A Pilot Study: High Versus Low Oxytocin Dosing for Induction of Labor in Pregnant Patients With Obesity

The HILIO Trial: High vs. Low Oxytocin Dosing for Induction of Labor in Pregnant Patients With Obesity- PILOT STUDY

Pregnant patients with obesity are more likely to undergo induction of labor and have a higher risk of failed induction compared to patients with normal weight. The association between maternal obesity and labor dysfunction leading to cesarean delivery is poorly understood. Oxytocin is the mostly common medication used in induction of labor, yet optimal dosing of this medication is unknown. Studies have suggested that patients with obesity may be less responsive to oxytocin. This trial will compare a high and low dose oxytocin dosing regimen for the induction of labor in women with obesity.

This study is a pragmatic single center randomized, double blinded controlled trial. Nulliparous women with a pre-pregnancy body mass index (BMI) ≥30 kg/m2 undergoing induction of labor at ≥37 weeks' gestation will be eligible for enrollment. Women will be randomly allocated to receive oxytocin using either a high-dose or low-dose regimen. Patients, providers, and research staff will be blinded to the dosing regimen. All other aspects of obstetric management will be at the discretion of the patient's clinical care team.

Postpartum maternal, neonatal, and delivery outcomes will be collected. Postpartum data through hospital discharge will be collected from the medical record. Information about complications following hospital discharge through 6 weeks after delivery will be collected during a research follow-up telephone call performed 6-8 weeks following delivery.

Inclusion Criteria:

1. Nulliparity
2. Maternal age >18 years
3. Gestational age ≥37w0d
4. Induction of labor, defined as initiation of labor with medication or intracervical Foley catheter in a patient without observed spontaneous cervical change and <6 contractions per hour (average of one contraction every 10 minutes) at the time of initial presentation. Women with prelabor rupture of membranes (PROM) can be included if the other criteria are also met with regards to cervical dilation and contractions.
5. Singleton gestation
6. Cephalic presentation
7. Indication for oxytocin use in the first stage of labor
8. No contraindication to labor or vaginal delivery
9. Pre-pregnancy BMI ≥30 kg/m2 based on patient report and confirmed by pre-pregnancy or first trimester weight as recorded in the medical record
10. Cervical dilation ≤4 cm at time of initiation of induction

Exclusion Criteria:

1. Fetal demise
2. Major fetal congenital malformation or known chromosomal abnormality
3. Prior uterine surgery (e.g., cesarean, myomectomy)
4. Non-reassuring fetal wellbeing as indication for induction
5. Intraamniotic infection suspected or diagnosed prior to randomization
6. Non-English
7. Multifetal gestation
8. Gestational age <37 weeks
9. Spontaneous labor
10. Cervical dilation > 4 cm at initiation of induction
11. Initiation of oxytocin in the second stage of labor
12. Use of oxytocin prior to randomization or planned use of oxytocin with foley catheter for cervical ripening
13. Fetal malpresentation
14. Estimated fetal weight >4500 g in a patient with diabetes, or estimated fetal weight >5000 g in a non-diabetic patient
15. Abnormal placentation (e.g. previa, suspected placenta accreta spectrum)
16. Physician/provider or patient refusal