Placenta previa is an anomaly of the pregnancy period characterized by the attachment of the placenta to the lower segment of the uterus with partial or complete overlap of the internal uterine pharynx. Clinically, placenta previa is manifested by recurrent bleeding from the genital tract, anemia of a pregnant woman, the threat of miscarriage, fetal-placental insufficiency. Placenta previa is diagnosed during vaginal examination, ultrasound. Detection requires prevention of spontaneous termination of pregnancy, correction of anemia and fetal hypoxia, selection of optimal delivery tactics (more often – cesarean section).
ICD 10
O44 Placenta previa
General information
The placenta (the afterbirth, the baby’s place) is an important embryonic structure, tightly adjacent to the inner wall of the uterus and providing contact between the organisms of the mother and fetus. During pregnancy, the placenta performs nutritional, gas exchange, protective, immune, hormonal functions necessary for the full development of the embryo and fetus. Physiological is considered to be the location of the placenta in the area of the posterior and lateral walls of the body or the bottom of the uterus, i.e. in the areas of the best vascularization of the myometrium. The attachment of the placenta to the posterior wall is optimal because it protects this embryonic structure from accidental damage. The location of the placenta on the anterior surface of the uterus is rare.
If the placenta is attached so low that it overlaps the inner pharynx to a certain extent, they talk about placenta previa. In obstetrics and gynecology, placenta previa occurs in 0.1-1% of all births. With the total closure of the internal pharynx by the placenta, there is a variant of complete placenta previa. This type of pathology occurs in 20-30% of the number of presentations. With partial overlap of the internal pharynx, the condition is regarded as incomplete placenta previa (frequency 35-55%). When the lower edge of the placenta is localized in the third trimester at a distance of less than 5 cm from the inner pharynx, a low placenta location is diagnosed.
Placenta previa creates conditions for prematurity and fetal hypoxia, incorrect position and presentation of the fetus, premature birth. The proportion of perinatal mortality with placenta previa reaches 7-25%, and maternal mortality due to bleeding and hemorrhagic shock – 3%.
Causes
Placenta previa is more often caused by pathological changes in the endometrium, disrupting the course of the decidual stroma reaction. Such changes can be caused by inflammation (cervicitis, endometritis), surgical interventions (diagnostic curettage, surgical termination of pregnancy, conservative myomectomy, cesarean section, perforation of the uterus), multiple complicated childbirth.
The etiological factors of placenta previa include endometriosis, uterine fibroids, uterine abnormalities (hypoplasia, bicornuate), multiple pregnancies, cervical canal polyps. Due to these factors, the timeliness of implantation of the fetal egg in the upper parts of the uterine cavity is disrupted, and its attachment occurs in the lower segments. Placenta previa develops more often in repeatedly pregnant women (75%) than in primiparous women.
Placenta previa symptoms
In the placenta previa clinic, the leading manifestations are repeated uterine bleeding of varying severity. During pregnancy, bleeding caused by placenta previa is recorded in 34% of women, during childbirth – in 66%. Bleeding can develop at different stages of pregnancy – from the first trimester to the very birth, but more often – after 30 weeks of gestation. On the eve of childbirth, due to periodic contractions of the uterus, bleeding usually increases.
The cause of bleeding is a repeated detachment of the adjacent part of the placenta, which occurs due to the inability of the placenta to stretch after the uterine wall during pregnancy or labor. With detachment, there is a partial opening of the interstitial space, which is accompanied by bleeding from the vessels of the uterus. At the same time, the fetus begins to experience hypoxia, since the detached part of the placenta ceases to participate in gas exchange. With placenta previa, bleeding can be provoked by physical exertion, coughing, sexual intercourse, straining during defecation, vaginal examination, thermal procedures (hot bath, sauna).
The intensity and nature of bleeding is usually determined by the degree of placenta previa. The complete presentation of the placenta is characterized by the sudden development of bleeding, the absence of pain, and the abundance of blood loss. In the case of incomplete placenta previa, bleeding, as a rule, develops closer to the time of delivery, especially often – at the beginning of labor, during the period of smoothing and opening of the pharynx. The greater the degree of placenta previa, the earlier and more intense the bleeding is. t. a., bleeding during placenta previa is characterized by an external character, sudden onset without apparent external causes (often at night), the release of scarlet blood, painlessness, mandatory repetition.
Recurrent blood loss quickly leads to anemia of the pregnant woman. A decrease in the BCC and the number of red blood cells can cause DIC syndrome and the development of hypovolemic shock, even in the case of minor blood loss. Pregnancy complicated by placenta previa often proceeds with the threat of spontaneous abortion, arterial hypotension, gestosis. The premature nature of childbirth more often occurs with a full presentation of the placenta.
The pathology of the placenta location has the most unfavorable effect on fetal development: it causes fetal-placental insufficiency, hypoxia and delayed fetal maturation. With placenta previa, a pelvic, oblique or transverse position of the fetus is often observed. In the II-III trimesters of pregnancy, the localization of the placenta may change due to the transformation of the lower uterine segment and changes in the growth of the placenta in the direction of better blood-supplied areas of the myometrium. This process in obstetrics is called “migration of the placenta” and is completed by 34-35 weeks of pregnancy.
Diagnosis
When recognizing placenta previa, the presence of risk factors in the history of a pregnant woman, episodes of recurrent external uterine bleeding, and objective research data are taken into account. An external obstetric examination reveals a high standing of the uterine floor due to the location of the adjacent part of the fetus, often a transverse or oblique position of the fetus. During auscultation, the noise of placental vessels is heard in the lower segment of the uterus, at the location of the placenta.
During the gynecological examination, the cervix is examined in mirrors to exclude its injuries and pathology. With the external pharynx closed, it is impossible to establish the adjacent part of the fetus. With full presentation of the placenta, a massive soft formation occupying all the vaults of the vagina is palpated; with incomplete – anterior or one of the lateral arches.
With the patency of the cervical canal in the case of complete presentation, the placenta closes the entire opening of the internal pharynx, and its palpation leads to increased bleeding. If fetal membranes and placental tissue are found in the lumen of the uterine pharynx, incomplete placenta previa is diagnosed. Vaginal examination with placenta previa is performed extremely carefully, in conditions of readiness for emergency care with the development of massive bleeding.
The safest objective method of detecting placenta previa, which is widely used by obstetrics and gynecology, is ultrasound. During the echography, a variant (incomplete, complete) placenta previa is established, the size, structure and area of the adjacent surface, the degree of detachment during bleeding, the presence of retroplacental hematomas, the threat of termination of pregnancy, the “migration of the placenta” is determined in the process of dynamic studies.
Placenta previa treatment
The tactics of pregnancy management with placenta previa is determined by the severity of bleeding and the degree of blood loss. In the I-II trimester, in the absence of spotting, a pregnant woman with placenta previa may be under the outpatient supervision of an obstetrician-gynecologist. At the same time, a protective regime is recommended, excluding factors that provoke bleeding (physical activity, sexual life, stressful situations, etc.).
At a gestation period of more than 24 weeks or the onset of bleeding, pregnancy monitoring is carried out in an obstetric hospital. Therapeutic tactics are aimed at maximum prolongation of pregnancy. Bed rest, drugs with antispasmodic (drotaverine) and tocolytic (phenoterol, hexoprenaline) effects are prescribed, iron deficiency anemia is corrected (iron preparations). In order to improve fetoplacental and uteroplacental blood flow, the administration of pentoxifylline, dipyridamole, ascorbic acid, thiamine pyrophosphate is used. When there is a threat of the onset of premature labor at the period from 28 to 36 weeks of pregnancy, glucocorticoids (dexamethasone, prednisone) are prescribed for the prevention of repiratory disorders in a newborn.
Indications for emergency early delivery are repeated bleeding of over 200 ml, severe anemia and hypotension, bleeding with simultaneous blood loss of 250 ml, bleeding with full placenta previa. In these cases, a caesarean section is performed to save the mother, regardless of the gestation period and the viability of the fetus.
With successful prolongation of pregnancy to 37-38 weeks, the optimal method of delivery is chosen. Cesarean section is indicated absolutely in all cases of complete placenta previa, as well as with incomplete presentation, combined with transverse position or pelvic presentation of the fetus; burdened with obstetric and gynecological history; the presence of a scar on the uterus, multiple pregnancy, polyhydramnios, narrow pelvis.
Natural childbirth is possible only with incomplete placenta previa, provided that the cervix is mature, good labor activity, and fetal head previa. At the same time, the fetal condition and contractile activity of the uterus are constantly monitored (CTG, fetal phonocardiography). In the early postpartum periods, women in labor often have atonic bleeding, lochiometry, ascending infection and metrothrombophlebitis. If it is impossible to conservatively stop massive bleeding, they resort to removal of the uterus: supravaginal amputation or hysterectomy.
Prevention
Preventive measures for placenta previa are prevention of abortions, early detection and treatment of genital pathology and hormonal dysfunction. With the development of placenta previa during pregnancy, early reliable diagnosis of the anomaly is necessary, rational management of pregnancy taking into account all risks, timely correction of concomitant disorders, optimal delivery.
