Cook´s Balloon Versus Dinoprostone for Labor Induction of Term Pregnancies With Fetal Growth Restriction

Late-onset fetal growth restriction (FGR) represents the most common subtype of FGR (70-80%). The greatest risk for these fetuses appears once term pregnancy is reached, when stressful situations are added to their status of relative hypoxia, such as the appearance of contractions and funicular compression. Thus, it has been shown that from week 37-38 the risk of intrauterine mortality increases and there is a general consensus not to prolong these pregnancies beyond this period. In this situation, induction of labor is usually preferred over elective caesarean delivery. However, these fetuses have an increased risk of cesarean section for suspected fetal distress.

Mechanical methods for cervical ripening are associated with less uterine stimulation with a lower rate of tachysystole than prostaglandins. Therefore, these methods have been proposed as the optimal approach for late-onset FGR, since they could reduce the rate of cesarean sections for suspected fetal distress. However, there is no published randomized controlled trials on the use of different methods of cervical ripening for labor induction in late-onset FGR.

Thus, the investigators postulate that, in late-onset FGR, cervical ripening with a mechanical method (Cook´s balloon) achieves a higher percentage of vaginal deliveries than a pharmacological method (vaginal dinoprostone), being safe for both the mother and the newborn.

The main aim of this study is to evaluate whether cervical ripening with Cook balloon for labor induction at term gestation of singleton pregnancies with late-onset FGR achieves a higher rate of vaginal delivery compared to the use of vaginal dinoprostone. Neonatal safety outcomes (neonatal acidosis, the MAIN morbidity score, and NICU admission) will be analyzed as secondary endpoints, in a descriptive manner.

Inclusion criteria

• Singleton pregnancy
• Age ≥ 18 years
• Gestational age (GA) dated by first trimester ultrasound ≥ 37+0 weeks
• Cephalic presentation
• Stage I fetal growth restriction, defined as the presence of at least one of these two criteria:

• Estimated fetal weight (EFW) < 3rd percentile
• EFW < 10th percentile and at least one of the following: 2.1) Umbilical artery pulsatility index > 95th percentile or 2.2) Cerebral-placental index < 5th percentile
• Bishop score < 7
• Intact fetal membranes
• No previous caesarean section
• No contraindications for vaginal delivery or labor induction.

Exclusion criteria

• Major fetal malformation
• Fetal genetic abnormality
• Fetal congenital infection