Complete placenta previa is a variant of placental tissue placement, in which it completely overlaps the internal pharynx of the uterus. It is manifested by painless bloody discharge of varying intensity, occurring mainly in the second half of the gestational period. In the diagnosis, transvaginal ultrasound is used, less often — MRI and vaginal examination. The only possible way of delivery is to perform a caesarean section. With signs of fetal immaturity and stopped bleeding, infusion and antianemic therapy, tocolytics, hemostatics, disaggregants are recommended, according to indications — glucocorticosteroids.
Complete placenta previa is about 0.08% of all pregnancy cases. Pathology is three times more common in re-giving birth patients, in women aged 35 and over. According to domestic statistics, complete presentation of placental tissue is observed in 0.03-0.11% of births. Over the past decades, such obstetric pathology has been more common, which is presumably due to the increased number of intrauterine interventions and abortions. Since with central presentation, the risk of stillbirth reaches 17-26%, the main task of specialists is the timely detection of an anomaly and the choice of optimal management tactics for a pregnant woman.
Causes of Complete placenta previa
Atypical localization of the placenta occurs when it is impossible to implant the fetal egg in the right place. There are two groups of reasons for which the probability of complete presentation increases:
- Uterine factors. Placentation conditions are disrupted by endometrial dystrophy, scarring and poor uterine wall vascularization. Such pathological conditions arise due to chronic and postpartum endometritis, as a result of frequent abortions and other invasive procedures, in the presence of post-traumatic or postoperative scar (after rupture, conservative exfoliation of the myomatous node, etc.).
- Fetal factors. Low activity of fetal egg proteases can provoke nidation with overlapping of the pharynx. This situation is usually caused by erythroblastosis of the fetus and a delay in the development of the embryo due to chromosomal aberrations or hormonal imbalance.
Complete placenta previa is more often diagnosed with multiple pregnancies, in women over 35 years old, pregnant women with frequent childbirth, uterine hypoplasia, bicornular or saddle-shaped uterus. The probability of atypical localization of the placenta increases if there is a similar problem in the past, smoking, the use of certain narcotic substances (e.g., cocaine).
Taking into account the site of the primary implantation of the fetal egg, specialists in the field of obstetrics and gynecology consider two mechanisms for the formation of the placenta previa. In primary isthmic placenta, due to gross morphological changes in the uterine wall or insufficient protease levels, the fertilized egg is initially embedded in the endometrium in the isthmus area. In secondary isthmic placenta, implantation occurs at the bottom of the uterus and only then spreads to the pharyngeal region. At the same time, villi are partially preserved on the decidua capsularis site, a branched, rather than smooth chorion is formed. The further clinical picture is due to the inability of the placental tissue to stretch and the occurrence of bleeding due to the opening of the interstitial spaces during the detachment of the placenta from the uterine wall.
Complete placenta previa corresponds to the III and IV degrees of atypical placenta location according to the results of echographic examination. Taking into account the peculiarities of the placental tissue location in the uterine pharynx , two types of complete presentation are distinguished:
- Asymmetric. At the III degree of presentation (according to ultrasound data), the placenta enters the opposite side of the lower segment, and most of it is located on one of the walls — either anterior or posterior.
- Symmetrical. At grade IV, the central part of the placenta overlaps the uterine pharynx, its tissues are symmetrically located on the walls of the uterine cavity.
Symptoms of complete placenta previa
A typical sign of the overlap of the uterine pharynx with placental tissue is painless bright scarlet discharge from the vagina, which appears from the second trimester. According to the results of observations, approximately one—third of pregnant women with complete placenta previa begin to pick up before the 30th week, one-third – at 33-34 and the remaining third — from 36. The discharge has a different intensity, appears spontaneously at rest or against the background of physical exertion or uterine hypertension. In most patients, before the onset of labor, such bleeding occurs repeatedly and stops on their own. In every fifth woman, the appearance of bleeding is accompanied by a clinic for premature termination of pregnancy — acute cramping pain in the lower abdomen and increased uterine tone.
The most threatening complication of complete placenta previa is its detachment with copious obstetric bleeding, which is often accompanied by the loss of a child and is a threat to the life of a pregnant woman. Significant blood loss is sometimes complicated by hypovolemic shock, DIC syndrome, necrosis of the renal tubules and pituitary gland. Constant blood loss during spontaneous bleeding leads to anemia, placental insufficiency and intrauterine fetal hypoxia. In addition, in such patients, the probability of placental increment, pathological transverse and oblique position of the child, premature rupture of the amniotic sac and the onset of labor, weakness of the birth forces increases.
With timely registration in the antenatal clinic and regular monitoring by specialists, central placenta previa is usually detected long before the appearance of clinical symptoms. For diagnosis, methods are used that allow you to visualize the fetus and its membranes in the uterine cavity, as well as to assess the depth of attachment of the placenta to the uterine wall:
- Transvaginal ultrasound. The accuracy of the method reaches 95%. Vaginal sonography is performed after abdominal ultrasound to clarify exactly how the placenta is located in relation to the cervix.
- MRI of the pelvic organs. It is prescribed in those rare cases when ultrasound examination does not allow an accurate diagnosis. Provides the most accurate visualization of the placenta and the elements of the fetal egg.
Vaginal examination is performed extremely rarely and only in the conditions of an expanded operating room, where in case of increased bleeding, a caesarean section can be performed quickly. During palpation, spongy tissue is determined between the protruding part of the fetus and the fingers of the obstetrician-gynecologist. Fetal cardiotocography is recommended for dynamic assessment of the child’s condition. Presentation is differentiated from ectopic cervical pregnancy, premature detachment of the normally located placenta, erosion, polyp and cervical cancer, damage to the vaginal veins with their varicose veins. With significant anemia and suspicion of systemic blood diseases with increased bleeding, a consultation with a hematologist is indicated. According to the indications, a therapist, an anesthesiologist-resuscitator, a neonatologist are involved in the management of the patient.
Treatment of complete placenta previa
There are no conservative or operative methods for changing the placenta location. Natural childbirth with complete placenta previa is impossible, delivery is carried out by caesarean section. Obstetric tactics are aimed at reducing the risk of premature birth and rapid fetal extraction with the threat of massive bleeding. A patient with suspected complete presentation of placental tissues is subject to urgent hospitalization. If the fetus is premature, there is no labor activity, and spotting has stopped, expectant conservative management is possible. The pregnant woman is transferred to full bed rest with the exception of any physical activity. After the blood loss, the following are indicated:
- Infusion therapy. The appointment of physiological and colloidal solutions allows you to restore the volume of circulating blood and improve its rheological characteristics.
- Antianemic agents. The choice of the drug is determined by the severity of anemia. To maintain the recommended hemoglobin level (from 100 g / l), iron—containing agents are used in mild cases, with significant blood loss – transfusion of blood or its components.
- Drugs that improve hemostasis and microcirculation. If the bleeding is combined with a violation of the clotting function of the blood, the pregnant woman is injected with freshly frozen plasma, platelet mass, disaggregants.
- Tocolytics. Means to reduce hypertonicity of the myometrium are prescribed with caution. With a stable condition and preserved kidney function, magnesium sulfate is most often used.
- Glucocorticosteroids. They are indicated in large doses at the risk of respiratory distress syndrome in a newborn. In case of premature pregnancy, the maturation of the lungs is accelerated.
With persistent bleeding, which poses a threat to the pregnant woman, an emergency caesarean section is performed. Planned intervention is performed at a gestational age of 36-37 weeks, if the weight of the fetus exceeds 2500 g and there are signs of maturity of its lung tissue. The access and volume of the operation is determined by the location and depth of attachment of the placenta. The incision is performed corporally or in the lower uterine segment. With abundant incessant bleeding after the extraction of the child, uterotonic agents are injected, mattress or tightening sutures are applied to the uterine tissues. If there is no effect, the uterine, ovarian and internal iliac arteries are ligated. In extreme cases and with a true increment of the placenta, the uterus is extirpated. In the postoperative period, antibacterial agents are mandatory.
Prognosis and prevention
The prognosis depends on the timeliness of pathology detection and the validity of medical tactics. Maternal mortality rates of pregnant women with a fully present placenta are close to zero, however, such women usually have increased blood loss during surgery. The perinatal mortality rate reaches 10-25%, the main cause of death of children is their prematurity. Taking into account the established risk factors, for the purpose of primary prevention, timely treatment of infectious and inflammatory diseases of the female genital area, pregnancy planning with refusal of abortions, unjustified invasive procedures (diagnostic curettage, conservative myomectomy, etc.) is recommended. For the prevention of complications, early registration with an obstetrician-gynecologist and ultrasound in the recommended time is important.