The aim of this study is to investigate if tocolysis with atosiban in late preterm birth (30 to 34 weeks) is (cost-) effective compared with placebo in improving neonatal morbidity and mortality.

Research question Does tocolysis with atosiban reduce neonatal mortality and mortality in women with threatened preterm birth between 30 and 34 weeks when compared to placebo?

Study design Multicenter, double blinded, placebo controlled RCT

Study population Women with threatened preterm birth between 30 and 34 weeks of gestation are eligible for the trial. More than 20 hospitals (including all 10 perinatal centres) in the Netherlands will participate in this trial, as well as 15 hospitals in the UK and 1 in Dublin, Ireland.

Threatened preterm birth is defined as listed below in the inclusion criteria. Our previous APOSTEL III study showed that half of the women with these criteria deliver within seven days, validating this definition of women at high risk for preterm birth.

Inclusion criteria

• Women ≥ 18 years old

• Singleton or twin pregnancy

• Gestational age between 30 0/7 and 33 6/7 weeks

• Threatened preterm birth defined by regular uterine contractions, AND one of the following:

  • Cervical length of < 15 mm OR
  • Cervical length of 15-30 mm and a positive Fibronectine test (≥ 50 ng/mL) OR
  • In case of absence of cervical length measurement in local protocol a positive Fibronectin test or Partus test OR
  • Ruptured amniotic membranes

Exclusion criteria

• Previous treatment for threatened preterm birth with corticosteroids.
• Contra-indication for tocolysis
• Signs of fetal distress
• Signs of intra uterine infection

Participants RCT: 760 (380 per group)

Description of intervention(s) Tocolysis with atosiban versus placebo.

Outcome measures The primary outcome is a combined perinatal outcome of severe neonatal morbidity and perinatal mortality Secondary outcomes will be birth within 48 hours, time to delivery, gestational age at delivery, birth weight, number of days on invasive mechanical ventilation, length of admission in NICU, convulsions, asphyxia, meningitis, pneumothorax and mortality until 3 months corrected age, maternal infection, maternal side effects and costs.

All outcomes are in the electronic patient file. No additional tests are required for mother or baby.

Power / data analysis Based on the APOSTEL 3 data, the proportion of adverse perinatal outcome in women randomized between 30 and 34 weeks gestation and treated with atosiban was 6%. Based on two recent studies, we expect a 49,8% reduction of 11,95% adverse perinatal outcome in the placebo group to 6% in the atosiban group. Therefore we need to randomize 722 women (beta-error 0.2; alpha error 0.05). Assuming a 5% drop-out rate, we need to randomize 760 women (380 in each arm).

Inclusion Criteria:

• Women ≥ 18 years

• Singleton or twin pregnancy

• Gestational age between 30 0/7 and 33 6/7 weeks

• Threatened preterm birth defined by regular uterine contractions, AND one of the following:

  • Cervical length of < 15 mm OR
  • Cervical length of 15-30 mm and a positive Fibronectine test (≥ 50 ng/mL) OR
  • In case of absence of cervical length measurement in local protocol a positive Fibronectin test or Partus test OR
  • Ruptured amniotic membranes

Exclusion Criteria:

• Previous treatment for threatened preterm birth with corticosteroids in current pregnancy
• Contra indication for tocolysis
• Signs of fetal distress
• Signs of intra uterine infection

Double blinded