Maternal sildenafil for severe fetal growth restriction (STRIDER): a multicentre, randomised, placebo-controlled, double-blind trial
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In this randomized, double-blind, placebo-controlled trial, sildenafil (25 mg three times daily) failed to prolong pregnancy or improve perinatal outcomes in women with severe early-onset fetal growth restriction.
Key Findings
Study Design
Study Limitations
Clinical Significance
The trial results indicate that sildenafil does not provide clinical benefit in managing severe early-onset fetal growth restriction. The investigators concluded that sildenafil should not be prescribed for this condition outside of controlled research settings.
Historical Context
The STRIDER (Sildenafil TheRapy In Dismal prognosis Early-onset fetal growth Restriction) collaboration was established to evaluate whether the vasodilator properties of the phosphodiesterase type 5 inhibitor sildenafil could improve uteroplacental perfusion. Despite promising results in early small-scale studies and animal models, the international consortium trials ultimately failed to demonstrate efficacy and, in some international arms, raised concerns regarding neonatal safety.
Guided Discussion
High-yield insights from every perspective
Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor. What is the physiological mechanism by which this class of drug was hypothesized to improve fetal growth in cases of severe placental insufficiency?
Key Response
Sildenafil prevents the breakdown of cyclic guanosine monophosphate (cGMP), which enhances the vasodilatory effects of nitric oxide. In the context of fetal growth restriction (FGR), it was hypothesized that sildenafil would decrease uterine artery resistance and increase blood flow to the placenta (the 'placental bed'), thereby improving the delivery of oxygen and nutrients to the fetus.
In the management of a pregnancy complicated by severe early-onset FGR (<27 weeks), how should the findings of the STRIDER trial influence your response to a patient asking about experimental medications to 'help the baby grow'?
Key Response
The STRIDER trial provides high-quality evidence that sildenafil (25 mg TID) does not prolong pregnancy or improve perinatal survival compared to placebo. Residents should counsel patients that there are currently no proven pharmacological treatments to reverse FGR. Management should focus on intensive surveillance (umbilical artery and ductus venosus Doppler) and optimized delivery timing, rather than off-label use of sildenafil which has shown no benefit and potential safety concerns in related trials.
The STRIDER UK trial was part of an international consortium. How do you reconcile the neutral results of this trial with the previous meta-analyses of smaller studies that suggested a potential benefit in birthweight and pregnancy prolongation?
Key Response
This illustrates the 'small study effect' and publication bias common in early-phase research. Smaller, non-blinded studies often overstate effect sizes. STRIDER, as a large, multicentre, double-blind RCT, was powered to detect a clinically meaningful difference (1 week prolongation) and found none, suggesting that the earlier observed benefits were likely due to chance, lack of rigorous blinding, or heterogeneity in the FGR phenotypes included.
STRIDER failed to show a difference in the primary outcome of pregnancy prolongation. Does this negative result signify the end of the 'angiogenic/vasodilatory' hypothesis for treating placental insufficiency, or does it point toward a failure in the timing of intervention?
Key Response
This is a critical teaching point regarding 'irreversible pathology.' By the time severe FGR is diagnosed at 22-30 weeks with abnormal Dopplers, the placental vascular architecture is often already fundamentally malformed (e.g., poor spiral artery remodeling). Sildenafil acts on vascular tone, but cannot correct structural placental defects. Future research may need to focus on first-trimester prevention (like aspirin) rather than mid-gestation rescue.
Scholarly Review
Critical appraisal through the lens of expert reviewers and guideline development
Evaluate the choice of 'prolongation of pregnancy' as the primary endpoint in the STRIDER trial. What are the statistical risks of using a time-to-event surrogate in a population where delivery is often physician-indicated rather than spontaneous?
Key Response
In FGR trials, the duration of pregnancy is highly influenced by clinician behavior (protocolized delivery for Doppler changes) rather than just biological drug effect. This 'interventional bias' can mask a drug's true effect. A PhD researcher would argue for co-primary endpoints or a composite neonatal morbidity index that accounts for the trade-off between gaining maturity and the risk of continuing a pregnancy in a hostile intrauterine environment.
As a reviewer, if the STRIDER UK trial reported neutral results but a concurrent sister trial (STRIDER Holland) was stopped early for safety concerns (neonatal pulmonary hypertension), how would you ensure the manuscript's discussion properly contextualizes the risk-benefit ratio for the reader?
Key Response
An editor must ensure the paper doesn't just state 'no benefit' but also addresses 'potential harm.' Even if the UK arm didn't see a statistically significant increase in pulmonary hypertension, the discussion must integrate data from the broader consortium to prevent a 'neutral' finding from being misinterpreted as a 'safe' finding, especially when the efficacy is nil.
Given the STRIDER results, what level of recommendation should be assigned to sildenafil in clinical practice guidelines, and how does this compare to current ACOG or RCOG recommendations for FGR?
Key Response
STRIDER provides Level 1a evidence against the use of sildenafil for FGR. Current guidelines (like RCOG Green-top 31 or SMFM FGR guidelines) do not recommend sildenafil outside of research trials. Based on STRIDER, committees should issue a 'Strong Recommendation Against' its use in clinical practice, moving it from the 'experimental' category to the 'not recommended' category to prevent further off-label use that carries no benefit and potential risk.
Clinical Landscape
Noteworthy Related Trials
STRIDER NZAus Trial
Tested
Sildenafil citrate 25mg three times daily
Population
Pregnant women with early-onset severe fetal growth restriction
Comparator
Placebo
Endpoint
Survival to discharge from neonatal intensive care unit
STRIDER UK Trial
Tested
Sildenafil citrate 25mg three times daily
Population
Pregnant women with severe early-onset fetal growth restriction
Comparator
Placebo
Endpoint
Time from randomisation to birth
Dutch STRIDER Trial
Tested
Sildenafil citrate 25mg three times daily
Population
Pregnant women with severe early-onset fetal growth restriction
Comparator
Placebo
Endpoint
Perinatal mortality
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