The objective of the study ist to compare the Dilapan-S and the Cook Ballon device for the mechanical induction of labour in women with a previous C-section. There is currently lack of data regarding this comparison of the two methods for mechanical labour induction in this patient collective. Any method used for labour induction is therefore off-label. The primary outcome is the time between placement of the device and delivery. Ad secondary outcomes are among others the cesarean delivery rate and patient satisfaction with the induction method.

The cesarean section (CS) rate is increasing worldwide, with previous CS being an important factor contributing to this trend. The investigators think that VBAC may be safe, provided a careful selection of the patients is performed. The individual birth management is particularly important if labour has to be induced, as in case of approximately 25% of women attempting VBAC. Counselling patients about labour induction can be challenging, as they should be offered not only a safe, but also an effective method. Labor induction can be achieved by using several approaches: administration of drugs, which induce uterine contractions, such as prostaglandins or oxytocin, performing an amniotomy, or using mechanical methods. In Switzerland and implicitly in the investigators' institution, PGE after CS are rarely employed in carefully selected cases. Oxytocin administration after performing amniotomy is considered to be a safe method, but may be less effective with an unfavorable BISHOP score (<6).

An possible alternative in case of unripe cervix is induction of labour by use of mechanical methods: balloon catheters and laminaria stents. The investigators currently use the double balloon catheter device (Cook Inc) for this purpose. This device is inserted transcervically and both ballons are inflated with sterile 0.9% saline solution. The catheter remains in place until spontaneously expelled or until start of active labour. If neither happens, it will be removed after 12 hours, followed by oxytocin administration and amniotomy.

Recently, an alternative method for mechanical induction is gaining increased attention: the use of hygroscopic cervical dilators. The method seems to be equally effective and safe as directly compared to a single device catheter in a low risk population of women without uterine scar. When used in patients with previous cesarean section, the rate of spontaneous labour seems to resemble existent data for induction with balloon catheter, this including the investigators' collective.

One of the advantages of Dilapan-S® could be the lack of vaginal protrusion and the fact that it does not have to be fixated under tension. Women seem to feel more mobile with Dilapan®, the perception of relaxation moments between contractions as well as sleep periods during the induction seem to be improved with Dilapan®.

Inclusion Criteria:

• All women >= 18years old with a previous CS and an indication of labour induction, between 24-42 weeks of pregnancy.
• Modified Bishop-Score < 6
• Informed consent

Exclusion criteria:

• More than 1 CS
• Premature rupture of membranes
• Vaginal infection
• Intrauterine fetal demise
• Twin pregnancy
• Contraindication against labour induction or vaginal delivery
• Vaginal bleeding
• Simultaneous external administration of prostaglandins planned
• Placenta praevia, vasa praevia or placenta accreta spectrum
• Transverse fetal orientation
• Prolapsed umbilical cord
• Prior hysterotomy, classic uterine incision, myomectomy or any other full thickness uterine incision (except C-section)
• Pelvic structural anomaly
• Active genital herpes infection
• Invasive cervical cancer
• Abnormal fetal heart rate pattern
• Breech presentation
• Maternal heart disease
• Polyhydramnios
• Presentic part above the pelvic inlet
• Severe maternal hypertension

due to nature of the induction method, blinding of women an/ or doctors is considered non-feasible