Withdrawing Approval of Makena - A Proposal from the FDA Center for Drug Evaluation and Research

Regulatory histories of recently withdrawn ovarian cancer treatment indications of 3 PARP inhibitors in the US and Europe: lessons for the accelerated approval pathway

Background

Withdrawals of drug indications may reveal potential inadequacies in the regulatory approval processes of new drugs. Understanding potential weaknesses of the regulatory approval process is paramount given the increasing use of expedited pathways. In this paper, we focus on three poly-ADP-ribose polymerase inhibitors (olaparib, rucaparib and niraparib) for the treatment of women with heavily pretreated, recurrent ovarian cancer, which were eventually withdrawn.

Methods

We use a comparative case study approach to evaluate the regulatory histories of these drug indications in the US and Europe.

Results

Two drug indications benefited from the FDA's accelerated approval pathway, which explicitly lowers the bar for evidence of efficacy at the time of approval. Following accelerated approval, manufacturers are mandated to conduct post-marketing studies to confirm clinical benefit. The FDA granted accelerated approval to olaparib and rucaparib based on data on surrogate endpoints and converted the approval to regular approval after the submission of additional data on surrogate endpoints from one of two required confirmatory trials, that is, without data on clinical benefit. Niraparib directly received regular approval based only on data on a surrogate endpoint. By contrast, the EMA granted conditional marketing authorisation to rucaparib and was quicker to restrict usage than the FDA.

Conclusion

The regulatory histories of these drug indications highlight the need to reform the accelerated approval pathway by ensuring that post-marketing requirements are followed, and that regular approval is only based on evidence of clinical benefit.

Randomized controlled trials: not always the "gold standard" for evidence in obstetrics and gynecology

Randomized controlled trials are considered the "gold standard" for therapeutic interventions, and it is not uncommon for sweeping changes in medical practice to follow positive results from such trials. However, randomized controlled trials are not without their limitations. Physicians frequently view randomized controlled trials as infallible, whereas they tend to dismiss evidence derived from sources other than randomized controlled trials as less credible or reliable. In several situations in obstetrics and gynecology, there are no randomized controlled trials to help guide the clinician. In these circumstances, it is important to evaluate the entire body of evidence including observational studies, rather than dismiss interventions altogether simply because no randomized controlled trials exist. Randomized controlled trials and observational studies should be viewed as complementary rather than at odds with each other. Some reversals in widely adopted clinical practice have recently been implemented following subsequent studies that contradicted the outcomes of major randomized controlled trials. The most notable of these was the withdrawal from the market of 17-hydroxyprogesterone caproate for preterm birth prevention. Such reversals could potentially have been averted if the inherent limitations of randomized controlled trials were carefully considered before implementing these universal practice changes. This Clinical Opinion underscores the limitations of an exclusive reliance on randomized controlled trials while disregarding other evidence in determining how best to care for patients. Solutions are proposed that advocate that clinicians adopt a more balanced perspective that considers the entirety of the available medical evidence and the individual patient characteristics, needs, and wishes.

Integrative analysis of noncoding mutations identifies the druggable genome in preterm birth

Preterm birth affects ~10% of pregnancies in the US. Despite familial associations, identifying at-risk genetic loci has been challenging. We built deep learning and graphical models to score mutational effects at base resolution via integrating the pregnant myometrial epigenome and large-scale patient genomes with spontaneous preterm birth (sPTB) from European and African American cohorts. We uncovered previously unidentified sPTB genes that are involved in myometrial muscle relaxation and inflammatory responses and that are regulated by the progesterone receptor near labor onset. We studied genomic variants in these genes in our recruited pregnant women administered progestin prophylaxis. We observed that mutation burden in these genes was predictive of responses to progestin treatment for preterm birth. To advance therapeutic development, we screened ~4000 compounds, identified candidate molecules that affect our identified genes, and experimentally validated their therapeutic effects on regulating labor. Together, our integrative approach revealed the druggable genome in preterm birth and provided a generalizable framework for studying complex diseases.

What now? A critical evaluation of over 20 years of clinical and research experience with 17-alpha hydroxyprogesterone caproate for recurrent preterm birth prevention

Spontaneous preterm birth is multifactorial, and underlying etiologies remain incompletely understood. Supplementation with progestogens, including 17-alpha hydroxyprogesterone caproate has been a mainstay of prematurity prevention strategies in the United States in the last 2 decades. Following a recent negative confirmatory trial, 17-alpha hydroxyprogesterone caproate was withdrawn from the US market and is currently available only through clinical research studies. This expert review summarized clinical and research data regarding the use of 17-alpha hydroxyprogesterone caproate in the United States from 2003 to 2023 for recurrent prematurity prevention. In 17-alpha hydroxyprogesterone caproate. The history of the use, mechanisms of action, clinical trial results, and efficacy by clinical and biologic criteria of 17-alpha hydroxyprogesterone caproate are presented. We report that disparate findings and conclusions between similarly designed rigorous studies may reflect differences in a priori risk and population incidence and extreme care should be taken in interpreting the studies and making decisions regarding efficacy of 17-alpha hydroxyprogesterone caproate for the prevention of preterm birth. The likelihood of improved obstetrical outcomes after receiving 17-alpha hydroxyprogesterone caproate may vary by clinical factors (eg, body mass index), plasma drug concentrations, and genetic factors, although the identification of individuals most likely to benefit remains imperfect. It is crucial for the medical community to recognize the importance of preserving the decades-long efforts invested in preventing recurrent preterm birth in the United States. Moreover, it is important that we thoroughly and thoughtfully evaluate 17-alpha hydroxyprogesterone caproate as a promising contender for future well-executed prematurity studies.

Rematching on-the-fly: Sequential matched randomization and a case for covariate-adjusted randomization

Covariate-adjusted randomization (CAR) can reduce the risk of covariate imbalance and, when accounted for in analysis, increase the power of a trial. Despite CAR advances, stratified randomization remains the most common CAR method. Matched randomization (MR) randomizes treatment assignment within optimally identified matched pairs based on covariates and a distance matrix. When participants enroll sequentially, sequentially matched randomization (SMR) randomizes within matches found "on-the-fly" to meet a pre-specified matching threshold. However, pre-specifying the ideal threshold can be challenging and SMR yields less-optimal matches than MR. We extend SMR to allow multiple participants to be randomized simultaneously, to use a dynamic threshold, and to allow matches to break and rematch if a better match later enrolls (sequential rematched randomization; SRR). In simplified settings and a real-world application, we assess whether these extensions improve covariate balance, estimator/study efficiency, and optimality of matches. We investigate whether adjusting for more covariates can be detrimental upon covariate balance and efficiency as is the case of traditional stratified randomization. As secondary objectives, we use the case study to assess how SMR schemes compare side-by-side with common and related CAR schemes and whether adjusting for covariates in the design can be as powerful as adjusting for covariates in a parametric model. We find each SMR extension, individually and collectively, to improve covariate balance, estimator efficiency, study power, and quality of matches. We provide a case-study where CAR schemes with randomization-based inference can be as and more powerful than non-CAR schemes with parametric adjustment for covariates.

New medicines for spontaneous preterm birth prevention and preterm labour management: landscape analysis of the medicine development pipeline

BACKGROUND

There are few medicines in clinical use for managing preterm labor or preventing spontaneous preterm birth from occurring. We previously developed two target product profiles (TPPs) for medicines to prevent spontaneous preterm birth and manage preterm labor. The objectives of this study were to 1) analyse the research and development pipeline of medicines for preterm birth and 2) compare these medicines to target product profiles for spontaneous preterm birth to identify the most promising candidates.

METHODS

Adis Insight, Pharmaprojects, WHO international clinical trials registry platform (ICTRP), PubMed and grant databases were searched to identify candidate medicines (including drugs, dietary supplements and biologics) and populate the Accelerating Innovations for Mothers (AIM) database. This database was screened for all candidates that have been investigated for preterm birth. Candidates in clinical development were ranked against criteria from TPPs, and classified as high, medium or low potential. Preclinical candidates were categorised by product type, archetype and medicine subclass.

RESULTS

The AIM database identified 178 candidates. Of the 71 candidates in clinical development, ten were deemed high potential (Prevention: Omega-3 fatty acid, aspirin, vaginal progesterone, oral progesterone, L-arginine, and selenium; Treatment: nicorandil, isosorbide dinitrate, nicardipine and celecoxib) and seven were medium potential (Prevention: pravastatin and lactoferrin; Treatment: glyceryl trinitrate, retosiban, relcovaptan, human chorionic gonadotropin and Bryophyllum pinnatum extract). 107 candidates were in preclinical development.

CONCLUSIONS

This analysis provides a drug-agnostic approach to assessing the potential of candidate medicines for spontaneous preterm birth. Research should be prioritised for high-potential candidates that are most likely to meet the real world needs of women, babies, and health care professionals.

β3 Receptor Signaling in Pregnant Human Myometrium Suggests a Role for β3 Agonists as Tocolytics

Preterm labor leading to preterm birth is the leading cause of infant morbidity and mortality. At the present time, nothing can reliably halt labor once it begins. The knowledge that agonists of the β2 adrenergic receptor relax airway smooth muscle and are effective in the treatment of asthma led to the notion that β2 mimetics would prevent preterm birth by relaxing uterine smooth muscle. The activation of cAMP-dependent protein kinase by β2 receptors is unable to provide meaningful tocolysis. The failure of β2 agonists such as ritodrine and terbutaline to prevent preterm birth suggests that the regulation of uterine smooth muscle is disparate from that of airway. Other smooth muscle quiescent-mediating molecules, such as nitric oxide, relax vascular smooth muscle in a cGMP-protein kinase G-dependent manner; however, nitric oxide activation of protein kinase G fails to explain the relaxation of the myometrium to nitric oxide. Moreover, nitric oxide-mediated relaxation is blunted in preterm labor, and thus, for this reason and because of the fall in maternal blood pressure, nitric oxide cannot be employed as a tocolytic. The β3 adrenergic receptor-mediated relaxation of the human myometrium is claimed to be cAMP-dependent protein kinase-dependent. This is scientifically displeasing given the failure of β2 agonists as tocolytics and suggests a non-canonical signaling role for β3AR in myometrium. The addition of the β3 agonist mirabegron to pregnant human myometrial strips in the tissue bath relaxes oxytocin-induced contractions. Mirabegron stimulates nitric oxide production in myometrial microvascular endothelial cells, and the relaxation of uterine tissue in vitro is partially blocked by the addition of the endothelial nitric oxide synthase blocker Nω-Nitro-L-arginine. Recent data suggest that both endothelial and smooth muscle cells respond to β3 stimulation and contribute to relaxation through disparate signaling pathways. The repurposing of approved medications such as mirabegron (Mybetriq™) tested in human myometrium as uterine tocolytics can advance the prevention of preterm birth.

Progesterone and its receptor signaling in cervical remodeling: Mechanisms of physiological actions and therapeutic implications

The remodeling of the cervix from a closed rigid structure to one that can open sufficiently for passage of a term infant is achieved by a complex series of molecular events that in large part are regulated by the steroid hormones progesterone and estrogen. Among hormonal influences, progesterone exerts a dominant role for most of pregnancy to initiate a loss of tissue strength yet maintain competence in a phase termed softening. Equally important are the molecular events that abrogate progesterone function in late pregnancy to allow a loss of tissue competence and strength during cervical ripening and dilation. In this review, we focus on current understanding by which progesterone receptor signaling for the majority of pregnancy followed by a loss/shift in progesterone receptor action at the end of pregnancy, collectively ensure cervical remodeling as necessary for successful parturition.

Preterm Birth Therapies to Target Inflammation

Preterm birth (PTB; defined as delivery before 37 weeks of pregnancy) is the leading cause of morbidity and mortality in infants and children aged <5 years, conferring potentially devastating short- and long-term complications. Despite extensive research in the field, there is currently a paucity of medications available for PTB prevention and treatment. Over the past few decades, inflammation in gestational tissues has emerged at the forefront of PTB pathophysiology. Even in the absence of infection, inflammation alone can prematurely activate the main components of parturition resulting in uterine contractions, cervical ripening and dilatation, membrane rupture, and subsequent PTB. Mechanistic studies have identified critical elements of the complex inflammatory molecular pathways involved in PTB. Here, we discuss therapeutic options that target such key mediators with an aim to prevent, postpone, or treat PTB. We provide an overview of more traditional therapies that are currently used or being tested in humans, and we highlight recent advances in preclinical studies introducing novel approaches with therapeutic potential. We conclude that urgent collaborative action is required to address the unmet need of developing effective strategies to tackle the challenge of PTB and its complications.

Medicare Spending on Drugs With Accelerated Approval

BACKGROUND

The U.S. Food and Drug Administration provides accelerated approval to drugs on the basis of surrogate end points deemed to be "reasonably likely" to predict clinical benefit. To receive full approval, drugs must complete a confirmatory trial. Although most accelerated approved drugs ultimately receive full approval, others remain on the market without full approval for many years, and some are withdrawn before full approval is granted. Until confirmatory trials are completed and full approval is granted, there is uncertainty surrounding each drug's clinical benefits.

OBJECTIVE

To estimate fee-for-service Medicare payments on accelerated approved drugs without full approvals.

DESIGN

Cross-sectional analysis.

SETTING

Fee-for-service Medicare Part B and Part D drug claims in 2019.

PARTICIPANTS

Beneficiaries enrolled in Medicare Part B and Part D plans.

MEASUREMENTS

Medicare spending for drugs treating accelerated approved indications without full approval, beneficiary spending, and drug characteristics.

RESULTS

In 2019, 45 drugs associated with 69 accelerated approved indications lacked full approval. Of those, the fee-for-service Medicare program spent $1.2 billion on 36 drugs across 55 indications. Medicare beneficiaries had $209 million in out-of-pocket spending on these drugs. Oncology drugs represented 82% of these indications and 72% of the Medicare spending. Extrapolating to Medicare Advantage, total Medicare spending on these drugs in 2019 was $1.8 billion.

LIMITATIONS

The study drugs may have clinical benefit and may come to receive full approval after this analysis. The algorithm used to identify accelerated approved indications is novel. Generalizability to other years is unclear.

CONCLUSION

In 2019, fee-for-service Medicare spent $1.2 billion on accelerated approved drugs without full approval. Medicare should adjust incentives to encourage sponsors to complete confirmatory trials as soon as possible.

PRIMARY FUNDING SOURCE

Laura and John Arnold Foundation.

Changes in the Use of Hydroxyprogesterone Caproate Injection After Confirmatory Trial Failure

This cross-sectional study examines changes in hydroxyprogesterone caproate fills from 2010 through 2020.

In utero exposure to 17α-hydroxyprogesterone caproate and risk of cancer in offspring

BACKGROUND

17α-hydroxyprogesterone caproate is a synthetic progestogen initially approved in the 1950s to treat gynecologic and obstetrical conditions. Despite continued concerns about safety and short-term efficacy regarding the use of 17α-hydroxyprogesterone caproate for the prevention of preterm birth in pregnant women, little is known about the long-term effects of 17α-hydroxyprogesterone caproate on the health of the offsprings.

OBJECTIVE

To examine the association between in utero exposure to 17α-hydroxyprogesterone caproate and the risk of cancer in the offspring.

STUDY DESIGN

The Child Health and Development Studies was a population-based cohort of >18,000 mother-child dyads receiving prenatal care in the Kaiser Foundation Health Plan (Oakland, CA) between 1959 and 1966. Clinical information was abstracted from the mothers' medical records beginning 6 months before pregnancy through delivery. We identified the number and timing of 17α-hydroxyprogesterone caproate injections during pregnancy. Incident cancers diagnosed in the offspring were ascertained through 2019 by linkage to the California Cancer Registry. We used the Cox proportional hazard models to estimate the adjusted hazard ratios and their 95% confidence intervals, with the follow-up time accrued from the date of birth through the date of cancer diagnosis, death, or last contact.

RESULTS

A total of 1008 offspring were diagnosed with cancer over 730,817 person-years of follow-up. Approximately 1.0% of the offspring (n=234) were exposed in utero to 17α-hydroxyprogesterone caproate. Exposure in the first trimester was associated with an increased risk of any cancer (adjusted hazard ratio, 2.57; 95% confidence interval, 1.59-4.15), and the risk increased with the number of injections (1-2 injections: adjusted hazard ratio, 1.80; 95% confidence interval, 1.12-2.90; ≥3 injections: adjusted hazard ratio, 3.07; 95% confidence interval, 1.34-7.05). Exposure in the second or third trimester conferred an additional risk for the male (adjusted hazard ratio, 2.59; 95% confidence interval, 1.07-6.28) but not for the female (adjusted hazard ratio, 0.30; 95% confidence interval, 0.04-1.11) offspring. The risk of colorectal (adjusted hazard ratio, 5.51; 95% confidence interval, 1.73-17.59), prostate (adjusted hazard ratio, 5.10; 95% confidence interval, 1.24-21.00), and pediatric brain (adjusted hazard ratio, 34.72; 95% confidence interval, 7.29-164.33) cancer was higher in the offspring first exposed to 17α-hydroxyprogesterone caproate in the first trimester than the offspring not exposed.

CONCLUSION

Caution using 17α-hydroxyprogesterone caproate in early pregnancy is warranted, given the possible link with cancer in the offspring.

17-Alpha-Hydroxyprogesterone vs. Placebo for Preventing of Recurrent Preterm Birth: A Systematic Review and Meta-Analysis of Randomized Trials

Background: Preterm birth (PTB) is a leading cause of neonatal morbidity and mortality. Objective: To estimate the effect of 17-alpha-hydroxyprogesterone caproate (17-OHPC) compared to placebo in singleton gestations for reducing the risk of recurrent PTB and neonatal morbidity and mortality. Work Design: Systematic review and meta-analysis. Search Strategy: Searching MEDLINE, Embase, Web of Science, SCOPUS, Cochrane Library, and clinical trial registries. Selection Criteria: Randomized controlled trials of singleton gestations with a history of PTB and treated with a weekly intramuscular injection of 17-OHPC or placebo. Data Collection and Analysis: A random meta-analysis model was performed for the PTB outcomes (<32, <35, and <37 weeks) and neonatal outcomes (neonatal death, grade 3 or 4 intraventricular hemorrhage, respiratory distress syndrome, bronchopulmonary dysplasia, necrotizing enterocolitis, and sepsis). Effect estimates were measured by relative risk ratio (RR) with a 95% confidence interval (CI). Main Results: Six works were included. There were no statistically significant reductions in the PTB risk following the use of 17-OHPC at <32 weeks (RR = 0.61, 95% CI: 0.13-2.77, and I ² = 39%), <35weeks (RR = 0.60, 95% CI: 0.10-3.67, and I ² = 51%), and <37 weeks (RR = 0.68, 95% CI: 0.46-1, and I ² = 75%). Furthermore, all the neonatal outcomes were statistically similar between the two groups. Conclusion: Treatment with 17-OHPC is not associated with reducing the risk of PTB or neonatal outcomes compared to placebo.

Raising Medicaid Rebates For Drugs With Accelerated Approval

Through the Accelerated Approval Program, the Food and Drug Administration (FDA) may approve drugs that treat severe or life-threatening conditions on the basis of preliminary evidence of efficacy. Many of these drugs are made available at extremely high prices. In April 2021 the Medicaid and CHIP Payment and Access Commission endorsed a policy that would require manufacturers of drugs receiving accelerated approval to pay higher rebates to Medicaid until their drug's efficacy is demonstrated in confirmatory postapproval studies. We examined the impact of this policy by studying Medicaid spending on eighty-nine accelerated approval drugs during 2015-20. Medicaid spent an estimated $6.7 billion on these drugs after estimated rebates under existing rules. Raising base rebates from 23.1 percent to 30-80 percent could have saved Medicaid $0.6-$5.2 billion during this six-year period; raising inflationary rebates by two to four times would have had a smaller impact, creating savings of up to $0.9 billion. Accelerated approval drugs represent a small but growing percentage of Medicaid's total prescription drug spending. The policy evaluated in this study can offer important savings, but implementation must account for the fact that many of these drugs have additional indications with regular FDA approval.

Utilization, adherence, and outcomes of 17-alpha hydroxyprogesterone caproate for recurrent spontaneous preterm birth prevention

OBJECTIVE

To describe the use of and adherence to 17-alpha hydroxyprogesterone caproate (17-OHPC), explore factors associated with its utilization and adherence, and to investigate the outcomes of 17-OHPC in a real-world setting.

METHODS

The Decision Resources Group (DRG) database (1 January 2012-31 December 2017) was used to identify women with diagnosis of "history of preterm labor", aged 16-50 years old, had a singleton gestation, were continuously enrolled for at least 6 months and 9 months before and after the index date, respectively, and had a delivery outcome recorded. Adequate adherence was defined and compared using two approaches: (1) patients receiving at least 10 injections of 17-OHPC; (2) number of received injections/eligible number of injections ≥0.7. The outcome of 17-OHPC was evaluated by the incidence rate of preterm birth (PTB). Bivariate tests compared patients' characteristics with their use of and adherence to 17-OHPC, and examined the associations between 17-OHPC utilization and incidence of diabetes or hypertension. Stepwise logistic regression was conducted to assess the effect of adherence on the delivery outcome.

RESULTS

Of 28,339 patients meeting study criteria, 2585 (9.1%) had ≥1 claim for 17-OHPC. An increasing trend of utilization was observed from 2012 to 2017 (7.6-13.1%). The utilization rate was highest in the Southwest US (13.8%) (p < .001). Commercial insurance patients (9.6%) were more likely to use 17-OHPC than Medicaid patients (7.9%) (p < .001). Patients with higher Charlson Comorbidity Index (CCI) scores were less likely to use 17-OHPC. Of women prescribed 17-OHPC, 792 (30.6%) and 424 (16.4%) were adherent using two definitions, respectively. No difference in PTB rate was observed between adherers and non-adherers (definition 1: aOR = 0.97, 95% CI = 0.81-1.16; definition 2: aOR = 1.18, 95% CI = 0.95-1.48). No association was found between 17-OHPC and incidence of diabetes (p = .96); however, use of 17-OHPC was associated with a lower incidence rate of hypertension (p = .002).

CONCLUSIONS

17-OHPC utilization and adherence rates remain low. Insurance type and geographic region were associated with both utilization and adherence. There was no association between 17-OHPC adherence and effectiveness. More evidence is needed to determine if the use of 17-OHPC is advantageous in a sub-group of patients.

Landscape of Preterm Birth Therapeutics and a Path Forward

Preterm birth (PTB) remains the leading cause of infant morbidity and mortality. Despite 50 years of research, therapeutic options are limited and many lack clear efficacy. Tocolytic agents are drugs that briefly delay PTB, typically to allow antenatal corticosteroid administration for accelerating fetal lung maturity or to transfer patients to high-level care facilities. Globally, there is an unmet need for better tocolytic agents, particularly in low- and middle-income countries. Although most tocolytics, such as betamimetics and indomethacin, suppress downstream mediators of the parturition pathway, newer therapeutics are being designed to selectively target inflammatory checkpoints with the goal of providing broader and more effective tocolysis. However, the relatively small market for new PTB therapeutics and formidable regulatory hurdles have led to minimal pharmaceutical interest and a stagnant drug pipeline. In this review, we present the current landscape of PTB therapeutics, assessing the history of drug development, mechanisms of action, adverse effects, and the updated literature on drug efficacy. We also review the regulatory hurdles and other obstacles impairing novel tocolytic development. Ultimately, we present possible steps to expedite drug development and meet the growing need for effective preterm birth therapeutics.

Evaluating Progestogens for Preventing Preterm birth International Collaborative (EPPPIC): meta-analysis of individual participant data from randomised controlled trials

BACKGROUND

Preterm birth is a global health priority. Using a progestogen during high-risk pregnancy could reduce preterm birth and adverse neonatal outcomes.

METHODS

We did a systematic review of randomised trials comparing vaginal progesterone, intramuscular 17-hydroxyprogesterone caproate (17-OHPC), or oral progesterone with control, or with each other, in asymptomatic women at risk of preterm birth. We identified published and unpublished trials that completed primary data collection before July 30, 2016, (12 months before data collection began), by searching MEDLINE, Embase, CINAHL, the Maternity and Infant Care Database, and relevant trial registers between inception and July 30, 2019. Trials of progestogen to prevent early miscarriage or immediately-threatened preterm birth were excluded. Individual participant data were requested from investigators of eligible trials. Outcomes included preterm birth, early preterm birth, and mid-trimester birth. Adverse neonatal sequelae associated with early births were assessed using a composite of serious neonatal complications, and individually. Adverse maternal outcomes were investigated as a composite and individually. Individual participant data were checked and risk of bias assessed independently by two researchers. Primary meta-analyses used one-stage generalised linear mixed models that incorporated random effects to allow for heterogeneity across trials. This meta-analysis is registered with PROSPERO, CRD42017068299.

FINDINGS

Initial searches identified 47 eligible trials. Individual participant data were available for 30 of these trials. An additional trial was later included in a targeted update. Data were therefore available from a total of 31 trials (11 644 women and 16185 offspring). Trials in singleton pregnancies included mostly women with previous spontaneous preterm birth or short cervix. Preterm birth before 34 weeks was reduced in such women who received vaginal progesterone (nine trials, 3769 women; relative risk [RR] 0·78, 95% CI 0·68-0·90), 17-OHPC (five trials, 3053 women; 0·83, 0·68-1·01), and oral progesterone (two trials, 181 women; 0·60, 0·40-0·90). Results for other birth and neonatal outcomes were consistently favourable, but less certain. A possible increase in maternal complications was suggested, but this was uncertain. We identified no consistent evidence of treatment interaction with any participant characteristics examined, although analyses within subpopulations questioned efficacy in women who did not have a short cervix. Trials in multifetal pregnancies mostly included women without additional risk factors. For twins, vaginal progesterone did not reduce preterm birth before 34 weeks (eight trials, 2046 women: RR 1·01, 95% CI 0·84-1·20) nor did 17-OHPC for twins or triplets (eight trials, 2253 women: 1·04, 0·92-1·18). Preterm premature rupture of membranes was increased with 17-OHPC exposure in multifetal gestations (rupture <34 weeks RR 1·59, 95% CI 1·15-2·22), but we found no consistent evidence of benefit or harm for other outcomes with either vaginal progesterone or 17-OHPC.

INTERPRETATION

Vaginal progesterone and 17-OHPC both reduced birth before 34 weeks' gestation in high-risk singleton pregnancies. Given increased underlying risk, absolute risk reduction is greater for women with a short cervix, hence treatment might be most useful for these women. Evidence for oral progesterone is insufficient to support its use. Shared decision making with woman with high-risk singleton pregnancies should discuss an individual's risk, potential benefits, harms and practicalities of intervention. Treatment of unselected multifetal pregnancies with a progestogen is not supported by the evidence.

FUNDING

Patient-Centered Outcomes Research Institute.