Ultrasonic characteristics of subchorionic hematoma and its effect on pregnancy

LI Yue-ping, YAN Qing-feng, WANG Li, HU Chun-xia✉

1.School of Basic Medicine and Life Science, Hainan Medical University, Haikou 571199, China

2.Department of Obstetrics, The First Affiliated Hospital of Hainan Medical University, Haikou 571199, China

Keywords:

ABSTRACT

Subchorionic hematoma(SCH) is caused by partial detachment of the chorionic membrane from the uterine wall, and blood accumulates between the chorionic membrane and the decidua.Subchorionic hemorrhage is another common term for subchorionic haematomas.Patients maybe experience vaginal bleeding when bleeding from the dissected surface enters the uterine cavity.Subchorionic hematomas are a common cause of vaginal bleeding in patients between 10 to 20 weeks of gestation, with reports showing an incidence between 4% and 22%, most likely due to differences in population, ultrasound equipment and methods, diagnostic criteria,or gestational age in different study[1].

The purpose of this paper is to analyze and summarize the ultrasonographic characteristics of SCH and its impact on pregnancy reported in China and abroad, with a view to helping clinicians to understand SCH.

1.Ultrasound features of the SCH

1.1Size

Ultrasound measurement of hematoma size has equal value in judging prognosis and monitoring of therapeutic effect.There are two ways to grade the SCH size during the ultrasound examination.One uses the subjective grading method[2].That is, the subjective estimation of the proportion of hematoma to gestational sac(applicable to 6～11 weeks), 10% is small hematoma, 11%～25%is small medium hematoma, 26%～50% is medium hematoma,and＞ 50% is large hematoma; or using the ratio of hematoma to gestational sac circumference, small hematoma is generally less than 1/3 of the gestational sac circumference, medium hematoma refers to the proportion of 1/3～2/3, and larger hematoma is greater than 2/3.Another method is more objective, namely, measuring the size of the hematoma and gestational sac before 12 weeks of gestation[3]: Under ultrasound, SCH size = (transverse diameter× front and rear diameter × longitudinal diameter) cm3×0.52;gestational sac size = (transverse diameter longitudinal diameter)cm3×0.52; the size of SCH is determined by the ratio of hematoma to gestational sac, which mild is ＜ 20%, moderate is between 20%to 50%, and severe ＞ 50%.Ayser Hashem’s Clinical study[4] showed that: in SCH patients, most pregnant women with medium or small hematoma, 42% and 35%, respectively, and large hematoma accounted for only 23%.

1.2 Location

It is not difficult to determine the location of hematoma under ultrasound, and understanding the location of hematoma occurrence is very important for clinical prognosis.According to the definition of SCH, SCH contains two conditions: retroplacental hematoma and marginal placental hematoma.The location of the retroplacental hematoma is located between the decidua baslis and the placental chorion, mainly due to the spasm or sclerosis of spiral arterioles in decidua baslis, causing ischemia and necrosis of the distal capillaries,resulting in rupture and bleeding, blood flow accumulating between the decidua baslis and the placenta, leading to the separation of the placenta from the uterine wall.In typical case B ultrasound shows:① placenta thickening; ② villus plate bulge into the amniotic cavity;③ dark area and irregular light mass alternatively emerging behind the placenta, a large attenuation area in the placenta, often forming a large hematoma after the placenta, lifting the placenta up[5].

Marginal hematoma can be seen in the unechogenic area at the edge of the placenta under ultrasound, the hematoma extends under the chorion, the large marginal hematoma echo can be presented as a mixed mass, and the internal punctate echo has rolling phenomenon in the rotating position[6,7].Marginal SCH may be caused by venous rupture at the placental margin.

Ayser Hashem[4] found[4]retroplacental hematoma is very common in patients with SCH during early pregnancy, accounting for about 60%, followed by marginal hematoma, accounting for about 40%.Domestic literature reports that in second trimester, retroplacental hematoma is also more common than marginal hematoma, with the former incidence is about 52%, while the latter is about 48%[8].Compared with marginal hematomas, the retroplacental hematoma is significantly associated with an increased risk of adverse obstetric outcomes, such as fetal distress, stillbirth, NICU admission rates,and preterm birth[8,9]...Rretroplacental hematoma greater than 50mL is often indicative of a poor fetal prognosis[10].

Marginal hematoma has a special situation, also need special attention, namely chronic marginal hematoma which often leads to hemoglobin and its degradation products entering the amniotic cavity, thus causing diffuse chorionic amniotic hemosiderosis(DCH), clinically called chronic placental abruption, pregnancy with DCH is closely related to premature birth and neonatal respiratory diseases[9].

The location of the hematoma is also closely related to the location of the placenta.For example, when the placenta completely occupies the posterior wall of the uterus, the hematoma will be more likely to be located in the lateral wall and the anterior wall of the uterus.Domestic research speculated[11] that the retroplacental hematoma in uterine body or the bottom of the uterus may lead to placental dysfunction.

1.3 Morphology

SCH mostly shows the crescent, triangular, ring or polygonal fluid anechoic area between the uterine wall and the chorion or in the endometrial cavity, mostly parallel to the gestational sac[12].

1.4Outcome

The outcome of SCH is related to pregnancy time.Ayser Hashem[4]observed that most SCH gradually disappeared with pregnancy progression, with 2% of the[4]retroplacental hematomas persisting until the second trimester.Xiang[8] also confirmed that the incidence of SCH persisting until delivery is very low, about 0.46%.Most of the SCH will be gradually absorbed in the later monitoring and treatment.

2.Diseases identified with SCH

SCH under ultrasound sometimes shows different types of echo, which easily causes missed diagnosis or misdiagnosis.Compared with the echo of the uterine wall, there are four types of hematoma echo under ultrasound: anechecho, hypoecho, isoecho and hyperecho.In order to better show the characteristics of the hematoma under ultrasound, multi-angle and multisectional exploration should be performed in transverse section, oblique section and longitudinal section.Some anechoic haemomas can see septal or tube-like membranous structures during exploration.Some hematomas are easy to be missed under ultrasound, such as hypoechoic hematoma will be recognized as amniotic fluid, and other echoic hematoma, easy to be mistaken for the myometrium,hyper-echoic hematoma will be recognized as the placenta[13].When SCH is found, it is necessary to record the number and size at the same time, observe the lesion boundary, internal echo and blood flow, and save the image in real time for later analysis.SCH needs to be distinguished from chorionic uplift under ultrasound, which can represent hematoma or local hemorrhage, or villous or decidua edema.However, no pathological specimens after abortion or surgery can confirm the pathological results consistent with chorionic uplift,and there is no clear etiology[14].Among the 25 domestic cases of misdiagnosed chorionic uplift reported by Chang Junjie et al., 10 of them were diagnosed with SCH.The ultrasound of the former shows that the chorionic decidua surface is irregularly tuberous-like convex to the gestational sac, and the internal echo of the bulge is uniform or uneven, mainly with a slightly lower echo, and the peripheral echo is slightly higher, and the blood flow signal can not be detected within the lesion[15].

3.Effect of SCH on pregnancy

The etiology and pathology of the occurrence of SCH are currently unknown.By analyzing the clinical characteristics of pregnant women with SCH, it seems that SCH is more likely to occur in the pregnant women with uterine damage[16], coagulation disorders[17],positive autoantibodies[18] or conceive by IVF technology[19].Whether systemic disease, or local uterine injury, the occurrence of SCH often suggests the existence of potential placental dysfunction.Long-term clinical observations have found a high correlation between SCH and the occurrence of pregnancy complications,such as abortion, prematurity, and placental abruption, and here we discuss the universally recognized pregnancy complications related to SCH.

3.1 Abortion

Several literature meta-analyses of domestic and abroad showed that the abortion rate of SCH was about 8.9% to 17.6%, and the OR values or RR values were 2.18 and 1.83, respectively, showing a moderate degree of association[17,20].Some scholars believe that the size of the hematoma is related to the risk of abortion, because the small or moderate size of the SCH often subsides, but the large hematoma can cause at least 30 to 40% of the placenta to peel from the uterine wall, and may further expand, thus leading to spontaneous abortion[21].Relevant studies supporting this view show that the abortion rate of large hematoma in early pregnancy is 65.2%,that of medium hematoma is 9.5%, and that of small hematoma is only 2.9%[4].However, the clinical findings show that the above views are not completely consistent with clinical practice, because the hematoma size is affected by the following factors:(1) whether there is vaginal bleeding (2) the speed of intrauterine bleeding (3)the time interval between acute bleeding and ultrasound examination.Therefore, as emphasized by Maso et al[22], We should pay more attention to the presence of the hematoma and whether the location of the hematoma damage the structure and function of the placenta,which is more important than simply considering the hematoma size to determine the pregnancy outcome.In addition, the risk of abortion needs to consider the location of the hematoma.Retroplacental hematoma has been found to be more prone to cause abortion than marginal hematoma.Compared with hematomas near the cervix,the risk of miscarriage and premature delivery of SCH in the uterine body or fundus is increased.Chen Wanyi’s study[23] also supports the above view, believing that the abortion rate of the retroplacental hematoma is significantly higher compared with the marginal subchorionic hematoma (P ＜0.05).

3.2 Preterm birth

It is reported abroad that the premature delivery rate of pregnant women with SCH is about 10.1%～13.6%, and the OR value or RR value is 1.40[20] and 1.76[4] respectively, showing a weak to moderate correlation.The premature delivery rate of SCH in China was 17.9%and that of the control group is 7.2%, with a significant difference[24].The effect of the hematoma location on premature delivery still needs to be considered, because the retroplacental hematoma was found to be associated with a lower 1-minute Apgar score (RR= 1.67).This may be due to the placental infarction caused by the maternal uterine spiral artery angiopathy due to the retroplacental hematoma, or hematoma affecting uterine-placental blood flow,resulting in impaired placental function, coupled with continuous contractions leading to the occurrence of preterm birth[8].Wang Juan’s study[7] found that the preterm birth rate of retroplacental hematoma (23.2%) was significantly higher than that of marginal subchorionic hematoma (7.8%), and there was a significant difference (P ＜0.05).

3.3 Placental abruption

In the Tuuli MG’s SCH meta-analytical literature[20], study showed that SCH increased the risk of placental abruption, with an incidence of about 0.7% to 3.6%, and an OR value of 5.71, showing a strong association.This is due to the presence of the hematoma, especially the retroplacental hematoma, which may cause further separation of the placenta from the uterine wall and leading to placental abruption.In general, placental abruption (PA) is more common after 16 weeks of gestation, including placental or periplacental bleeding[25].The highest incidence of placental abruption is 24-26 weeks of gestation,after which the incidence decreases with increasing gestational age[26].Placental abruption triggers a series of subsequent issues to consider, including cesarean section, blood transfusion, disseminated intravascular coagulation (DIC), hypovolemic shock, hysterectomy,renal failure, and maternal death[27].Fetal complications include fetal distress, intrauterine fetal growth restriction, or intrauterine fetal death.Neonatal complications include neonatal death, prematurityrelated complications, etc.

3.4 Fetal intrauterine growth restriction

Ayser Hashem’s study[4] found that the RR value of SCH and fetal intrauterine growth restriction (IUGR) was 3.17, showing a strong association.The mechanism of IUGR is uterine and placental insufficiency.While focusing on the impact of SCH size and location on placental function, we also cannot ignore the occurrence of SCH due to developmental defects of the placenta itself or macrofacial thrombosis and leading to placental insufficiency.Chih-Ping Chen[28]reported a case of SCH complicated with IUGR which conducted the normal fetal appearance and chromosome examination, showed the multiple grape, dilated and curved subchorionic vessels; microscopic examination showed dilated villi, blocked vessels, thrombosis and bleeding.

3.5 Premature rupture of membranes

The risk probability value of premature rupture of membranes(PROM) in the SCH population is 2.3% to 3.8%, and the OR value is 1.64, showing a moderate degree of association[20]; The SCH leading to PROM mostly occurs at the edge of the placenta or behind the chorion, and the hematoma at these sites may cause dominant vaginal bleeding, and the inflammation may degrade the membranes, lead to PROM, which may also directly stimulate the myometrium, leading to preterm birth[21]; It is worth noting that the PROM triggered by SCH is not always dominant, and sometimes may be insidious, and in cases of SCH and pathological DCH,hemolytic products can cause DNA oxidative damage in amniotic epithelial cells, resulting in abnormal amniotic fluid distribution or occult PROM, manifested by oligohydramotic fluid[29].

3.6 Stillbirth and stillborn foetus

Ayser Hashem’s study[4] found that the chance of stillbirth in SCH pregnant women is about 0.9% to 1.9%, and its OR value is 2.09,which is also a moderate degree of association[8].Recent foreign studies have demonstrated the correlation between the degree of placental dissection and pregnancy outcomes;This prognosis is better if only marginal placental dissection is present, because, the affected placental area is small and has no substantial effect on the fetus.Fetal hypoxia is further exacerbated when the hematoma causes persistent contractions or when the hematoma itself affects local uterine blood flow and placental dysfunction, which may be the main cause of fetal death due to placental abruption.

In conclusion, we explored some manifestations of SCH under ultrasound and the impact of SCH on pregnancy, and clinicians can prejudge and handle the possible complications of pregnancy according to the different characteristics of SCH.As the etiology and pathological mechanisms of SCH are not very clear, we need to further explore the clinical characteristics of SCH and its high-risk factors in the future clinical research work.