Study Design and Approval
This was a randomised controlled trial - a scientific study designed to compare two groups as fairly as possible. It took place in four hospitals in Belgium:
Ziekenhuis Oost-Limburg (ZOL), Genk
AZ Sint-Lucas, Brugge
Jessa Ziekenhuis, Hasselt
University Hospital Antwerp (UZA), Antwerp
The study ran from May 2017 to November 2023. It was carefully reviewed and approved by the Ethics Committee of ZOL Genk and the review boards of the other hospitals to make sure it followed strict ethical and safety standards.
Who Could Take Part?
Women were eligible to join the study if they:
Were over 18 years old
Were pregnant with just one baby
Had a baby in the head-down (cephalic) position
Had a Bishop Score of 6 or less (indicating the cervix wasn't ready for labor)
Needed their labor to be induced for low-risk reasons, such as:
Being past their due date (post-term)
Suspected large baby (macrosomia)
Personal request to induce labor after 38 weeks of pregnancy
Women were not allowed to join the study if they had any of the following:
Twins or more (multiple pregnancy)
Preterm premature rupture of membranes (water breaking too early)
A baby not growing well (fetal growth restriction)
A condition called placenta accreta spectrum (PAS)
A previous cesarean section
Baby not in head-down position
Gestational diabetes or high blood pressure during pregnancy
Lived more than 60 minutes away from the hospital
Any other health issues (maternal or fetal) or reason that made vaginal birth unsafe
How Were Women Assigned to Groups? Women were told about the study by their doctor in the days leading up to labor induction. On the day of induction, a hospital doctor checked if they met the criteria. If they did, the woman was asked to sign a consent form to take part in the study.
Once enrolled, each woman was randomly assigned to one of two groups:
Inpatient group - stayed in the hospital after balloon insertion
Outpatient group - went home after balloon insertion
The randomisation was done using a computer program, so neither the doctors nor patients could influence which group they were placed into. Because it was obvious who went home and who stayed, this study was not blinded.
The Induction Procedure All four hospitals had experience using mechanical methods to start labor. Before the study began, all staff received a brief training guide to ensure the procedure was done the same way in every hospital.
How the Balloon Was Inserted:
A double-balloon catheter (Cook balloon) was gently inserted into the cervix using a special tool under direct view with a vaginal speculum.
The lower balloon (inside the uterus) was first filled with 20 ml of saline.
The balloon was pulled back so that it rested properly in the cervix.
Then both balloons (one inside the uterus and one in the vagina) were gradually filled with saline up to 80 ml each.
The catheter was taped to the woman's thigh to keep it in place, but no tension or pulling was applied.
After insertion, each woman was monitored for 2 hours using CTG to check the baby's heart rate and any contractions.
If the CTG after balloon insertion was not normal (e.g., slow heartbeat, signs of stress), the woman stayed in the hospital, even if she was in the outpatient group.
Outpatient Group: Going Home If the CTG was normal, women in the outpatient group went home with the balloon still in place and were asked to return to the hospital 12 hours later, unless one of the following happened: their water broke (spontaneous rupture of membranes), they started having strong or painful contractions, the balloon came out or moved, they experienced non-tolerable pain or felt anxious, they simply didn't want to go home.
Before going home, every woman was given clear, written instructions about: when to come back early, what warning signs to look for, how to call the hospital, they also received a follow-up call from the doctor on duty 1-2 hours after leaving, to check how they were doing.
After 12 Hours: Balloon Removal and Next Steps. Twelve hours after the balloon was placed (or sooner, if needed), the balloon was removed. At that time the Bishop Score was checked again to see if the cervix had softened or opened. A new CTG was performed to make sure the baby was doing well.
What happened next depended on how the cervix looked: if the cervix was still not ready (Bishop Score ≤ 6):
→ Labor was continued using prostaglandins (a medication to soften the cervix)
If the cervix was ready (Bishop Score \> 6) and effaced (thinned out):
→ Labor was started by breaking the water (amniotomy) and giving oxytocin to strengthen contractions
If the cervix was open but not thinned, doctors often chose oral or vaginal prostaglandins instead of breaking the water.
All clinical details were recorded by trained hospital staff.
Primary Outcome (Main Focus):
The baby's wellbeing as seen on the CTG (heart rate monitor) right after the balloon was inserted and again when it was removed (or sooner if problems occurred).
Secondary Outcomes (Other Important Measures):
1. Maternal Clinical Outcomes:
How the baby was delivered (normal, assisted with vacuum or forceps, cesarean)
Pain relief used (e.g., paracetamol, pethidine, epidural)
Use of labor medications like oxytocin
2. Process Outcomes:
How long the entire induction process took:
From hospital admission to discharge
From balloon placement to delivery
From balloon removal to delivery
3. Maternal Satisfaction:
Assessed using a detailed 16-question survey sent by email 1-2 days after delivery
Topics included overall experience, comfort, timing, and whether they'd choose the same method again
4. Maternal Health Concerns:
Possible complications like:
Uterine hyperstimulation (too many contractions)
Placental abruption (placenta detaching early)
Infections needing antibiotics
Doctors also recorded why some women needed C-sections or assisted births.
