The rate of caesarians dramatically increased for 15 years. The main indication of caesarian became the iterative caesarian of principle because of a history of caesarian. Any attempt of reduction of the rate of caesarians should thus focus on the indications of iterative principal caesarean. Nevertheless, the main reason usually evoked to justify a reduction of the attempts of low way after caesarian is the concern generated by the risk of uterine break during the trial of labor. Yet, there is no reliable method to predict this risk of uterine break. A way of interesting research consists in estimating the potential profits of the echography of the scar lower segment. Indeed, the echography can be useful to determine the specific risk of uterine break of a patient by measuring the thickness of the lower segment of the womb.

The strong negative predictive value of the echography of the lower segment on the risk of uterine break should encourage the women encircled to accept a trial of labor. That is why, this examination associated with a rule of decision could help to decrease the rate of iterative elective caesarians and especially to decrease the mortality and the foetal and maternal morbidity connected to the trial of labor among the patients having a history of caesarian.

"Lower Uterine Segment Trial (LUSTrial)" Evaluation of the efficiency of the ultrasound measure of the thickness of the lower segment associated with a rule of decision to reduce the foetal and maternal morbidity and mortality in the coverage of the deliveries of the women having a history of caesarian: a pragmatic randomized trial

Aim Evaluation of the efficiency of the ultrasound measure of the thickness of the lower segment associated with a rule of decision to reduce the foetal and maternal morbidity and mortality in the coverage of the deliveries of the women having a history of caesarian Methodology Randomized trial, multicentric, open, in two parallel arms.

Evaluated treatments:

Between 36+0 and 38+6 weeks of amenorrhea, the patients will be invited to participate in the study. After agreement, the patients respecting the criteria of inclusion and not inclusion will be randomized in two groups:

GROUP A (experimental group) : The ultra sound measure of the thickness of the lower segment will be realized in a way standardized by expert sonographers. The patient will be informed that in case of measure:

• superior at the threshold of 3.5 mm, her will be considered " a low risk " by complications and will be encouraged to try a event of the work
• subordinate or equal at the threshold of 3.5 mm, her will be considered " at risk " by complications and will be encouraged to give birth by iterative elective caesarian.

GROUP B (control group) : The ultra sound measure of the lower segment will not be realized. The mode of delivery will be decided according to the current clinical practice.

Inclusion Criteria:

• age ≥ 18 years
• unique pregnancy
• gestational age between 36 SA and 38SA +6 days
• cephalic presentation
• lower uterine segment section's history
• sign consent

Exclusion Criteria:

• age < 18 years
• history of longitudinal incision's caesarean
• iterative caesarean indication
• multiple pregnancy
• placenta praevia
• patient refuse trial of labor
• absent consent