Recurrence Of Preterm Birth Research Articles

Preterm birth recurrence after spontaneous preterm birth between 16-28 weeks: a national cohort study

Preterm birth recurrence after spontaneous preterm birth between 16-28 weeks: a national cohort study

Trends and risk of recurrent preterm birth in pregnancy cohorts in rural Bangladesh, 1990–2019

IntroductionA history of preterm birth reportedly increases the risk of subsequent preterm birth. This association has primarily been studied in high-income countries and not in low-income settings in transition with...

Patterns of recurrent preterm birth in Western Australia: A 36-year state-wide population-based study.

It is known that a previous preterm birth increases the risk of a subsequent preterm birth, but a limited number of studies have examined this beyond two consecutive pregnancies. This study aimed to assess the risk and patterns of (recurrent) preterm birth up to the fourth pregnancy. We used Western Australian routinely linked population health datasets to identify women who had two or more consecutive singleton births (≥20weeks gestation) from 1980 to 2015. A log-binomial model was used to calculate risk ratios (RRs) and 95% confidence interval (CIs) for preterm birth risk in the third and fourth deliveries by the combined outcomes of previous pregnancies. We analysed 255435 women with 651726 births. About 7% of women had a preterm birth in the first delivery, and the rate of continuous preterm birth recurrence was 22.9% (second), 44.9% (third) and 58.5% (fourth) deliveries. The risk of preterm birth at the third delivery was highest for women with two prior indicated preterm births (RR 12.5, 95% CI: 11.3, 13.9) and for those whose first pregnancy was 32-36weeks gestation, and second pregnancy was less than 32weeks gestation (RR 11.8, 95% CI: 10.3, 13.5). There were similar findings for the second and fourth deliveries. Our findings demonstrate that women with any prior preterm birth were at greater risk of preterm birth in subsequent pregnancies compared with women with only term births, and the risk increased with shorter gestational length, and the number of previous preterm deliveries, especially sequential ones.

Recurrence of preterm births: A population-based linkage with 3.5 million live births from the CIDACS Birth Cohort.

ObjectiveTo investigate the recurrence of preterm birth (PTB) among the poorest half of the Brazilian population.MethodsWe conducted a population-based retrospective study in Brazil with the live births of multiparous women extracted from the CIDACS Birth Cohort between 2001 and 2015. We used multivariate logistic regression to estimate the odds of recurrent PTB in second and third births.ResultsA total of 3,528,050 live births from 1,764,025 multiparous women were analyzed. The adjusted odds for the occurrence of a PTB given a previous PTB was 2.58 (95% CI 2.53-2.62). Lower gestational age increased the odds of a subsequent PTB [(aOR <28 weeks 3.61, 95% CI 3.41-3.83), (aOR 28 to 31 weeks 3.34, 95% CI 3.19-3.49), (aOR 32 to 36 weeks 2.42, 95% CI 2.38-2.47)]. Women who had two previous PTBs were at high risk of having a third (aOR 4,98 IC 95% 4.70-5.27). Recurrence of a PTB was more likely when the inter-birth interval was less than 12 months.ConclusionsIn Brazil, a middle-income country, women with a previous PTB had an increased risk of a subsequent one. This association was affected by gestational age, the number of PTBs, severity of previous PTBs, and a short interval between births.

Vaginal bacterial load in the second trimester is associated with early preterm birth recurrence: a nested case-control study.

To assess the association between vaginal microbiome (VMB) composition and recurrent early spontaneous preterm birth (sPTB)/preterm prelabour rupture of membranes (PPROM). Nested case-control study. UK tertiary referral hospital. High-risk women with previous sPTB/PPROM <34+0 weeks' gestation who had a recurrence (n = 22) or delivered at ≥37+0 weeks without PPROM (n = 87). Vaginal swabs collected between 15 and 22 weeks' gestation were analysed by 16S rRNA gene sequencing and 16S quantitative PCR. Recurrent early sPTB/PPROM. Of the 109 high-risk women, 28 had anaerobic vaginal dysbiosis, with the remainder dominated by lactobacilli (Lactobacillus iners 36/109, Lactobacillus crispatus 23/109, or other 22/109). VMB type and diversity were not associated with recurrence. Women with a recurrence, compared to those without, had a higher median vaginal bacterial load (8.64 versus 7.89 log10 cells/mcl, adjusted odds ratio [aOR] 1.90, 95% CI 1.01-3.56, P = 0.047) and estimated Lactobacillus concentration (8.59 versus 7.48 log10 cells/mcl, aOR 2.35, (95% CI 1.20-4.61, P = 0.013). A higher recurrence risk was associated with higher median bacterial loads for each VMB type after stratification, although statistical significance was reached only for L. iners domination (aOR 3.44, 95% CI 1.06-11.15, P = 0.040). Women with anaerobic dysbiosis or L. iners domination had a higher median vaginal bacterial load than women with a VMB dominated by L. crispatus or other lactobacilli (8.54, 7.96, 7.63, and 7.53 log10 cells/mcl, respectively). Vaginal bacterial load is associated with early sPTB/PPROM recurrence. Domination by lactobacilli other than L. iners may protect women from developing high bacterial loads. Future PTB studies should quantify vaginal bacteria and yeasts. Increased vaginal bacterial load in the second trimester may be associated with recurrent early spontaneous preterm birth.

Recurrence rate of preterm birth and associated factors among women who delivered at Kilimanjaro Christian Medical Centre in Northern Tanzania: A registry based cohort study.

Preterm birth is a public health problem particularly in low- and middle-income countries especially in sub-Saharan Africa. It is associated with infant morbidity and mortality. Survivor of preterm suffers long term health consequences such as respiratory, hearing and visual problems as well as delivering preterm infants. Preterm birth also tends to recur in subsequent pregnancies. Little is known about recurrent rate of preterm birth and associated factors in Tanzania. This study aimed to determine the recurrence rate of preterm birth and associated factors among women who delivered at Kilimanjaro Christian Medical Centre (KCMC), in Northern Tanzania. A historic cohort study was designed using maternally-linked data from KCMC medical birth registry. Women who delivered 2 or more singletons were included. A total of 5,946 deliveries were analysed. Recurrence of preterm birth and associated risk factors were estimated using multivariable log-binomial regression model with robust standard error to account for repeated births from the same mother. Overall recurrent rate of preterm birth was 24.4%. The recurrence of early preterm birth was higher compared to late preterm birth (26.2% vs. 24.2%). Similar pattern of recurrence was observed for spontaneous and medically indicated preterm birth (13.5% vs. 10.9%, respectively). Previous preterm birth (RR;1.85, 95% CI: 1.49, 2.31), preeclampsia (RR;1.46, 95% CI: 1.07, 2.00), long inter-pregnancy interval (RR;1.22, 95% CI: 1.01, 1.49) and clinical subtypes (RR = 1.37, 95% CI: 1.00, 1.86) were important predictors for recurrent preterm birth. Recurrence of preterm birth remains higher in this population. The rate of preterm recurrence was dependent of gestational age and sub-clinical subtype. Other factors which were associated with recurrence of preterm birth were previous preterm birth, preeclampsia and long inter-pregnancy interval. Early identification of high risk women during prenatal period is warranted.

Retrospective study of the recurrence risk of preterm birth in Japan

Background A history of preterm birth is a risk factor for preterm birth in a future pregnancy, and there are some reports of prevention methods, such as the administration of progesterone. However, the rate of recurrence of preterm birth in Japan has not been clarified, and there is no data for judging whether these preventive methods are effective. Objective To clarify the risk of recurrence of preterm birth and preterm prelabor rupture of membranes (pPROM) in Japan. Materials and methods A retrospective study was conducted using the perinatal registration database of the Japan Obstetrics and Gynecology Society for the Perinatal Center from 2014 to 2016. There were 704,418 subjects, of which 190,990 were excluded those with unknown maternal information, those under the age of 20 years, those with perinatal disease related to preterm birth, and first-time mothers. Results Logistic model unavailable and multivariate analysis were performed. An analysis of the preterm birth history indicated the risk of preterm birth in the current pregnancy, and the odds ratio for preterm birth recurrence once, twice, and three times or more was 3.3, 6.6, and 7.8, respectively. As a secondary analysis, we analyzed whether the history of pPROM is a risk factor of recurrence of pPROM and found a significant association with an odds ratio of 3.4. Conclusion Having a preterm birth history increases the risk of recurrence of preterm birth, and the risk of recurrent preterm birth increases as the number of preterm births increases. Although this report is intended for high-risk pregnancies wherein the rate of preterm birth is high, as previously reported, our data indicate that in Japan, preterm birth is a risk factor of recurrent preterm birth.

Recurrence risk of preterm births: a retrospective Indian study

Preterm birth (PTB) is the leading cause of neonatal deaths and India is the biggest contributor to the global burden of PTBs. This study aimed to determine the risk of recurrence of PTBs and factors associated with recurrence among mothers delivered at a tertiary care perinatal centre in India. This retrospective study comprised women who had delivered singleton preterm babies (24–37 weeks of gestation and weighing ≥500 g) in 2009 and 2010, and had subsequent deliveries beyond 24 weeks of gestation by the end of March 2016. Preterm births were stratified as spontaneous and those with an indication for delivery. Information on demographic data and maternal and neonatal outcomes was accessed from the case records or enquired over telephone. Among 291 eligible women, the recurrence rate of PTB was 31.6%; 29.1% for prior spontaneous and 34.0% for indicated preterm deliveries. This recurrence risk is similar to that in the western populations. In 75.0% of the cases, the type of recurrent PTB corresponded to the index PTB. Preeclampsia (PE) was significantly associated with recurrence (OR 7.10; 95% CI: 3.33, 15.11; p < .001); thus, prevention of PE is a key component in the prevention of PTB. Impact Statement What is already known on this subject? Preventing preterm birth (PTB) remains a challenge because the causes of PTBs are numerous, complex and poorly understood. Spontaneous PTB before 34 weeks of gestation is a strong predictor of subsequent spontaneous PTB. Spontaneous PTB is not only associated with increased recurrence of spontaneous but also medically indicated PTB and vice versa. Risk factors may vary by the clinical subtype of the most recent PTB. What the results of this study add? Despite the highest reported number of PTBs, there are no data on recurrence from India. This study reveals that the recurrence rate of PTBs in an Indian population appears to mirror the rates in the developed nations and preeclampsia (PE) is strongly associated with recurrence. What the implications are of these findings for clinical practice and/or future research? The results of this study are useful for counselling women who had previous PTBs regarding their future obstetric outcomes. Focussed research on prediction and prevention of PE is an essential element in the algorithm for prevention of PTBs.

Is there a role for placental histopathology in predicting the recurrence of preterm birth?

Spontaneous preterm birth (sPTB) is a major cause of neonatal morbidity and mortality with a relatively high rate to recurrence. Our aim was to study the role of placental histopathology in predicting recurrence of sPTB. We conducted a retrospective cohort study. The medical records and placental pathologic reports of all women with sPTB (gestational age 230/7-366/7weeks), during 2008-2015, were reviewed. Only women who had a subsequent delivery were included. Multiple pregnancies and women with known uterine anomalies were excluded. Placental histopathology lesions were classified into maternal and fetal vascular malperfusion lesions, acute maternal and fetal inflammatory responses lesions, and chronic inflammatory lesions. Placental lesions were compared between patients with and without recurrent sPTB on their subsequent pregnancies. Maternal characteristics, gestational age, birthweight, and the rate of preterm rupture of membrane at index delivery were similar between the recurrent sPTB (n = 72) and the non-recurrent sPTB (n = 167) groups. The incidence of placental vascular malperfusion lesions, or inflammatory lesions did not differ between the study groups. However, on multivariate logistic regression analysis, the presence of only acute inflammatory response lesions was associated with recurrence of early sPTB ( < 34weeks) (adjusted OR 3.16; 95% CI 1.22-8.18). The presence of isolated placental acute maternal or fetal inflammatory response in index sPTB may be associated with recurrence of early sPTB.

Follow-Up of Asymptomatic High-Risk Patients with Normal Cervical Length to Predict Recurrence of Preterm Birth

Background: A midtrimester cervical length (CL) <25 mm is associated with spontaneous preterm birth (sPTB). However, as CL ≥25 mm is not enough to exclude recurrence in high-risk patients, follow-up CL measurement later in pregnancy has been proposed. Objectives: To evaluate whether CL measurement at 26±1 weeks in asymptomatic high-risk patients improves the prediction of sPTB recurrence. Methods: A retrospective cohort of high-risk women because of previous sPTB was analyzed. Patients with a CL ≥25 mm at 20±1 weeks and subsequent CL measurement at 26±1 weeks were included. The exclusion criteria were incomplete follow-up, any treatment before CL assessments, and medically indicated preterm birth. The association and predictive performance of CL at 26±1 weeks for sPTB was studied. Results: Of 131 patients with a CL measurement at 26±1 weeks, 19 and 4.6% presented sPTB before 37 and 34 weeks, respectively. The rate of sPTB before 37 weeks was higher in women with a CL <25 mm (37.5 vs. 16.5%, RR 2.3 [1.07–4.8], p = 0.045), although the detection rate of CL at 26±1 weeks to predict sPTB before 37 weeks was 24% (95% CI 10–46%). The performance did not improve regardless of the selected cutoff. Conclusions: In asymptomatic high-risk patients, CL <25 mm at 26±1 weeks is associated with higher risk of sPTB. However, the prediction of recurrence by CL was low and did not improve, regardless of the selected cutoff.

Maternal race and intergenerational preterm birth recurrence

Preterm birth is a complex disorder with a heritable genetic component. Studies of primarily White women born preterm show that they have an increased risk of subsequently delivering preterm. This risk of intergenerational preterm birth is poorly defined among Black women. Our objective was to evaluate and compare intergenerational preterm birth risk among non-Hispanic Black and non-Hispanic White mothers. This was a population-based retrospective cohort study, using the Virginia Intergenerational Linked Birth File. All non-Hispanic Black and non-Hispanic White mothers born in Virginia 1960 through 1996 who delivered their first live-born, nonanomalous, singleton infant ≥20 weeks from 2005 through 2009 were included. We assessed the overall gestational age distribution between non-Hispanic Black and White mothers born term and preterm (<37 weeks) and their infants born term and preterm (<37 weeks) using Cox regression and Kaplan-Meier survivor functions. Mothers were grouped by maternal gestational age at delivery (term, ≥37 completed weeks; late preterm birth, 34-36 weeks; and early preterm birth, <34 weeks). The primary outcomes were: (1) preterm birth among all eligible births; and (2) suspected spontaneous preterm birth among births to women with medical complications (eg, diabetes, hypertension, preeclampsia and thus higher risk for a medically indicated preterm birth). Multivariable logistic regression was used to estimate odds of preterm birth and spontaneous preterm birth by maternal race and maternal gestational age after adjusting for confounders including maternal education, maternal age, smoking, drug/alcohol use, and infant gender. Of 173,822 deliveries captured in the intergenerational birth cohort, 71,676 (41.2%) women met inclusion criteria for this study. Of the entire cohort, 30.0% (n= 21,467) were non-Hispanic Black and 70.0% were non-Hispanic White mothers. Compared to non-Hispanic White mothers, non-Hispanic Black mothers were more likely to have been born late preterm (6.8% vs 3.7%) or early preterm (2.8 vs 1.0%), P < .001. Non-Hispanic White mothers who were born(early or late) preterm were not at an increased risk of early or late preterm delivery compared to non-Hispanic White mothers born term. The risk of early preterm birth was most pronounced for Black mothers who were born early preterm (adjusted odds ratio, 3.26; 95% confidence interval, 1.77-6.02) compared to non-Hispanic White mothers. We found an intergenerational effect of preterm birth among non-Hispanic Black mothers but not non-Hispanic White mothers. Black mothers born <34 weeks carry the highest risk of delivering their first child very preterm. Future studies should elucidate the underlying pathways leading to this racial disparity.

Maternal race and intergenerational preterm birth recurrence

Maternal race and intergenerational preterm birth recurrence

Recurrence of Preterm Birth and Early Term Birth.

To examine recurrent preterm birth and early term birth in women's initial and immediately subsequent pregnancies. This retrospective cohort study included 163,889 women who delivered their first and second liveborn singleton neonates between 20 and 44 weeks of gestation in California from 2005 through 2011. Data from hospital discharge records and birth certificates were used for analyses. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using logistic regression models adjusted for risk factors. Shorter gestational duration in the first pregnancy increased the risk of subsequent preterm birth (both early, before 32 weeks of gestation, and later, from 32 to 36 weeks of gestation) as well as early term birth (37-38 weeks of gestation). Compared with women with a prior term birth, women with a prior early preterm birth (before 32 weeks of gestation) were at the highest risk for a subsequent early preterm birth (58/935 [6.2%] compared with 367/118,505 [0.3%], adjusted OR 23.3, 95% CI 17.2-31.7). Women with a prior early term birth had more than a twofold increased risk for subsequent preterm birth (before 32 weeks of gestation: 171/36,017 [0.5%], adjusted OR 2.0, 95% CI 1.6-2.3; from 32 to 36 weeks of gestation: 2,086/36,017 [6.8%], adjusted OR 3.0, 95% CI 2.9-3.2) or early term birth (13,582/36,017 [37.7%], adjusted OR 2.2, 95% CI 2.2-2.3). Both preterm birth and early term birth are associated with these outcomes in a subsequent pregnancy. Increased clinical attention and research efforts may benefit from a focus on women with a prior early term birth as well as those with prior preterm birth.

Targeted Sequencing and Meta-Analysis of Preterm Birth.

Understanding the genetic contribution(s) to the risk of preterm birth may lead to the development of interventions for treatment, prediction and prevention. Twin studies suggest heritability of preterm birth is 36–40%. Large epidemiological analyses support a primary maternal origin for recurrence of preterm birth, with little effect of paternal or fetal genetic factors. We exploited an “extreme phenotype” of preterm birth to leverage the likelihood of genetic discovery. We compared variants identified by targeted sequencing of women with 2–3 generations of preterm birth with term controls without history of preterm birth. We used a meta-genomic, bi-clustering algorithm to identify gene sets coordinately associated with preterm birth. We identified 33 genes including 217 variants from 5 modules that were significantly different between cases and controls. The most frequently identified and connected genes in the exome library were IGF1, ATM and IQGAP2. Likewise, SOS1, RAF1 and AKT3 were most frequent in the haplotype library. Additionally, SERPINB8, AZU1 and WASF3 showed significant differences in abundance of variants in the univariate comparison of cases and controls. The biological processes impacted by these gene sets included: cell motility, migration and locomotion; response to glucocorticoid stimulus; signal transduction; metabolic regulation and control of apoptosis.

Preterm birth in the first pregnancy and risk of neonatal death in the second pregnancy: A propensity score-weighted matching approach

The study purpose was to assess the relationship between various grades of preterm birth (moderate preterm: 33–36 weeks; severe preterm: 27–32 weeks; extreme preterm: ≤ 26 weeks) in the first pregnancy and neonatal mortality (death within 28 days of birth; early: 0–7 days; late: 8–28 days) in the second pregnancy. Using the Missouri maternally-linked dataset (1989–2005), a population-based, retrospective cohort analysis with propensity score-weighted matching was conducted on mothers with two consecutive singleton live births (n = 310,653 women). Women with a prior preterm birth were more likely to subsequently experience neonatal death. The odds increased in a dose-dependent pattern with ascending severity of the preterm event in the first pregnancy (moderate preterm: AOR = 1.32; 95% CI: 1.10–1.60; severe preterm: AOR = 2.62; 95% CI: 2.01–3.41; extreme preterm: AOR = 5.84; 95% CI: 4.28–7.97; p value for trend < 0.001). However, the pathway for the relationship between prior preterm birth and subsequent neonatal mortality may be the recurrence of preterm birth.

Impact of obstetric history on the risk of spontaneous preterm birth in singleton and multiple pregnancies: a systematic review.

Information about the recurrence of spontaneous preterm birth in subsequent twin/singleton pregnancies is scattered. To quantify the risk of recurrence of spontaneous preterm birth in different subtypes of subsequent pregnancies. An electronic literature search in OVID MEDLINE and EMBASE, complemented by PubMed, to find recent studies. Studies comparing the risk of spontaneous preterm birth after a previous preterm and previous term pregnancy. The absolute risk of recurrence with a 95% confidence interval and the absolute risk of preterm birth after a term delivery were calculated. Data from studies were pooled using the Mantel-Haenszel method. We detected 13 relevant studies. The risk of recurrence of preterm birth was significantly increased in all preterm pregnancy subtypes, compared with their term counterparts. Women pregnant with twins after a previous preterm singleton had the highest absolute risk of recurrence (57.0%, 95% CI 51.9-61.9%), and after a previous term singleton their absolute risk was 25% (95% CI 24.3-26.5%). Women pregnant with a singleton after a previous preterm twin pregnancy have an absolute recurrence risk of 10% (95% CI 8.2-12.3%), whereas a singleton pregnancy after delivering a previous twin up to term yields a low absolute risk of only 1.3% (95% CI 0.8-2.2). Women pregnant with a singleton after a previous preterm singleton have an absolute recurrence risk of 20% (95% CI 19.9-20.6). The risk of recurrence of preterm birth is influenced by the singleton/twin order in both pregnancies, and varies between 10% for a singleton after previous preterm twins to 57% for twins after a previous preterm singleton.

Recurrence of preterm birth and perinatal mortality in northern Tanzania: registry-based cohort study.

ObjectivesTo estimate the recurrence risk of preterm delivery and estimate the perinatal mortality in repeated preterm deliveries.MethodsProspective study in Tanzania of 18 176 women who delivered a singleton between 2000 and 2008 at KCMC hospital. The women were followed up to 2010 for consecutive births. A total of 3359 women were identified with a total of 3867 subsequent deliveries in the follow-up period. Recurrence risk of preterm birth and perinatal mortality was estimated using log-binomial regression and adjusted for potential confounders.ResultsFor women with a previous preterm birth, the risk of preterm birth in a subsequent pregnancy was 17%. This recurrence risk was estimated to be 2.7-fold (95% CI: 2.1–3.4) of the risk of women with a previous term birth. The perinatal mortality of babies in a second preterm birth of the same woman was 15%. Babies born at term who had an older sibling that was born preterm had a perinatal mortality of 10%. Babies born at term who had an older sibling who was also born at term had a perinatal mortality of 1.7%.ConclusionPrevious delivery of a preterm infant is a strong predictor of future preterm births in Tanzania. Previous or repeated preterm births increase the risk of perinatal death substantially in the subsequent pregnancy.

514: Recurrence of preterm birth and perinatal mortality in Northern Tanzania: registry-based cohort study

514: Recurrence of preterm birth and perinatal mortality in Northern Tanzania: registry-based cohort study

Is the Accuracy of Prior Preterm Birth History Biased by Delivery Characteristics?

To assess the sensitivity of birth certificates to preterm birth history and determine whether omissions are randomly or systemically biased. Subjects who experienced a preterm birth followed by a subsequent pregnancy were identified in a regional database. The variable "previous preterm birth" was abstracted from birth certificates of the subsequent pregnancy. Clinical characteristics were compared between subjects who were correctly versus incorrectly coded. 713 subjects were identified, of whom 65.5% were correctly coded in their subsequent pregnancy. Compared to correctly coded patients, patients who were not correctly identified tended to have late and non-recurrent preterm births or deliveries that were secondary to maternal or fetal indications. A recurrence of preterm birth in the subsequent pregnancy was also associated with correct coding. The overall sensitivity of birth certificates to preterm birth history is suboptimal. Omissions are not random, and are associated with obstetrical characteristics from both the current and prior deliveries. As a consequence, resulting associations may be flawed.

Maintenance Therapy by Vaginal Progesterone after Threatened Idiopathic Preterm Labor: A Randomized Placebo-Controlled Double-blind Trial

Background Patients with arrested preterm labor (PTL) are at increased risk for recurrence of preterm birth (PTB). Maintenance tocolysis after arrest of acute PTL is of questionable value. The objective of this study was to evaluate the efficacy of 200 mg vaginal progesterone in order to prevent PTB in women with episodes of threatened PTL. Materials and methods This is a randomized double blind clinical trial study.Women with singleton pregnancies between 28-36 weeks of gestation, who were hospitalized for PTL were included. A total of 173 pregnant patients were randomly allocated to receive 200 mg vaginal progesterone suppositories (n=86) or placebo (n=87) daily until the 36th gestational week. The two groups were compared relative to demographic characteristics, incidence of PTB before 34 and 37 weeks, and maternal and neonatal complications. Data were analyzed by chi-square and Fisher’s exact tests. Results Mean latency until delivery in the cases was longer than the control group (23.88 ± 18.01 vs. 16.67 ± 12.9; p=0.004).Treatment with progesterone was not associated with a reduction in the rate of PTB before 34 weeks [cases: 9 (10.8%) vs. controls: 8 (10%)] and 37 weeks [cases: 45 (54.2%) vs. controls: 33 (41.2%)]. Log rank analysis revealed a significant difference for mean time to delivery between the two groups (p=0.028). There were no significant differences for neonatal and maternal complications in the two groups. Conclusion Prophylactic administration of 200 mg vaginal progesterone suppositories after successful tocolysis in patients with threatened idiopathic PTL is associated with a longer latency to delivery, but failed to reduce the rate of PTB (Registeration Number: IRCT138706051096N1).