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A Phase III Study of Sildenafil to Reduce Adverse Perinatal Outcomes in Pregnant Women Carrying Small‑for‑Gestational‑Age Fetuses

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What is this trial about?

A plain-language summary of the goals, design and what participants do

The study focuses on pregnant individuals carrying a single baby that is classified as a small‑for‑gestational‑age fetus, meaning the baby's weight is below the 10th percentile for its gestational age. The investigation evaluates the use of sildenafil citrate, an oral medication, compared with a placebo given during labor.

The purpose of the study is to determine whether giving the medication during labor can lower the chance of serious problems for the baby around the time of birth. Participants are randomly assigned to receive either the medication or the placebo, and neither the participants nor the caregivers know which one is given. The treatment is taken in the labor setting and the mother and baby are observed through delivery and the first week after birth.

Outcomes being tracked include the need for assisted delivery methods such as forceps or vacuum (instrumental delivery), emergency caesarean section performed because of concerns for the baby, early death of the baby up to seven days after birth, breathing problems caused by meconium (a newborn's first stool) in the lungs, a low blood‑acid level (acidosis), a low score on the five‑minute Apgar test (a quick assessment of a newborn's health), and admission to a special care unit for newborns. These measures help researchers understand any benefit the medication may provide for babies who are smaller than expected at birth.

The research process

The trial runs in 9 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Randomization

    After joining the study, you will be randomly assigned to receive either sildenafil or a matching placebo. The study is double‑blind, so you will not know which one you receive.

  2. Step 2

    Baseline Assessment

    A health check will be performed, including confirmation that the fetus is small‑for‑gestational‑age (estimated weight below the 10th percentile).

    Standard laboratory tests and an ultrasound may be done to record your condition before labour begins.

  3. Step 3

    Preparation for Labour

    You will be placed under routine monitoring for labour, and the medical team will explain the procedures that will be followed during delivery.

  4. Step 4

    Administration of Study Medication

    When labour starts, you will take a single oral dose of 150 mg of sildenafil (or the identical placebo). The medication is provided as a film‑coated tablet.

    The dose is taken only once, during the active phase of labour.

  5. Step 5

    Monitoring During Labour

    Your vital signs and the baby's heart rate will be continuously monitored.

    Special ultrasound measurements may be performed to assess blood flow in the uterine artery, umbilical artery, and middle cerebral artery. These measurements are used to evaluate how the medication affects blood flow.

  6. Step 6

    Delivery

    The type of delivery will be recorded, including any instrumental delivery (use of forceps or vacuum), emergency caesarean section (surgical delivery performed because of fetal risk), or vaginal birth.

    Any occurrence of fetal or early neonatal death (up to 7 days after birth) will be noted.

  7. Step 7

    Immediate Newborn Assessment

    The newborn will be evaluated for a 5‑minute Apgar score (a quick test of health), signs of meconium aspiration (breathing in fetal stool), and blood‑gas results to check for neonatal acidosis (low pH).

    If needed, the baby will be admitted to the Neonatal Unit for further care.

  8. Step 8

    Post‑Delivery Monitoring

    You will remain under observation for conditions such as preeclampsia (high blood pressure), severe preeclampsia, eclampsia (seizures), and postpartum haemorrhage (excessive bleeding).

    Any serious adverse events will be recorded by the study team.

  9. Step 9

    Final Follow‑Up Visit

    Around 7 days after birth, a final visit will be scheduled to assess the newborn's weight, overall health, and any remaining morbidity.

    All study data will be collected and the trial participation will be concluded.

Who can join the trial?

8 criteria

  • You are an adult pregnant woman between 18 and 50 years old.
  • You are carrying a single baby (not twins) and the pregnancy is between 37 and 42 weeks long, which is the normal time range for full‑term pregnancy.
  • The baby is positioned head‑first, known as cephalic presentation.
  • You have had an early pregnancy ultrasound that measured the baby’s size from crown to rump, called crown‑rump length (CRL).
  • Your baby’s estimated weight is below the 10th percentile for its age, meaning it is classified as small‑for‑gestational‑age (smaller than most babies at the same stage).
  • You plan to have a vaginal birth, which means delivery through the birth canal (planned vaginal delivery).
  • You are being admitted when labor begins with the cervix less than 4 cm dilated, or you have a scheduled induction of labor (medical start of labor).
  • You can understand the study information and are able to give informed consent (agree voluntarily after being fully informed).

Who cannot join the trial?

16 criteria

  • Having a baby with chromosomal abnormalities, fetal infections, genetic changes, or major birth defects.
  • Taking the medication fosamprenavir at the same time as the study drug.
  • Taking strong or moderate medicines that block the enzyme CYP3A4 (examples: ketoconazole, itraconazole, ritonavir, saquinavir, erythromycin, cimetidine, darunavir) or the drug bosentan.
  • Taking medicines that block alpha‑adrenergic receptors (these are drugs that lower blood pressure).
  • Taking calcium channel blockers, especially verapamil (drugs that affect the heart and blood vessels).
  • Having leukaemia or multiple myeloma (types of blood cancers).
  • Being enrolled in another clinical trial that uses medicines.
  • Being unable to follow the study plan or attend the required follow‑up visits.
  • Having serious or unstable heart or blood‑vessel disease, such as recent unstable angina (unstable chest pain), acute myocardial infarction (heart attack), severe arrhythmias (irregular heartbeats), or a cerebrovascular accident (stroke).
  • Having low blood pressure (hypotension) or high blood pressure that is not under control (uncontrolled hypertension).
  • Having severe liver disease (severe hepatic impairment) or severe kidney disease (severe renal impairment).
  • Having a past history of a specific eye problem called non‑arteritic anterior ischemic optic neuropathy or a condition called retinitis pigmentosa.
  • Being allergic or overly sensitive to sildenafil or any of its inactive ingredients (excipients).
  • Having an active bleeding disorder, an active stomach ulcer (peptic ulcer), or any condition that makes bleeding more likely.
  • Taking nitrate medicines or other nitric oxide donors (such as nitroglycerin, glyceryl trinitrate, isosorbide dinitrate, mononitrate, sodium nitroprusside), or the drugs riociguat or nicorandil.
  • Taking other phosphodiesterase type 5 inhibitor medicines or having used sildenafil before, including its use for lung high blood pressure (Revatio®).
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Investigated drugs

Sildenafil is a medicine that widens blood vessels to improve blood flow. In this study, it is taken by mouth during labour by pregnant individuals whose babies are smaller than expected for their gestational age. The trial is testing whether giving sildenafil at this time can lower the risk of complications for both the baby and the mother around birth.

What is already known about the treatment

  • Sildenafil

    It is taken by mouth as a film‑coated tablet, usually 150 mg in this study, and is already approved and widely used for treating erectile dysfunction and pulmonary arterial hypertension; its use in pregnancy is still experimental and being studied in clinical trials. The drug works by blocking an enzyme called phosphodiesterase‑5, which raises levels of a chemical that relaxes blood vessels and improves blood flow. This action may help increase blood flow to the placenta during labour, aiming to lower the risk of problems for babies that are smaller than expected. Sildenafil belongs to the class of phosphodiesterase‑5 inhibitors.

  • Placebo

    The placebo is given as a tablet that looks like the active drug but contains no medicine, and it is taken by mouth in the same way as the sildenafil tablet; it serves only as a control in the trial and has no therapeutic effect. It is not a marketed medication and is used solely for research purposes. Because it contains no active ingredient, it does not act on any body system or have a pharmacological classification. The placebo helps researchers compare the true effect of sildenafil against a neutral baseline.

Investigated diseases

Small-for-gestational-age fetus - A condition in which the fetus’s estimated weight is below the 10th percentile for its gestational age, indicating slower growth than expected. The growth lag typically becomes more apparent in the third trimester as the fetus fails to keep pace with normal growth curves. This condition reflects limited supply of nutrients or oxygen from the placenta, which may persist or worsen as pregnancy continues. As the pregnancy approaches term, the fetus may remain small despite ongoing gestation. The reduced growth can affect fetal body composition and organ development. Monitoring focuses on the fetus’s size and blood‑flow patterns.
Trial detailsLast updated 18 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2026-526112-37-00Protocol codeFSJD-SILDEPAR-2026Estimated enrolment500 patientsSponsorFundacio Sant Joan De Deu

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