Ridstress2 - Improving outcomes for women and small babies.

Fetal distress in labour

RidStress2 is a multicentre randomised controlled trial aiming to improve outcomes for women and small babies.  In Australia, almost 1 in 4 caesarean sections are performed for suspected fetal distress, which occurs when the placenta is unable to supply sufficient oxygen and nutrients in labour.  The only therapeutic options are emergency caesarean section or instrumental vaginal birth – both of which can have serious consequences.  Sildenafil Citrate (SC) dilates blood vessels, thus improving blood flow to baby.  RidStress2 evaluates the potential of SC to improve outcomes for women and small babies by reducing fetal distress during labour. 

A preliminary trial of 300 women at Mater Mothers Hospital published as a Report of Major Impact in the American Journal of Obstetrics and Gynaecology found that taking SC during labour reduced the need for caesarean section or instrumental birth by 50%. 

Trial Status
Trial Phase
Phase 3 Drug Trial
Trial contact details
Contact Person
Ridstress2 Team
What you need to know

Who can take part?

  • Women with a small for gestational age baby, planning a vaginal birth from 37 weeks gestation in hospital
  • Singleton or DCDA twin pregnancy
  • Women 18 years and older
  • Women willing and able to comply with study requirements


  • Women who have had 2 or more caesareans
  • Women who have had a classical caesarean
  • Women with severe kidney or liver dysfunction
  • Triplet or higher order multiple births
  • Contraindication to SC
  • Women who are taking nitrate drug therapy or are planning to utilise short-acting nitrate-containg in medication in labour (this is very rare)

What is involved for you?

The process for women who choose to participate in iSEARCH is as follows:

  • Read and sign a consent form, along with discussion with a Research Midwife or Doctor
  • Receive a blood test antenatally (we try to coincide this with other pathology)
  • When women present in established labour or if being induced, when waters are broken:
    • women receive a tablet in labour every 8 hours, with a maximum of 3 tablets
      • Half the women receive SC
      • Half the women receive a placebo
  • Once baby is born some blood is collected from the umbilical cord (this doesn’t hurt baby or mother)
  • The placenta will be sent for testing

Women will be contacted for a brief phone interview at one month, then every 6 months for 3 years.  The phone call at 2 years will take around 20 minutes, and includes a questionnaire regarding the child’s developmental milestones.

Trial dates

This trial is accepting participants until December 2024.

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