Effect of Increased Oxytocin Doses on the Mode of Delivery in Obese Primiparous Women With Spontaneous or Induced Labour (PROXYMA)

Effect of Increased Oxytocin Doses on the Mode of Delivery in Obese Primiparous Women With Spontaneous or Induced Labour. A Double-blind, Randomised, Controlled Trial

The rate of caesarean section is higher among obese pregnant women, leading to increased morbidity in this already vulnerable population. Oxytocin is the main drug used in obstetrics to optimize progress of labour, but observational studies have suggested that its efficiency may be insufficient in obese women with usual doses.

We design a randomised controlled trial to test the effect of an increased oxytocin dose on the rate of caesarean section in obese primiparous women with spontaneous or induced labour.

Study Overview

• Status: Completed
• Conditions: Obese; Oxytocin; Primiparous Women
• Intervention / Treatment: Drug: Oxytocin 4 mIU/mL; Drug: Oxytocin 2 mIU/mL

Detailed Description

The hypothesis underlying this trial is that an increase in oxytocin dose can reduce the rate of caesarean sections in primiparous obese patients, with a spontaneous or induced onset of labour, without increasing maternal or neonatal morbidity. This would be a major step forward in reducing morbidity in an at-risk population and in improving the obstetric prognosis for future pregnancies.

The research is a double-blind controlled trial, including primiparous obese women in spontaneous or induced labour, for whom a prescription of oxytocin is decided. Oxytocin is currently indicated for notably "insufficiency of uterine contractions, at the beginning or during labour".The recommended dosage in the market authorization will be used for the control group.

The control group will receive oxytocin at 2 milli-International unit /mL and the intervention group at 4 milli-International unit /mL, controlled by pump (final volume = 500 mL) or electrical syringe (final volume = 50 mL).

The primary objective is to compare the effect of higher doses of oxytocin (intervention group) vs standard doses of oxytocin (control group) on the rate of caesarean sections in obese patients with spontaneous or induced onset of labour.

The secondary objectives will be to compare the effect of higher doses of oxytocin (intervention group) vs standard doses of oxytocin (control group) on maternal and labour complications (length of labour, arrest of labour, interruption of oxytocin perfusion and reason, uterine hyper-stimulation, mode of vaginal delivery, reason for caesarean section, post-partum haemorrhage, maternal blood transfusion, volume of oxytocin infusion, oxytocin side effects), as well as foetal complications and neonatal complications.

• Study Type: Interventional
• Enrollment (Actual): 443
• Phase: Phase 4

Contacts and Locations

Study Locations

• France
  • Angers, France
    • CHU d'Angers
  • Bordeaux, France
    • CHU de Bordeaux (Pellegrin)
  • Clamart, France
    • Hôpital Béclère
  • Le Kremlin-Bicêtre, France, 94270
    • Hôpital Bicêtre
  • Montpellier, France
    • CHU de Montpellier
  • Nîmes, France
    • CHU de Nîmes
  • Paris, France
    • Hopital Tenon
  • Paris, France
    • Hôpital Cochin Port Royal
  • Poissy, France
    • CHU de Poissy St Germain
  • Saint-Etienne, France
    • CHU de Saint Etienne
  • Schiltigheim, France
    • CHU de Strasbourg (Centre Médico Chirurgical et Obstétrical)
  • Strasbourg, France
    • CHU de Strasbourg (Hôpital de Hautepierre)

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years and older (Adult, Older Adult)
• Accepts Healthy Volunteers: No

Description

Inclusion criteria

Inclusion criteria are the following:

• Age ≥ 18 years
• Nulliparous (no previous childbirth beyond 22 SA)
• BMI ≥ 30 kg/m² at the beginning of pregnancy
• Singleton pregnancy
• Spontaneous or induced onset of labour
• Cephalic presentation
• Term ≥ 37 weeks of gestation and < 42 weeks of gestation
• Medical Indication and absence of medical contraindication for oxytocin during labour: inadequate and/or ineffective uterine contraction and/or delayed cervical dilation
• Written consent
• Affiliation to a french social security system

Exclusion criteria

Exclusion criteria are the following:

• Hypersensitivity to the active substance (oxytocin), to any of its excipients or to latex (risk of cross allergy)
• Medical contraindication for oxytocin
• Coagulation disorders
• Foetal growth restriction (inferior to 5th percentile)
• Foetal malformation (major)
• Foetal heart rate anomalies before use of oxytocin (at the time of inclusion)
• History of uterine surgery (scarred uterus of gynaecological origin)
• Patient with a disease requiring caesarean section prior to labour (planned caesarean section before labour)
• Severe renal failure
• Patient deprived of their liberty (under curatorship or guardianship)
• Participation in another interventional trial of category 1. Patients included in interventional research with minimal risk and constraints may participate in the study after the investigator's assessment.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Quadruple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Experimental group; The experimental group will receive oxytocin at 4 mIU/mL	Drug: Oxytocin 4 mIU/mL; Oxytocin at 4 mIU/mL administrated by IV infusion controlled by pump or electric syringe.
Active Comparator: Control group; The control group will receive oxytocin at 2 mIU/mL	Drug: Oxytocin 2 mIU/mL; Oxytocin at 2 mIU/mL administrated by IV infusion controlled by pump or electric syringe.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Rate of caesarean section during labour	The decision of caesarean section is made by the responsible obstetrician in charge of the patient, he or she will be blinded of the patient's group (oxytocin dosage) to avoid differential indication for caesarean section. Therefore, the decision to perform (or not) a caesarean section will be only based on foetal/maternal criteria, independently of oxytocin dosage.	through study completion, an average of 1 month

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Interruption of oxytocin perfusion and causes	Interruption of oxytocin perfusion (yes/no) and causes (foetal heart anomalies / uterine hyperkinesia / uterine hypertonia / other)	through study completion, an average of 1 month
Reason for the caesarean section	foetal heart anomalies / labour arrest / other	through study completion, an average of 1 month
Length of labour phases	Length of labour phases is measured in minutes (from 2 cm of dilation until delivery)	Through study completion, an average of 1 month
Arrest of labour	It will be evaluated if there is two or more hours without cervical dilation (yes/no)	Through study completion, an average of 1 month
Uterine hyper-stimulation	Uterine hyper-stimulation (more than 5 uterine contractions per 10 min)	Through study completion, an average of 1 month
Mode of vaginal delivery	Spontaneous or operative delivery.If operative vaginal delivery: indication	Through study completion, an average of 1 month
Post-partum haemorrhage	Post-partum haemorrhage (yes/no) and its volume (mL). Post-partum haemorrhage is defined as blood lost ≥ 500 mL in the 2 hours after birth.	Through study completion, an average of 1 month
Maternal blood transfusion	Maternal blood transfusion (yes/no) (for the duration of the hospitalization)	Through study completion, an average of 1 month
Volume of oxytocin infusion	Volume of oxytocin infusion (mL/H)	Through study completion, an average of 1 month
Oxytocin side effects	nausea, vomiting, headaches, increased or decreased heart rate, allergic reaction, skin rash	Through study completion, an average of 1 month
Foetal complications	Foetal heart rate anomalies requiring second-line monitoring (as pH/lactate blood test at scalp) or emergency delivery (yes / no); Appearance of meconium (yes / no); Chorioamnionitis (yes/no): defined as the combination of 2 of the next 3 signs: maternal fever more than 38°5 during labour and/or foetal heart tachycardia and/or biological infection sign	Through study completion, an average of 1 month
Neonatal complications	Apgar score at 5 min; Umbilical arterial cord pH; Neonatal resuscitation (yes / no): defined by at least artificial ventilation; Transfer to neonatal care unit (yes / no)	Through study completion, an average of 1 month

Collaborators and Investigators

• Sponsor: Assistance Publique - Hôpitaux de Paris
• Investigators: Principal Investigator: Alexandra BENACHI, PHD, MD, Antoine Béclère Hospital, APHP

Study record dates

Study Major Dates

• Study Start (Actual): October 2, 2021
• Primary Completion (Actual): December 30, 2024
• Study Completion (Actual): January 30, 2025

Study Registration Dates

• First Submitted: January 29, 2021
• First Submitted That Met QC Criteria: February 17, 2021
• First Posted (Actual): February 18, 2021

Study Record Updates

• Last Update Posted (Actual): December 26, 2025
• Last Update Submitted That Met QC Criteria: December 19, 2025
• Last Verified: August 1, 2025

More Information

Terms related to this study

• Keywords: Oxytocin; Obese; Primiparous women
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Overweight; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Obesity; Physiological Effects of Drugs; Reproductive Control Agents; Oxytocics; Oxytocin
• Other Study ID Numbers: 2020-002640-23

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No