Painless, recurring vaginal bleeding in the third trimester or during labor

Introduction In the third trimester or at the time of labor, painless repeated vaginal bleeding is the main symptom of the placenta previa. The normal placenta is attached to the posterior, anterior or side wall of the uterus. If the placenta is attached to the lower part of the uterus, and even the lower edge of the placenta reaches or covers the inner opening of the cervix, its position is lower than the first exposed part of the fetus, called the placenta previa. Placenta previa is one of the main causes of late pregnancy bleeding, and is a serious complication during pregnancy. Improper handling can endanger the safety of mother and child. The incidence rate is 0.24% to 1.57% in domestic reports and 1.0% in foreign countries. 85% to 90% of patients with placenta previa are maternal, especially multi-partum, with a prevalence of up to 5%.

Cause

(1) Causes of the disease

The cause is not completely clear, but after extensive research by scholars at home and abroad, it has been initially determined that it may be related to the following factors.

Endometrial lesions and injuries

(1) Relationship between induced abortion and placenta previa: Abortion has been reported to increase the incidence of placenta previa by 7 to 15 times. It has also been confirmed that the rate of placenta previa is 4.6% after abortion. Artificial abortion curette or human flow attraction can damage the endometrium, causing the formation of intimal scars, and then the decidual dysplasia during pregnancy, so that the pregnant eggs are planted down; or the factor of endometrial blood supply is insufficient, in order to obtain more blood For feeding and nutrition, the placenta area is increased, resulting in a placenta previa. Many domestic research reports have confirmed the correlation between abortion and placenta previa, and the more frequent abortions, the higher the incidence of placenta previa.

(2) Relationship between cesarean section and placenta previa: The incidence of placenta previa in the history of cesarean section was 5.95 times that of cesarean section. Miller et al reported in 1996 that the incidence of placenta previa with a history of cesarean section was three times higher than that without cesarean section. Moreover, the incidence of placenta previa was increased by 1.9% and 4.1% in pregnant women who had undergone cesarean section twice or more, and the conclusion was that the incidence of placenta previa increased with the number of previous cesarean sections. Also increased. On the contrary, some scholars hold different views. Although the risk of placenta previa is increased in pregnant women with a history of cesarean section, the risk does not increase with the increase in the number of cesarean sections. Although the mechanism of the increase in the incidence of placenta previa in previous cesarean section is not clear, some hypotheses have been proposed. If some scholars believe that the previous cesarean section of the classical or lower uterus incision, scar formation in the longitudinal direction of the uterus or the lower part of the uterus, the poor supply of blood to the local decidua during the second pregnancy may easily lead to the occurrence of the placenta previa. It has also been suggested that scarring of the lower uterus may somehow attract the placenta or the placenta adheres to the lower uterus, resulting in an increased incidence of placenta previa and a greater chance of placenta implantation.

(3) The relationship between maternal age and placenta previa: Many scholars have found that the incidence of placenta previa increases with the increase of the age of pregnant women. Physiologically, as women age, the more normal muscle components of collagen replacing the myometrial artery wall. Some scholars have also found that the percentage of intrauterine arteries with sclerosing lesions is different at different ages. For example, at the age of 17 to 19, only 11%; at 20 to 29, 37%; at 30 to 39, 61%; and after 39, 83%. These vessel wall lesions can limit the expansion of the arterial lumen, which in turn affects the blood supply to the placenta and manifests as a defect in vascular development on the diaphragm. These conditions are presumed to play an important role in the development of placenta previa in elderly women.

(4) Relationship between birth and placenta: The placenta previa is widely recognized in the past. Some scholars believe that the endometrial damage of the placenta implant site can be caused by each pregnancy regardless of the outcome. As a result, the placenta is implanted in the next pregnancy, and the part of the placenta is displaced to the lower part of the uterus. It is also considered that repeated pregnancy causes the endometrial blood supply to be reduced in these parts, so that the villus gap is sufficient for re-pregnancy. Blood supply must increase the area of placenta attachment, which increases the risk of placenta previa.

In short, these factors cause endometritis or endometrial damage, resulting in uterine decidual growth, when the fertilized egg is implanted, the blood supply is insufficient, in order to get enough nutrition, the placenta stretches to the lower part of the uterus.

2. Excessive placenta area and abnormal placenta: abnormal placental size, such as in twin or multiple pregnancy, the area of the placenta is larger than the area of a single child and reaches the lower part of the uterus. It is reported that the incidence of placenta previa of twins is higher than that of single birth. Doubled. Abnormal placenta morphology, mainly refers to the paraplacenta, membranous placenta, etc., when the placenta, the main placenta is in the uterine body, and the secondary placenta can be located in the lower part of the uterus near the cervix. The membranous placenta is large and thin, with a diameter of 30 cm, and can be extended to the lower uterus. The reason may be related to the fact that the embryo sac is planted deep in the endometrium, which makes the velum villi persist.

3. Smoking: Many studies have shown that smoking in pregnant women increases the risk of developing placenta previa. Williams and other studies have found that the risk of placenta previa in pregnant women is twice as high. There are also reports that the number of cigarettes has a significant correlation with the occurrence of placenta previa. The probability of a placenta previa is 0.8 when the number of cigarettes is <10 per day. When the amount of smoking is >40 per day, the placenta previa occurs. The probability is 3.1. Regarding the mechanism of its occurrence, it is considered that the exposure to nicotine and carbon monoxide in pregnant women causes hypoxemia, which causes placental hypertrophy, thereby increasing the risk of placenta planting in the lower uterus, leading to the occurrence of placenta previa.

an examination

Related inspection

Obstetric B super obstetric examination blood routine amniotic fluid bilirubin amniotic fluid bilirubin

History

In the third trimester of pregnancy or during labor, there is no painful repeated vaginal bleeding. It should be considered as the placenta previa. If the bleeding is early and the amount is high, the possibility of complete placenta previa is large.

2. Signs

According to the amount of blood loss, multiple bleeding, anemia, acute massive bleeding, shock can occur. Except for the first exposure of the fetus, the abdominal examination is the same as normal pregnancy. Excessive blood loss can occur in the fetal intrauterine hypoxia, severe cases of fetal death. Placental murmurs can sometimes be heard above the pubic symphysis, but are not heard when the placenta is attached to the posterior wall of the lower uterine segment.

3. Vaginal examination

Generally only for vaginal peeping and ankle percussion, should not be diagnosed in the neck tube, so as not to cause the placenta attached to the place to cause large bleeding. If it is a complete placenta previa, it is even life-threatening. A vaginal examination is used to confirm the diagnosis and determine the mode of delivery before termination of pregnancy. It must be carried out under conditions of infusion, blood transfusion and surgery. If the diagnosis is clear or excessive bleeding, no vaginal examination should be performed. In recent years, B-mode ultrasound has been widely used, and vaginal examinations have rarely been done.

Inspection Method

After strict disinfection of the vulva, use a vaginal speculum to observe the presence or absence of varicose veins, cervical polyps, cervical cancer or other lesions that cause bleeding. After peeping, use one hand and two fingers to gently palpate the vaginal canal around the cervix. If the sputum is clearly removed, the placenta can be removed. If there is a difference between the finger and the first dew Thick soft tissue (placenta) should be considered as a placenta previa. If the cervix has been partially dilated and there is no active bleeding, the index finger can be gently inserted into the cervix to check for the presence or absence of a sponge-like tissue (placenta), if the blood clot is brittle. Note the relationship between the edge of the placenta and the cervix to determine the type of placenta previa. If the membrane is touched and the membrane is broken, the membrane can be pierced. Be gentle and do not separate the placenta tissue from the attachment to avoid major bleeding. If major bleeding occurs during the examination, the examination should be stopped immediately and the cesarean section should be performed to end the delivery.

Ultrasonography

B-mode ultrasound tomography can clearly see the location of the uterine wall, the exposed part of the fetus, the placenta and the cervix, and further clarify the type of placenta previa based on the relationship between the edge of the placenta and the internal cervix. The accuracy of placenta positioning is over 95%, and it can be repeatedly checked. It has been widely used at home and abroad in recent years, basically replacing other methods, such as radioisotope scanning and localization, indirect placental angiography.

B-mode ultrasound diagnosis: attention should be paid to the number of gestational weeks when the placenta is placed in the placenta. The placenta in the second trimester occupies half of the uterine cavity. Therefore, the placenta has more chances in the inner cervix or the inner mouth. By the late pregnancy, the placenta accounts for 1/3 or 1/4 of the uterine cavity. At the same time, the formation and extension of the lower uterus increases the internal cervix and the placenta. The distance between the placenta, which seems to be in the lower part of the uterus, can change to the normal placenta with the uterus moving up. Therefore, if mid-pregnancy B-mode ultrasound findings of low placenta position, do not premature diagnosis of placenta previa, should be followed up regularly without vaginal bleeding symptoms, 34 weeks before pregnancy is generally not diagnosed with placenta previa.

5. Postpartum examination: placenta and fetal membranes for patients with prenatal bleeding, the placenta should be carefully examined after delivery to verify the diagnosis. The placenta in the front part has black and purple old blood clots attached. If the distance between the membrane and the edge of the placenta is <7cm, it is a partial placenta previa.

Differential diagnosis

Late pregnancy bleeding should be differentiated from placental abruption: antenatal hemorrhage due to other causes, such as rupture of the anterior vessel of the placenta, rupture of the sinusoids at the edge of the placenta, and cervical lesions such as polyps, erosion, cervical cancer, etc. B-mode ultrasonography and placenta examination after delivery can confirm the diagnosis.

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