The placenta accreta is defined as a placenta that is abnormally adherent to the myometrium. It can thus invade the entire thickness of the myometrium (placenta increta) or even exceed the serosa and invade neighboring organs (placenta percreta). It is a rare obstetric pathology with significant morbidity, and its management most often requires hemostatic hysterectomy. Its frequency has increased significantly in recent decades due to the increased rate of caesareans.

The maternity center of Tunis ( CMNT ) is a level 3 maternity center, supporting over 12 000 births yearly, where the caesarean section's rate is very high, close to 45% of deliveries. Recently we noted an increase in abnormal placental invasion incidence : in 2018, we report over 60 cases of placenta accreta,increta and percreta.

Early detection of these patients can help reduce potential risks. Ultrasound and MRI are the main diagnostic tools, but each one has weaknesses. Biological approch of this diagnosis is not well studied. Recently, BNP has been shown to be associated with increased angiogenesis. Because placenta accreta is characterized by abnormal uteroplacental neovascularization, it has been hypothesized that serum BNP levels may be related to abnormal invasion of the placenta.

In the literature, only one study investigated the relationship between cardiac biomarkers (Pro-BNP, CK, CK-MB and troponins) and abnormalities of placental adhesion. The main conclusion was that the Pro-BNP could predict placental accretisation.

Thus, the BNP as a mean of screening, could enrich our diagnostic arsenal. The purpose of our study is to determine whether or not BNP can predict abnormal placental invasion during pregnany.

The investigators will conduct a monocentric , prospective, observational study, including 60 pregnant women, with history of at least one previous uterine scar, and scheduled for cesarian delivery. The participants will be divided into 3 equal groups according to the imaging data obtained by a senior ultrasonographer , and the MRI data when necessary :

Ultrasonography will be performed in all participants. If placenta previa is diagnosed, without any suggestive signs of abnormal placental invasion, the patient is assigned to group P.

If placenta previa is diagnosed, and associated to suggestive signs of abnormal placental invasion,the patient is assigned to group I and an MRI will be performed.

If the ultrasonography is free of any suggestive signs of placenta previa, the patient is assigned to group N.

Finally :

• group P : pregnant women with placenta previa on ultrasound and no suggestive signs of abnormal placental invasion
• group I : pregnant women with placenta previa on ultrasound, and suggestive signs of abnormal placental invasion on ultrasound .
• group N : pregnant women without suggestive signs of placenta previa or abnormal placental invasion on ultrasound

After written and informed consent are obtained, a standard battery of blood tests including serum BNP will be runned.

For every patient, the following will be recorded : anthropometric measurements, previous obstetric and medical history, emergency or elective surgery, anesthetic technique, per-operative findings (placenta previa, placenta previa with abnormal placental invasion (accreta, increta, percreta), placenta normally located), amount of blood products transfused, nature of haemostasis procedures, complications.

Patients will be excluded, if their condition may cause a rise in serum BNP during the sample collection, those being: preterm premature rupture of membranes, acute anaemia or metrorrhagia, active labor, severe infections, arterial hypertension, known pulmonary hypertension, symptoms of heart failure, known hypertrophic or restrictive cardiomyopathy, history of valvular or congenital heart disease, atrial and ventricular tachyarrhythmias, pulmonary embolism, chronic obstructive pulmonary disease, kidney failure or renal dysfonction, liver dysfonction, severe metabolic and hormone abnormalities ( thyrotoxicosis or diabetic ketosis ), drug use possibly affecting cardiovascular system ( beta-blocker or other cardiovascular drug).

ANESTHETIC MANAGEMENT:

The timing of delivery is usually between 36 and 37 weeks for group P and I, and after 38 weeks for group N.

General anesthesia will be performed in pregnant women from group I and P. Regional anesthesia will be performed in pregnant women from group N.

Hemodynamic management during anesthesia for group I will require placement of 2 peripheral large-bore venous access, a desilet catheter in the femoral vein, and an arterial line preoperatively.

In patients from group P, 2 peripheral large-bore venous access will be placed preoperatively. A desilet catheter and arterial line will be obtained if necessary upon the anesthesiologist judgment.

In patients from group N, 1 peripheral large-bore venous access will be placed prior to the beginning of surgery.

Blood transfusion requirements will be based on the hemodynamic status, the amount of blood loss, the need of catecholamines and the anesthesiologist's experience.

Peroperatively, final diagnosis will be made according to surgical findings. If placenta is completely and easily removed, the diagnosis of abnormal placental invasion will not be retained.

If placenta could not be easily and completely removed, the diagnosis of abnormal placental invasion in established, and the case is carried out according to our surgical and anesthetic standards of management.

After collecting all groups, blood samples will be analysed for BNP, in a unique serie of tests.

Inclusion Criteria:

• pregnant women with suspected placenta accreta on ultrasound or MRI
• pregnant women with suspected placenta previa on ultrasound or MRI
• pregnant women without sugestive signs of placenta previa or accreta on ultrasound
• history of at least one previous uterine scar
• written and informed consent

Exclusion Criteria:

• Preterm premature rupture of membranes
• Acute anaemia or metrorrhagia
• Active labor
• Severe infections
• Arterial hypertension
• known Pulmonary hypertension
• Symptoms of heart failure
• Known hypertrophic or restrictive cardiomyopathy
• History of valvular or congenital heart disease
• Atrial and ventricular tachyarrhythmias
• Pulmonary embolism
• Chronic obstructive pulmonary disease
• kidney failure or renal dysfonction
• Liver dysfonction
• Severe metabolic and hormone abnormalities ( thyrotoxicosis or diabetic ketosis )
• drug use possibly affecting cardiovascular system ( beta-blocker or other cardiovascular drug)

60 parturients free from any exclusion criteria , devided equally into 3 groups :

• group P : parturients with placenta previa on ultrasound and no suggestive signs of placenta accreta
• group A : parturients with placenta previa on ultrasound, and suggestive signs of placenta accreta on ultrasound and / or MRI
• group C : parturients without suggestive signs of placenta previa or accreta on ultrasound