Low-lying placenta

Low-lying placenta is a common form of abnormal pregnancy. Low-lying placenta can cause bleeding in late pregnancy. Low-lying placenta can be said to be the most serious complication in late pregnancy. If the low-lying placenta is not handled properly, it will not only affect the healthy growth of the fetus, but also affect the lives of mother and child. However, the incidence of low-lying placenta is not high, so mothers do not need to have too much psychological pressure.

The harm of a low-lying placenta is so great, so what are the factors that cause a low-lying placenta? What should a pregnant woman do if she finds that her placenta is low-lying? Let the gynecologist take you to fully understand the basic knowledge of a low-lying placenta.

A low-lying placenta is also called placenta previa.

The normal attachment site of the placenta is on the posterior, anterior or lateral wall of the uterine body. If the placenta is attached to the lower part of the uterus or covers the internal os of the cervix and is lower than the presenting part of the fetus, it is called placenta previa. Placenta previa is one of the main causes of bleeding in late pregnancy and a serious complication during pregnancy. If not handled properly, it can endanger the lives of mother and child. The incidence rate is 1:55 to 1:200, and it is more common in multiparous women, especially multiparous women.

1. Causes

It is not yet clear. It may be related to the following factors: ① Imperfect endometrium. Postpartum infection, multiple births, IUD insertion, multiple curettage and curettage, cesarean section and other surgeries can cause endometritis, endometrial defects and insufficient blood supply. In order to absorb sufficient nutrients, the placenta compensatorily expands its area and extends to the lower segment of the uterus. ② The fertilized egg develops slowly, and when it reaches the uterine cavity, the trophoblast has not yet developed to the stage where it can implant, so it continues to be transplanted into the lower segment of the uterus. ③ The placenta area is too large. For example, most gestational discs often extend to the lower part of the uterus, forming placenta previa.

2. Classification

Placenta previa is divided into three types based on the relationship between the placenta edge and the cervix.

⑴ Complete placenta previa ⑵ Partial placenta previa ⑶ Low-lying placenta previa

(a) Complete placenta previa or central placenta previa, the internal cervical os is completely covered by placental tissue.

(B) Partial placenta previa: The internal cervical opening is partially covered by placental tissue.

(III) Marginal placenta previa: The placenta is attached to the lower segment of the uterus, with the edge close to but not exceeding the internal os of the cervix.

The relationship between the edge of the placenta and the internal os of the cervix changes with the disappearance of the cervical canal and the gradual expansion of the cervical os. In principle, the relationship between the two at the time of admission is used as the standard for diagnosing various types of placenta previa, which is conducive to formulating treatment plans.

3. Clinical manifestations

Painless, recurrent vaginal bleeding in late pregnancy or during labor is the main symptom of placenta previa, which occasionally occurs at 20 weeks of pregnancy. Bleeding is caused by the gradual stretching of the lower uterine segment in late pregnancy or after labor, the disappearance of the cervical canal, and the expansion of the cervical opening. The placenta attached to the lower uterine segment or the internal opening of the cervix cannot stretch accordingly, so that the anterior part of the placenta is detached from its attachment point, causing the blood sinus to rupture and cause bleeding. Bleeding is frequent without any cause. The early or late occurrence of vaginal bleeding, the number of recurrences, and the amount of bleeding are closely related to the type of placenta previa. The first bleeding of complete placenta previa often occurs early, around 28 weeks of pregnancy, and the bleeding is frequent and the amount is large. Sometimes a single large amount of bleeding can put the patient into shock. The first bleeding of marginal placenta previa occurs later, usually between 37 and 40 weeks of pregnancy or after delivery, and the amount is also less. The time of first bleeding and the amount of bleeding of partial placenta previa are between the two. With each contraction after labor, the lower segment of the uterus is pulled upward and bleeding often increases. In patients with partial and marginal placenta previa, if the fetal presenting part can descend quickly after rupture of membranes and directly compress the placenta, bleeding can stop. Rupture of membranes facilitates compression of the placenta by the presenting fetus. Due to repeated or heavy vaginal bleeding, the mother may develop anemia, the degree of which is proportional to the amount of bleeding. Severe bleeding may cause shock, and the fetus may suffer from hypoxia, distress, and even death.

4. Diagnosis

(A) Medical history: Sudden onset of painless, recurrent vaginal bleeding in late pregnancy is suspected to be placenta previa. If the bleeding starts early and the amount is heavy, it is likely to be complete placenta previa.

(B) Physical signs vary depending on the amount of blood loss. There may be multiple bleeding episodes, anemia, acute massive bleeding, and shock. Abdominal examination is the same as that of a normal pregnancy. Excessive blood loss causes fetal intrauterine hypoxia and distress. In severe cases, the fetus may die in utero. For women in labor who have paroxysmal uterine contractions and hear a blowing murmur above or on both sides of the pubic symphysis that is consistent with the maternal pulse, the placenta may be located in front of the lower uterine segment. If it is located at the back, no placental blood flow murmur will be heard.

(III) Vaginal examination generally consists of vaginal peepal and fornix palpation, and arbitrary digital examination of the endocervical canal should be avoided. It can only be performed under the conditions of infusion, blood transfusion and surgery. If the diagnosis is clear or bleeding is excessive, there is no need for a vaginal examination. Type B ultrasound examination is now used, and vaginal examination is rarely performed.

(IV) Ultrasound examination: B-type ultrasound tomographic images can clearly show the uterine wall, fetal head, cervix and placenta, and the type of placenta previa can be further determined based on the relationship between the edge of the placenta and the internal os of the cervix. The accuracy rate of placental positioning is over 95%, and it can be checked repeatedly. It has been adopted both at home and abroad in recent years, and has basically replaced other methods.

When diagnosing placenta previa with B-type ultrasound, the gestational age must be noted. In mid-pregnancy ultrasound examinations, approximately 30% of the placentas are located low, exceeding the internal os. As the pregnancy progresses, the lower uterine segment is formed, the uterine body rises, and the placenta moves upward accordingly. Therefore, if a low-lying placenta is found during a mid-pregnancy ultrasound examination, do not make a diagnosis of placenta previa too early. It must be combined with clinical considerations. If there are no bleeding symptoms, do not diagnose placenta previa before 28 weeks.

(V) Postpartum examination of the placenta and fetal membranes For patients with antepartum hemorrhage, the delivered placenta should be carefully examined during delivery to verify the diagnosis. The anterior part of the placenta has old blood clots attached and appears black and purple. If these changes are at the edge of the placenta and the rupture of the fetal membrane is less than 7 cm away from the edge of the placenta, it is a low-lying placenta.

5. Differential Diagnosis

Bleeding in late pregnancy is mainly differentiated from early placental abruption. Prenatal bleeding caused by other reasons, such as rupture of velamentous placental vessels anteriorly, rupture of placental marginal sinuses and cervical lesions such as polyps, erosions, and cervical cancer, can be diagnosed through vaginal examination, ultrasound examination and placental examination after delivery combined with medical history.

6. Impact on Mother and Child

(1) Postpartum hemorrhage: After delivery, the muscle tissue in the lower segment of the uterus is thin and has poor contraction force. After the placenta attached to this segment is detached, the blood sinuses are not easy to contract and close for a while, so postpartum hemorrhage often occurs.

(B) Placenta accreta: The placental villi can be implanted into the myometrium due to reasons such as uterine decidua hypoplasia. Placenta previa is occasionally complicated by placenta accreta, in which the placenta is implanted in the myometrium of the lower uterine segment, resulting in incomplete placental separation and heavy bleeding.

(3) Postpartum infection: The placental detachment surface of placenta previa is close to the external cervical os, and bacteria can easily invade the placental detachment surface from the vagina. In addition, the mother is anemic and has a weak constitution, so infection is prone to occur.

(IV) Increased premature birth and perinatal mortality. Placenta previa bleeding mostly occurs in the late pregnancy and can easily lead to premature birth. The perinatal mortality rate of placenta previa is also high. The fetus may die in utero due to maternal shock, intrauterine distress, severe hypoxia, or die after birth due to poor vitality of premature birth. In addition, during vaginal operation or before cesarean section, the placenta is damaged and the lobules rupture, which can cause fetal blood loss and neonatal asphyxia.

VII. Prevention

Promote contraception, implement family planning, prevent multiple births, avoid multiple curettages or uterine cavity infections, and avoid endometrial damage or endometritis. Strengthen prenatal examinations and education. For bleeding during pregnancy, no matter how much bleeding, you must seek medical attention in time to achieve early diagnosis and correct treatment.

A low-lying placenta is very harmful to the health of the mother and the fetus, so it is very important to do a good job of prevention. Multiple miscarriages and uterine infections should be avoided in daily life. At the same time, if the placenta is low-lying, you must go to a regular hospital for treatment. If necessary, you must give up the child's life to save the mother's life.