I. Incidence increases with the number of cesarean deliveries
The incidence of placenta praevia and placental implantation increases with the increase of uterine incision scar formation and endometrial damage. For those who had previous cesarean delivery with anterior placenta previa or central placenta previa, the incidence of abnormal placental position in the current pregnancy is twice as high as that of posterior placenta previa in the previous pregnancy. Pregnant women with a history of cesarean delivery are 35 times more likely to have placental implantation than those without a history of cesarean delivery.
II. Improving the rate of prenatal diagnosis of fatal placenta praevia
(I) Molecular biology techniques
1. Maternal serum alpha-fetoprotein (AFP) test
Placental implantation causes AFP in fetal blood to enter maternal blood directly, so its serum AFP level can be significantly increased, which can reach 2-5 times of normal control group. If the serum AFP of pregnant women is elevated, placental implantation should be considered after excluding fetal malformation and intra-placental hemorrhage.
2.Serum creatine creatinase (CK) test in pregnant women
The elevation of CK in placental implantation may be related to the invasion of trophoblast cells into the myometrium and destruction of myocytes, thus releasing CK into maternal blood.
3. Maternal serum free fetal DNA test
Because the maternal-fetal barrier is damaged during placental implantation, fetal cells leak into the mother through the damaged maternal-fetal barrier, therefore, detection of fetal DNA in maternal blood can help diagnose placental implantation.
(ii) Imaging tests
1. Color multispectral ultrasound examination of placenta praevia and placental implantation imaging criteria
Considering the fact that aggressive placenta praevia has a high rate of placental implantation, it is important to know whether the placenta is implanted or not to determine the degree of aggressiveness, as shown by the following placental imaging manifestations of placenta praevia.
(1) extensive intraplacental parenchymal flow.
(2) focal intraparenchymal placental hemorrhage.
(3) Excessive vascularity at the bladder-uterine plasma membrane interface.
(4) marked venous plexus visible at the base of the placenta.
(5) disappearance of the posterior placental space.
2.Gray scale examination
Gray-scale flow imaging technique has a high resolution of blood vessels, blood flow and its surrounding soft tissues. Placental implantation is manifested by.
(1) thinning and disappearance of the posterior placental hypoechoic area
(2) “Swiss cheese”-like echogenic dark areas and anechoic areas within the placenta
(3) The distance between the bladder wall and the plasma layer of the uterus becomes smaller
(4) Localized protrusion of the inner surface of the bladder
3.Magnetic resonance imaging (MRI) examination
MRI has a high tissue resolution, is sensitive to blood flow, and can clearly visualize the placenta. MRI can also clearly show the relationship between the uterus and the placenta. 88% sensitivity and 100% specificity for the diagnosis of placental implantation with MRI in pregnant women with a history of cesarean delivery who also have anterior wall placenta previa. For cases with ultrasound suspicion of placental implantation, MRI can finally make a clear diagnosis in most cases.
III. Treatment
(I) Points to note in prenatal examination
When performing color multispectral ultrasonography in pregnant women who are pregnant again after cesarean section, special attention should be paid to the location of placental attachment. If the placenta is attached to the lower part of the anterior wall of the uterus, clinical attention should be paid to it and regular follow up.
(II) Principles of treatment in different gestational weeks
1. Early pregnancy at the cesarean section scar
Before abortion, accurate diagnosis should be made, and if pregnancy at the cesarean scar is suspected, scraping is prohibited, and sufficient amount of MTX 100mg and RU-486250mg can be given in several times; if there is a lot of bleeding during abortion, the operation should be stopped immediately, and cervical pressure can be applied to stop bleeding, uterine artery embolization is also feasible, and if necessary, the uterus can be removed.
2.Mid-term pregnancy with aggressive placenta praevia
It is not possible to induce labor by conventional methods, because conventional methods cause contractions first, then exclude the embryo and placenta, and such patients may have uterine rupture and uncontrollable hemorrhage after initiating contractions. If there is no requirement for childbirth, drug chemotherapy such as MTX and RU-486, arterial embolization, cesarean section and hysterectomy can be used. If there is a requirement for childbirth, then conservative treatment with drug chemotherapy, arterial embolization and removal of pregnancy material will be used.
3.Late pregnancy, aggressive placenta praevia
It is more difficult to deal with, especially to emphasize the prenatal diagnosis, to make preparations before surgery, remember to be blind and unprepared.
Perioperative management
(1) The best time, timing, location and personnel should be chosen for the operation.
(2) Arrange experienced obstetricians on the stage.
(3) Experienced obstetricians should be present to organize resuscitation immediately if necessary.
(4) Anesthesiologist, and anesthesia method: choose the anesthesia method that guarantees the removal of the uterus at any time.
(5) The possibility of resuscitation of a born premature baby or a newborn is high, and a neonatologist should be present.
(6) Strengthen the detection of vital signs during and after surgery.
(7) To operate in a hospital with good medical rescue equipment.
(8) Establish unobstructed intravenous access.
(9) Prepare a suitable blood source.
(10) Pre-operative talk: the pregnant woman and her family should be informed of the risks of surgery and the possibility of simultaneous hysterectomy.
V. Points of attention for surgery
(1) The relationship between the placenta and the incision should be understood in detail through imaging data before surgery.
(2) Skilled cooperation of the main surgeon and assistant.
(3) The uterine incision should be chosen to avoid the placenta as far as possible, or if it cannot be avoided, the placenta should be cut from the lower part of the uterus (or at the edge), and the placenta should be pushed away quickly to break the membrane and deliver the fetus.
(4) Pay attention to the placental residue or placental implantation when detaching the placenta, partial implantation is feasible after wedge-shaped resection and re-suturing the muscle layer.
(5) If there is active bleeding on the abruptive surface of the placenta, the wound should be closed with absorbable suture “8” to stop bleeding, but of course, the suture should not be too tight.
(6) If the bleeding from the placental adhesion surface can be controlled, it is recommended to close the uterus quickly to maintain the continuity and integrity of the uterus.
(7) If there is still bleeding after ligation of the superior branch of the uterine artery, postpartum hemorrhage treatment such as filling the uterine cavity with gauze is used.
(8) If the bleeding does not stop even after the above treatment or if the placenta implants in a large area, hysterectomy should be performed decisively.