index or cigarette smoking. Furthermore, there were no significant differences between the hematoma and control groups with regard to induced or spontaneous abortion, prior cesarean delivery or prior vaginal delivery (Table 1).
Table 1. Basic clinical characteristics of the study population
|Maternal age (years; mean ± SD)||31.2 ± 5.0||30.4 ± 4.9||0.236|
|Body mass index (kg/m2; mean ± SD)||21.0 ± 2.9||21.3 ± 3.34||0.618|
|Smoking||7 (14.9%)||176 (16.3%)||0.788|
|Gravity|| || || |
| ≥1||26||688|| |
|Parity|| || || |
| Parous||21||543|| |
|History of induced abortion|| || || |
| ≥1||2||132|| |
|History of spontaneous abortion|| || || |
| ≥1||13||191|| |
|History of cesarean delivery|| || || |
| ≥1||9||134|| |
|History of vaginal delivery|
| ≥1||17||421|| |
In the second trimester, 1122 patients met the criteria for vaginal flora analysis via culture technique in the second trimester. With regard to the positive rates of Chlamydia trachomatis in the endocervix, there were no significant differences between the hematoma and control groups. With regard to the positive culture rate of vaginal flora, there were no significant differences between the groups for Candida, Escherichia coli, Group B streptococci, α-Streptococcus, Corynebacterium, Staphylococcus aureus, Mycoplasma hominis or Ureaplasma urealyticum. The positive culture rate of coagulase-negative staphylococci in the hematoma group was significantly higher than that of the control group (P < 0.01; odds ratio [OR]: 3.4; 95% confidence interval [CI]: 1.4–8.5). The positive culture rate of Gardnerella vaginalis in the hematoma group was also significantly higher than that of the control group (P < 0.001; OR: 5.7; 95% CI: 2.2–14.5). The negative culture rate of Lactobacillus in the hematoma group was significantly higher than that of the control group (P < 0.05; OR: 2.0; 95% CI: 1.1–3.6) (Table 2).
Table 2. Prevalence of major vaginal microorganisms
|Lactobacillus||27 (57.4%)||782 (72.7%)||0.022|
|Ureaplasma urealyticum||17 (36.2%)||409 (38.0%)||0.795|
|Candida||8 (17.0%)||191 (17.8%)||0.895|
|Gardnerella vaginalis||6 (12.8%)||27 (2.5%)||0.0004|
|Staphylococcus, coagulase negative||6 (12.8%)||44 (4.1%)||0.004|
|Group B Streptococcus||3 (6.4%)||56 (5.2%)||0.724|
|Escherichia coli||3 (6.4%)||75 (7.0%)||0.875|
|α-Streptococcus||2 (4.3%)||13 (1.2%)||0.075|
|Staphylococcus aureus||2 (4.3%)||11 (1.0%)||0.183|
|Chlamydia trachomatis||2 (4.3%)||18 (1.7%)||0.191|
|Corynebacterium||1 (2.1%)||6 (0.6%)||0.695|
|Mycoplasma hominis||1 (2.1%)||9 (0.8%)||0.356|
The overall incidence of subchorionic hematomas in this series was 4.2%. This incidence is similar to those found by Ball4 and Nagy5 in all pregnant patients with an accurate definition. Therefore, the definition of subchorionic hematoma used in this study appears to be appropriate.
We investigated the etiology of subchorionic hematomas. In particular, we focused on the patients' basic characteristics and reproductive history that affected uterine status. We selected body mass index and smoking as the patients' basic characteristics, and found that these factors were not related to the development of subchorionic hematoma. We selected the reproductive history with regard to induced abortion, spontaneous abortion, cesarean delivery and vaginal delivery. Although these events physically affect the endometrium, they were not related to the development of subchorionic hematoma. Our findings suggest that a woman's basic clinical characteristics and prior physical uterine events (such as curettage or delivery) do not affect the development of subchorionic hematoma.
We were extremely interested in microorganisms present in the vaginal flora of patients with subchorionic hematoma in the second trimester. The positive rate of Gardnerella vaginalis in vaginal flora of patients with subchorionic hematomas was significantly higher than that of controls. The negative rate of Lactobacillus in patients with subchorionic hematoma was significantly higher than that of the controls. The presence of these organisms in the vaginal flora could indicate the presence of bacterial vaginosis.
Bacterial vaginosis is a condition in which the normal lactobacilli-predominant vaginal flora is replaced with a mixed flora that includes Gardnerella vaginalis, Mycoplasma hominis and anaerobes such as Mobiluncus spp. and Bacteroides spp. The diagnostic criteria were reported by Nugent12 and Amsel.13 Nugent presented a standardized point scoring system based on the presence of three bacterial morphotypes. Amsel demonstrated a combined clinical and laboratory method. In this study, we only investigated whether Chlamydia trachomatis and aerobic microorganisms were present in the vaginal flora. We did not investigate other microorganisms, such as anaerobes, or variable factors of vaginal discharge for bacterial vaginosis criteria; therefore, we could not determine whether bacterial vaginosis was present in the patients.
Bacterial vaginosis has been associated with an increased risk of preterm delivery,14 premature rupture of membranes,15 amniotic fluid infection16 and chorioamnionitis.17 The adverse outcomes of bacterial vaginosis are similar to those of subchorionic hematoma. This suggests that adverse pregnancy outcomes and subchorionic hematomas may be affected by bacterial vaginosis.
In this study, the positive rate of coagulase-negative staphylococci in the vaginal flora of patients with subchorionic hematoma was also significantly higher than that of controls. We suppose that the presence of staphylococci is also related to the development of subchorionic hematoma.
Some previous studies showed that blood coagulation disorders, autoimmune disease and immunological factors were associated with the development of subchorionic hematoma.18–21 No reports demonstrated that vaginal microorganisms were associated with the development of subchorionic hematoma; therefore, this study might be a first step in determining the etiology of subchorionic hematoma.
The vaginal samples were obtained from patients with viable fetuses in the second trimester. At first detection of subchorionic hematoma, the mean gestational age was the first trimester; therefore, we cannot suggest that the vaginal flora defined in this study is directly related to the onset of subchorionic hematoma. It is not clear which bacterial vaginosis is the cause or result of subchorionic hematoma; however, if bacterial vaginosis is a major cause of the development of subchorionic hematomas, early treatment for this may prevent the onset or progression of subchorionic hematomas.