Functional effects of 17alpha-hydroxyprogesterone caproate (17P) on human myometrial contractility in vitro

Vaginal progesterone for the prevention of recurrent spontaneous preterm birth

After the United States Food and Drug Administration pulled 17-alpha hydroxyprogesterone caproate from the market for its use in prevention of recurrent spontaneous preterm birth, national societies have had mixed recommendations regarding the management of patients with a singleton pregnancy and previous spontaneous preterm birth. Herein we highlight the randomized trial data and translational evidence supporting the use of vaginal progesterone for prevention of recurrent spontaneous preterm birth in singleton pregnancies. Prophylactic vaginal progesterone starting at 16 weeks and 0 days every night should be offered to patients with singletons and previous singleton spontaneous preterm birth regardless of cervical length, and continued along with placement of cerclage if a transvaginal ultrasound cervical length ≤25 mm is detected at <24 weeks.

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 Following a recent negative confirmatory trial, 17-alpha hydroxyprogesterone caproate was withdrawn from the US market and is currently available only through clinical research studies.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.

Progesterone, via yes-associated protein, promotes cardiomyocyte proliferation and cardiac repair

Objectives

The mechanisms responsible for the postnatal loss of mammalian cardiac regenerative capacity are not fully elucidated. The aim of the present study is to investigate the role of progesterone in cardiac regeneration and explore underlying mechanism.

Materials and Methods

Effect of progesterone on cardiomyocyte proliferation was analysed by immunofluorescent staining. RNA sequencing was performed to screen key target genes of progesterone, and yes‐associated protein (YAP) was knocked down to demonstrate its role in pro‐proliferative effect of progesterone. Effect of progesterone on activity of YAP promoter was measured by luciferase assay and interaction between progesterone receptor and YAP promoter by electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP). Adult mice were subjected to myocardial infarction, and then, effects of progesterone on adult cardiac regeneration were analysed.

Results

Progesterone supplementation enhanced cardiomyocyte proliferation in a progesterone receptor‐dependent manner. Progesterone up‐regulated YAP expression and knockdown of YAP by small interfering RNA reduced progesterone‐mediated cardiomyocyte proliferative effect. Progesterone receptor interacted with the YAP promoter, determined by ChIP and EMSA; progesterone increased luciferase activity of YAP promoter and up‐regulated YAP target genes. Progesterone administration also promoted adult cardiomyocyte proliferation and improved cardiac function in myocardial infarction.

Conclusion

Our data uncover a role of circulating progesterone withdrawal as a novel mechanism for the postnatal loss of mammalian cardiac regenerative potential. Progesterone promotes both neonatal and adult cardiomyocyte proliferation by up‐regulating YAP expression.

Vaginal progesterone, but not 17α-hydroxyprogesterone caproate, has antiinflammatory effects at the murine maternal-fetal interface

OBJECTIVE

Progestogen (vaginal progesterone or 17-alpha-hydroxyprogesterone caproate [17OHP-C]) administration to patients at risk for preterm delivery is widely used for the prevention of preterm birth (PTB). The mechanisms by which these agents prevent PTB are poorly understood. Progestogens have immunomodulatory functions; therefore, we investigated the local effects of vaginal progesterone and 17OHP-C on adaptive and innate immune cells implicated in the process of parturition.

STUDY DESIGN

Pregnant C57BL/6 mice received vaginal progesterone (1 mg per 200 μL, n = 10) or Replens (control, 200 μL, n = 10) from 13 to 17 days postcoitum (dpc) or were subcutaneously injected with 17OHP-C (2 mg per 100 μL, n = 10) or castor oil (control, 100 μL, n = 10) on 13, 15, and 17 dpc. Decidual and myometrial leukocytes were isolated prior to term delivery (18.5 dpc) for immunophenotyping by flow cytometry. Cervical tissue samples were collected to determine matrix metalloproteinase (MMP)-9 activity by in situ zymography and visualization of collagen content by Masson's trichrome staining. Plasma concentrations of progesterone, estradiol, and cytokines (interferon [IFN]γ, interleukin (IL)-1β, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12p70, keratinocyte-activated chemokine/growth-related oncogene, and tumor necrosis factor-α) were quantified by enzyme-linked immunosorbent assays. Pregnant mice pretreated with vaginal progesterone or Replens were injected with 10 μg of an endotoxin on 16.5 dpc (n = 10 each) and monitored via infrared camera until delivery to determine the effect of vaginal progesterone on the rate of PTB.

RESULTS

The following results were found: (1) vaginal progesterone, but not 17OHP-C, increased the proportion of decidual CD4+ regulatory T cells; (2) vaginal progesterone, but not 17OHP-C, decreased the proportion of decidual CD8+CD25+Foxp3+ T cells and macrophages; (3) vaginal progesterone did not result in M1→M2 macrophage polarization but reduced the proportion of myometrial IFNγ+ neutrophils and cervical active MMP-9-positive neutrophils and monocytes; (4) 17OHP-C did not reduce the proportion of myometrial IFNγ+ neutrophils; however, it increased the abundance of cervical active MMP-9-positive neutrophils and monocytes; (5) vaginal progesterone immune effects were associated with reduced systemic concentrations of IL-1β but not with alterations in progesterone or estradiol concentrations; and (6) vaginal progesterone pretreatment protected against endotoxin-induced PTB (effect size 50%, P = 0.011).

CONCLUSION

Vaginal progesterone, but not 17OHP-C, has local antiinflammatory effects at the maternal-fetal interface and the cervix and protects against endotoxin-induced PTB.

Actions of progestins for the inhibition of cervical ripening and uterine contractions to prevent preterm birth

The importance of progesterone (P4) for maintenance of pregnancy, its role in cervical ripening and uterine contractions is at least partly established and therefore, not surprisingly, the basis for the concept to use P4 as a treatment for preterm birth. Due to the complexity of the condition of preterm birth there are still questions concerning the optimal population that might benefit, timing of treatment, dosage, vehicle and route of administration. Recently vaginal P4 and intramuscular 17-alpha-hydroxyprogesterone caproate (17P) have been used to prevent preterm birth in patients with a high risk for early delivery. The aim of this study was to assess cervical changes throughout pregnancy in rats and the timing of term and preterm delivery after various progestin treatments given by different routes and vehicles in hope of identifying better treatment regimens. This paper presents results that suggest that there are better routes of treatment than the vaginal route (e.g. topical), that the vehicle used in many of the clinical studies (Replens®) is not appropriate due to a low release of the steroid and consequently low uptake of P4, and that inhibition of birth is primarily due to inhibition of uterine contractility that can be achieved by supplementation of P4 but not with 17P.

Metabolism of 17-alpha-hydroxyprogesterone caproate by human placental mitochondria

Perfusion of 17-alpha-hydroxyprogesterone caproate (17HPC) via the maternal circuit of a dually perfused human placental lobule resulted in the extensive formation of 2 metabolites. On the other hand, human placental microsomes biotransformed 17HPC into 5 monohydroxylated metabolites, which did not correspond to those formed during perfusion. The goal of this investigation was to determine the subcellular localization of the enzymes responsible for the biotransformation of 17HPC during its perfusion in human placenta. Crude subcellular fractions of the human placental tissue were utilized. Six 17HPC metabolites were formed by the placental mitochondrial fraction, of which 4 were identical to those formed by the microsomes; whereas the other 2, namely MM and M₁₉, were formed by the mitochondrial fraction only. The latter metabolites were identical to those formed during 17HPC perfusion, as determined by liquid chromatography-mass spectrometry (LC-MS) analysis. Therefore, these data strongly suggest that the enzymes responsible for the biotransformation of 17HPC during its perfusion are predominantly localized in human placental mitochondria.

17 α-Hydroxyprogesterone caproate (Makena™): in the prevention of preterm birth

17 α-hydroxyprogesterone caproate is a synthetic progestin of which there is now a US FDA-approved formulation available for intramuscular administration (Makena™) to reduce the risk of preterm birth. Intramuscular 17 α-hydroxyprogesterone caproate (identical in formulation and manufacturing process to Makena™, thus hereafter referred to as Makena™) 250 mg once weekly, initiated at 16-20 weeks' gestation, was effective in reducing the risk of preterm birth in women with a singleton pregnancy at high risk of delivering preterm in a large, well designed, placebo-controlled trial (n = 463 randomized). Rates of delivery before 37 (primary endpoint), 35, or 32 weeks' gestation were significantly lower with Makena™ than with placebo, corresponding to relative risk reductions of 34%, 33%, and 42%, respectively. The benefit of the drug in reducing the risk of preterm birth was observed when deliveries were spontaneous (but not when indicated because of complications) and regardless of maternal race. In addition, there was a significantly lower rate of several adverse fetal/neonatal outcomes among infants of women who received Makena™ than among infants of placebo recipients, including necrotizing enterocolitis, need for supplemental oxygen, birth weight of <2500 g, and intraventricular hemorrhage. Makena™ was generally well tolerated in pregnant women in this trial. Moreover, fetal exposure to the drug appeared to be safe according to a 2- to 5-year follow-up of the study, with no evidence of a detrimental effect of the drug on child neurodevelopment and a low overall incidence (≈2%) of reproductive or genital abnormalities that was not significantly different from placebo.

Progestin treatment for the prevention of preterm birth

Progestin supplementation appears to be a promising approach to both preventing initiation of preterm labor and treating it once it is already established, given the role of progesterone in maintaining pregnancy, as well as support from basic and clinical research. Progesterone and 17α-hydroxyprogesterone acetate slow the process of cervical ripening, and this is the rationale for prophylactic long-term progestin supplementation mostly studied so far. However, progesterone (but not 17α-hydroxyprogesterone acetate) also inhibits myometrial activity even after the cervix has already ripened. Moreover, these effects depend greatly on the vehicle used and the route of administration. Understanding different mechanisms of action, as well as the importance of progestin formulation, vehicle and route of administration, is the key to finding the optimal progestin treatment for prevention of preterm birth.

Effect of 17-alpha hydroxyprogesterone caproate on the production of tumor necrosis factor-alpha and the expression of cyclooxygenase-2 in lipopolysaccharide-treated gravid human myometrial explants

OBJECTIVE

To determine whether 17-alpha hydroxyprogesterone (17-OHPC) alters tumor necrosis factor-alpha (TNF-alpha) production and the expression of cyclooxygenase type 2 (COX-2) in myometrium exposed to lipopolysaccharide (LPS).

STUDY DESIGN

Lower segment myometrial biopsies were obtained from non-laboring patients at term. Tissues were cultured in serum-free media with 17-OHPC (1 microM) and LPS (1 microg/ml), either alone or in combination. At 24 h, the production of tumor necrosis factor-alpha (TNF-alpha) and the expression of COX-2 was determined using enzyme linked immunosorbent assay and real-time (RT-PCR). Statistical analysis was performed using non-parametric testing. A P-value of <0.05 was considered significant.

RESULT

17-OHPC had no effect on TNF-alpha production and COX-2 expression when compared with untreated myometrial explants (P=0.61 and P=0.95). LPS induced production of TNF-alpha (P=0.03) and expression of COX-2 (P=0.02). Treatment with 17-OHPC did not block LPS-induced TNF-alpha production (P=0.37) or COX-2 expression (P=0.12).

CONCLUSION

In this pilot study, 17-OHPC did not affect the production of TNF-alpha or COX-2 expression in human myometrium.

Pharmacologic actions of progestins to inhibit cervical ripening and prevent delivery depend on their properties, the route of administration, and the vehicle

OBJECTIVE

The purpose of this study was to evaluate cervical changes and delivery at term during pregnancy in rats after various progestin treatments.

STUDY DESIGN

Pregnant rats were treated by various routes and vehicles with progesterone, 17-alpha-hydroxyprogesterone caproate (17P), R5020, and RU-486. Delivery time was determined and cervical ripening was assessed in vivo by collagen light-induced fluorescence.

RESULTS

The cervix is rigid in the progesterone injection, 17P, and vaginal R5020 groups vs controls. Vaginal progesterone had no effect. RU-486 treatment softened the cervix during preterm delivery. Only subcutaneous injected progesterone, R5020 (subcutaneous and vaginal), and topical progesterone in sesame and fish oil inhibits delivery. Delivery is not changed by subcutaneous injection of 17P, vaginal progesterone, oral progesterone, and topical progesterone in Replens (Crinone; Columbia Labs, Livingston, NJ).

CONCLUSION

Inhibition of cervical ripening and delivery by progestins depends on many factors that include their properties, the route of administration, and the vehicle. This study suggests reasons that the present treatments for preterm labor are not efficacious.

Embryo–fetal toxicity signals for 17α-hydroxyprogesterone caproate in high-risk pregnancies: A review of the non-clinical literature for embryo–fetal toxicity with progestins

OBJECTIVE

A large National Institutes of Health (NIH) study showed that pharmacy-compounded 17alpha-hydroxyprogesterone caproate (17-OHP-C) reduced the incidence of preterm birth. The study results included a signal that 17-OHP-C may be associated with an increase in the rate of miscarriages and stillbirths. The most probable cause of an increased incidence of miscarriage/stillbirths may be the use of 17-OHP-C in high-risk patients. The current search of the non-clinical literature was performed to identify whether there were any signals from studies in animals that might suggest concerns for the safe use of progestins generally, and 17-OHP-C specifically, in the prevention of preterm birth in humans.

METHODS

An extensive literature search was performed for progesterone, 17-hydroxyprogesterone, and 17-OHP-C, using Medline and Toxline databases, textbooks, and then the obtained publications. Because 17-OHP-C does not have a standardized clinical formulation or optimal route of administration identified, all formulations, vehicles, routes and doses were included in the search, as well as treatment during any stage of pregnancy. All publications obtained were reviewed for relevancy; those in German, French, Italian or Russian were translated.

RESULTS

None of the relevant non-clinical studies conducted in mice, rats, rabbits, guinea pigs, horses or non-human primates met current standards for determining reproductive and developmental effects as part of the process of drug development. Most studies focused on the potential of 17-OHP-C for teratogenicity. Many studies used supra-pharmacologic and/or high multiples of human exposure in their study design. Overall, 17-OHP-C was consistently shown to be less potent than progesterone, and neither progesterone nor 17-OHP-C consistently adversely affected maternal weight, embryo-fetal viability or caused malformations. One study in rhesus monkeys raises concerns because resorption/abortion occurred at the human equivalent dose of 17-OHP-C, 10 mg/kg; this finding did not occur in cynomolgus monkeys. The absence of information regarding the serum levels of both progesterone and 17-OHP-C in the animal studies and in humans, as well as presumed inter-species metabolic differences, make it difficult to conclude that the findings with 17-OHP-C in rhesus monkeys and the signal in the NIH trial are related. A few studies in rats raised questions regarding potential effects on postnatal development, but in the absence of better study designs, the relevancy of these findings to human risk are also questionable at best.

CONCLUSION

There is a signal for embryo-fetal toxicity associated with 17-OHP-C in the two largest clinical trials conducted to date; there is also a signal for embryo-fetal toxicity with 17-OHP-C in rhesus monkeys and possibly one in rodent species. The relationship between these signals is unclear given the absence of state-of-the-art reproductive toxicology studies and human pharmacokinetic studies.

PROGESTERONE AND THE CONTROL OF HUMAN PREGNANCY AND PARTURITION

Almost 80 years ago George Corner and colleagues provided the first evidence that progesterone maintains pregnancy and that it does so, at least in part, by promoting myometrial relaxation. In the 1950s, Arpad Csapo proposed the “progesterone block hypothesis”, which posits that progesterone maintains pregnancy by promoting myometrial relaxation and that its withdrawal initiates a cascade of hormonal interactions that transforms the myometrium to a highly contractile state leading to the onset of labour. Csapo later proposed that contractility of the pregnant myometrium is determined by the balance between relaxation induced by progesterone and contraction induced by a cohort of signals including oestrogens, uterine distention and stimulatory uterotonins such as prostaglandins (PGs) and oxytocin (OT). According to this “seesaw” hypothesis, progesterone promotes myometrial relaxation by directly inducing relaxation and/or by inhibiting the production of, or myometrial responsiveness to, stimulatory uterotonins. These landmark concepts, though derived from studies of experimental animals, form the foundation for current understanding of progesterone's role in the physiology of human pregnancy. Remarkable progress has been made over the last 20–30 years in understanding the signal transduction pathways through which steroid hormones affect target cells. This knowledge has broadened the scope of Csapo's original paradigms and we are now beginning to unravel the specific signaling pathways and molecular interactions by which progesterone affects human myometrium and how its actions are controlled at the functional level. This is important for the development of progestin-based therapeutics for the prevention or suppression of preterm labour and preterm birth. Here we review recent progress in understanding the mechanisms by which progesterone sustains pregnancy and in particular how it promotes myometrial relaxation, how its relaxatory actions are nullified at parturition, and the hormonal interactions that induce progesterone withdrawal to determine the timing of human birth.

Progesterone, but not 17-alpha-hydroxyprogesterone caproate, inhibits human myometrial contractions

OBJECTIVE

The aim was to determine whether progesterone (P4) or 17-alpha-hydroxyprogesterone caproate (17P) directly inhibit human uterine contractility in vitro and thereby clarify their mechanisms of action.

STUDY DESIGN

Myometrial tissues were suspended in organ chambers and exposed for 2 to 20 hours to varying concentrations of P4 or 17P or solvent. Contractile activity was registered, stored, and analyzed. Dose response curves were then generated for P4 or 17P at various times.

RESULTS

P4 significantly inhibited spontaneous contractility dose dependently. The inhibition was not blocked by RU486 but was reversible after washing. Surprisingly, 17P dose dependently stimulated contractility. HPLC and GC-MS methods were used to determine the detectable concentrations of progestins in the baths.

CONCLUSION

P4, at concentrations equivalent to those present in the placenta and uterus, inhibit spontaneous myometrial contractility in vitro by nongenomic mechanisms.

Preventing cervical ripening: the primary mechanism by which progestational agents prevent preterm birth?

OBJECTIVE

Recent clinical trials suggest that progestational agents may prevent preterm birth, specifically in women with short cervices. These studies sought to assess novel pathways by which progestational agents (PAs) may modify signal transduction pathways that are involved in cervical ripening.

STUDY DESIGN

A microarray analysis was performed on pregnant mouse cervix that was exposed to a MPA. Appropriate microarray and cluster analyses were performed. Target genes of interest were investigated in both PA- and inflammation-exposed cervices by quantitative polymerase chain reaction and immunohistochemistry.

RESULTS

Microarray analysis identified both the previously recognized and novel pathways that are involved in cervical ripening. PAs differentially regulate expression of claudin-2, hyaluronan synthase 2, and lipocalin 2. Claudin expression is significantly decreased by inflammation, which is prevented by PAs.

CONCLUSION

PAs significantly modulate gene expression in the cervix in the presence and absence of inflammation. The regulation of these pathways, specifically claudin proteins, may be a critical mechanism by which PAs prevent preterm birth, especially in women with premature cervical shortening.

Human decidual cell Toll-like receptor signaling in response to endotoxin: the effect of progestins

OBJECTIVE

The purpose of this study was to determine whether progesterone, 17-alpha-hydroxyprogesterone, and 17-alpha hydroxyprogesterone caproate modulate the Toll-like receptor (TLR) pathway in the response of decidua to lipopolysaccharide.

STUDY DESIGN

Cultured human decidual cells were incubated under control conditions, lipopolysaccharide alone, or pretreatment with each of the 3 progestins. Relative expression of 113 genes in the TLR pathway was determined by microarray.

RESULTS

We failed to demonstrate a suppression of TLR gene pathway expression in human decidual cells in response to lipopolysaccharide when the cells are pretreated with progestins. Pretreatment with each progestin before lipopolysaccharide resulted in a relative increase in the expression of the proapoptotic molecule, CASP8. There were no differences among the progestins.

CONCLUSION

Our data do not support suppression of TLR pathways as a mechanism for the benefit of 17-alpha hydroxyprogesterone caproate. Increased CASP8 gene expression raises the possibility that progestins "prime" the decidual cell to respond with a NFkappaB-mediated inflammatory response.

Progesterone vaginal gel for the reduction of recurrent preterm birth: primary results from a randomized, double-blind, placebo-controlled trial

OBJECTIVE

Preterm birth is the leading cause of perinatal morbidity and mortality worldwide. Treatment of preterm labor with tocolysis has not been successful in improving infant outcome. The administration of progesterone and related compounds has been proposed as a strategy to prevent preterm birth. The objective of this trial was to determine whether prophylactic administration of vaginal progesterone reduces the risk of preterm birth in women with a history of spontaneous preterm birth.

METHODS

This randomized, double-blind, placebo- controlled, multinational trial enrolled and randomized 659 pregnant women with a history of spontaneous preterm birth. Between 18 + 0 and 22 + 6 weeks of gestation, patients were assigned randomly to once-daily treatment with either progesterone vaginal gel or placebo until either delivery, 37 weeks' gestation or development of preterm rupture of membranes. The primary outcome was preterm birth at </= 32 weeks of gestation. The trial was analyzed using an intent-to-treat strategy.

RESULTS

Baseline characteristics were similar in the two treatment groups. Progesterone did not decrease the frequency of preterm birth at </= 32 weeks. There was no difference between the groups with respect to the mean gestational age at delivery, infant morbidity or mortality or other maternal or neonatal outcome measures. Adverse events during the course of treatment were similar for the two groups.

CONCLUSION

Prophylactic treatment with vaginal progesterone did not reduce the frequency of recurrent preterm birth (</= 32 weeks) in women with a history of spontaneous preterm birth. The effect of progesterone administration in patients at high risk for preterm delivery as determined by methods other than history alone (e.g. sonographic cervical length) requires further investigation.

New research models and novel signal analysis in studies on preterm labor: a key to progress?

Preterm labor affects up to 20% of pregnancies, is considered a main cause of associated neonatal morbidity and mortality and is responsible for neonatal care costs of multimillion euros. In spite of that, the commercial market for this clinical indication is rather limited, which may be also related to high liability. Consequently, with only a few exceptions, preterm labor is not in the orbit of great interest of the pharmaceutical industry. Coordinated effort of research community may bring the change and help required to reduce the influence of this multifactorial syndrome on society. Between the novel techniques that are being explored in a SAFE (The Special Non-Invasive Advances in Fetal and Neonatal Evaluation Network) group, there are new research models of preterm labor as well as novel methodology of analysis of biological signals. In this article, we briefly describe new clinical and nonclinical human models of preterm labor as well as summarize some novel methods of data processing and analysis that may be used in the context of preterm labor.

Steroid hormone control of myometrial contractility and parturition

The precise temporal control of uterine contractility is essential for the success of pregnancy. For most of pregnancy, progesterone acting through genomic and non-genomic mechanisms promotes myometrial relaxation. At parturition the relaxatory actions of progesterone are nullified and the combined stimulatory actions of estrogens and other factors such as myometrial distention and immune/inflammatory cytokines, transform the myometrium to a highly contractile and excitable state leading to labor and delivery. This review addresses current understanding of how progesterone and estrogens affect the contractility of the pregnancy myometrium and how their actions are coordinated and controlled as part of the parturition cascade.

Increased recurrence of preterm delivery with early cessation of 17-alpha-hydroxyprogesterone caproate

OBJECTIVE

The purpose of this study was to identify the effect of early cessation of 17-alpha-hydroxyprogesterone caproate (17P) on the incidence of spontaneous recurrent preterm delivery (PTD).

STUDY DESIGN

Retrospective analysis of data from women who were enrolled for outpatient 17P administration between January 2004 and May 2006 included women with previous PTD and current singleton pregnancy who were beginning weekly 17P injections (250 mg intramuscularly) at 16-20.9 weeks. The study group was comprised of patients who were electively terminating 17P at <32.0 weeks and who delivered >10 days from the last injection. The control group consisted of patients who received weekly 17P injections until PTD or 36.9 weeks of gestation. The primary study outcome was the rate of recurrent spontaneous PTD.

RESULTS

Study group patients were significantly more likely to have spontaneous recurrent PTD at <37 weeks of gestation (48.1% vs 33.3%; P = .011), at <35 weeks of gestation (30.9% vs 14.0%; P < .001), and at <32 weeks of gestation (16.0% vs 7.0%; P = .020).

CONCLUSION

Early cessation of 17P treatment is associated with an increased risk for spontaneous recurrent PTD.