Prevention of recurrent preterm delivery by 17 alpha-hydroxyprogesterone caproate

Future directions of failed implantation and recurrent miscarriage research

Recurrent implantation failure is today the major reason for women completing several IVF/intracytoplasmic sperm injection attempts without having achieved a child, and is probably also the explanation for many cases of unexplained infertility. Most causes of recurrent miscarriage are still poorly elucidated, but from a theoretical point of view recurrent implantation failure and recurrent miscarriage are suggested to have partly overlapping causes. Recent research has indeed documented that both syndromes can be caused by the same embryonic chromosomal abnormalities and the same maternal endocrine, thrombophilic and immunological disturbances. Consequently, many treatments attempting to normalize these abnormalities have been tested or are currently used in women with both recurrent implantation failure and recurrent miscarriage. However, no treatment for the two syndromes is at the moment sufficiently documented to justify its routine use. In this review, an overview is given regarding present knowledge about causes that may be common for recurrent implantation failure and recurrent miscarriage, and suggestions are put forward for future research that may significantly improve understanding and treatment options for the syndromes.

“Natural” progesterone: information on fetal effects

BACKGROUND

A variety of progestational agents have been used therapeutically and evaluated for adverse effects over the last 50 years. However, progesterone itself has come into use as a therapeutic agent only recently with the development of an orally bioavailable "micronized" preparation.

METHODS

The current review examines progesterone adverse effects as identified in the larger literature on the toxicity of progestational agents and pharmacokinetics.

RESULTS

Progesterone has cytoplasmic and membrane receptors in a variety of reproductive and nonreproductive tissues including the brain and is a potent inhibitor of GnRH. Limited information is available on progesterone receptors and actions in the fetus. Concern about exogenous progestagen effects on fetal reproductive tract development have led to considerable human research over the years, but this literature review demonstrates that contemporary developmental toxicology research on progesterone is lacking.

CONCLUSIONS

Progesterone is a potent, multi-faceted endocrine agent with an expanding therapeutic profile and a minimal scientific database for evaluating safe use during pregnancy.

Pregnancy-induced decrease in the relaxant effect of terbutaline in the late-pregnant rat myometrium: role of G-protein activation and progesterone

The effectiveness of beta2-agonists in preterm delivery is reduced by several factors. The aim of this study was to determine the influence of late pregnancy in the uterus-relaxing effect of terbutaline in the rat in vitro. Rat uterine tissues from late pregnancy (days 15, 18, 20 and 22) were used. In vitro electrical field-stimulation (EFS) was used to evoke contractions. The radioligand-binding technique, reverse transcription-polymerase chain reaction and radioimmunoassay technique were used to determine the beta-adrenergic receptor density and mRNA level and the plasma sex hormone level, respectively. The activated G-protein level of the beta-adrenergic receptors was investigated by a radiolabelled GTP binding assay.EFS-induced contractions were inhibited by terbutaline. This effect decreased towards term with respect to both the EC50 and maximal inhibition values. A drop in plasma progesterone level was also detected. Binding studies revealed an increase in beta-adrenergic receptor number on the last day of pregnancy, which correlated with the change in receptor mRNA level. The G-protein-activating effect of terbutaline decreased continuously between days 15 and 20. Surprisingly, terbutaline decreased the G-protein activation to below the basal level on day 22. However, progesterone pretreatment set back the uterine action of terbutaline, increased the density of the beta2-adrenergic receptors and their mRNA level and increased the G-protein-activating property of terbutaline. These data provide evidence of a pregnancy-induced decrease in activated G-protein level after beta2-agonist stimulation. The decrease in plasma progesterone level has a crucial role in this process. The effects of beta2-adrenergic receptor agonists in tocolytic therapy may possibly be potentiated with progesterone.

Risk of spontaneous preterm birth is associated with common proinflammatory cytokine polymorphisms

BACKGROUND

Preliminary data suggest that common genetic variation in immune response genes can contribute to the risk for spontaneous preterm birth and possibly small-for-gestational age (SGA).

METHODS

We investigated the relationship of polymorphisms in 6 cytokine genes associated with inflammation-interleukin (IL)1alpha, IL1beta, IL2, IL6, tumor necrosis factor (TNF), and lymphotoxin alpha (LTA)-with spontaneous preterm and SGA birth in a nested case-control study drawn from a prospective pregnancy cohort. Women were recruited between 24 and 29 weeks' gestation at the Wake County and University of North Carolina, Chapel Hill obstetric clinics between February 1996 and June 2000. We inferred haplotypes using the EM algorithm and the Bayesian method, PHASE. We then compared haplotype frequency distributions and implemented semi-Bayesian hierarchical logistic regression analyses to obtain odds ratio (OR) estimates and 95% confidence intervals (CIs) for each polymorphism.

RESULTS

Two haplotypes spanning the TNF/LTA genes were associated with increased risk for spontaneous preterm birth in white subjects (for the AGG haplotype, OR = 1.5 [95% CI=0.8-2.6]; for the GAC haplotype, 1.6 [0.9-2.9]). Additionally, carriers of the GAG haplotype were found to have decreased risk of spontaneous preterm birth (0.6; 0.3-1.0). The TNF(-488)A and LTA(IVS1-82)C variants, constituents of the AGG and GAC haplotypes respectively, were also strongly associated with increased risk of spontaneous preterm birth.

CONCLUSIONS

Our results suggest that common genetic variants in proinflammatory cytokine genes could influence the risk for spontaneous preterm birth. Selected TNF/LTA haplotypes were associated with spontaneous preterm birth in both African-American and white subjects. Our data do not support an inflammatory etiology for SGA.

Role of progestogens for the prevention of premature birth

Premature birth represents a major cause of perinatal morbidity and mortality. The short- and long-term sequelae of prematurity have serious consequences for newborn survival and health in later life. In addition, prematurity is a major problem with regard to health expenditure. Despite major progress in obstetrics, perinatology and neonatology, the percentage of premature birth persists and there is even a tendency towards a slight increase. Therefore, besides screening programmes for the detection of vaginal infections, additional therapeutic opportunities must be sought. According to previously published data, vaginal progesterone and intramuscular 17alpha-hydroxyprogesterone caproate should be considered possible treatment options for the prevention of preterm delivery.

Maternal physiology and complications of multiple pregnancy

Approximately 1% to 3% of all pregnancies in the United States are multiple gestations. The vast majority (97-98%) are twin pregnancies. Multiple pregnancies constitute significant risk to both mother and fetuses. Antepartum complications-including preterm labor, preterm premature rupture of the membranes, intrauterine growth restriction, intrauterine fetal demise, gestational diabetes, and preeclampsia-develop in over 80% of multiple pregnancies as compared with approximately 25% of singleton gestations. This article reviews in detail the maternal physiologic adaptations required to support a multiple pregnancy and the maternal complications that develop when these systems fail or are overwhelmed.

Can medroxyprogesterone acetate alter Toll-like receptor expression in a mouse model of intrauterine inflammation?

OBJECTIVE

Activation of the innate immune receptors, Toll-like receptors 2 and 4, are critical for a host inflammatory response to both Gram-positive and Gram-negative organisms. These receptors can initiate and modulate the inflammatory response. Differential regulation of Toll-like receptors may be one of the mechanisms by which intrauterine inflammation signals parturition. Likewise, progestational agents may have the ability to modify this effect. These studies were performed to elucidate the effect of intrauterine inflammation and medroxyprogesterone acetate on Toll-like receptor expression in the uterus, cervix, and placenta in a mouse model of intrauterine inflammation.

STUDY DESIGN

On day 15 of gestation, CD-1 mice were randomized to pretreatment with medroxyprogesterone acetate or vehicle before intrauterine infusion with lipopolysaccharide or sterile saline solution. Six hours after intrauterine infusion, uterine, cervical, and placental tissues were harvested. RNA and protein were extracted. Quantitative polymerase chain reaction was performed for Toll-like receptor 2 and 4 messenger RNA. Western blot analysis was performed with Toll-like receptor 4-specific antibodies.

RESULTS

Intrauterine inflammation up-regulated Toll-like receptor 2 and 4 messenger RNA in uterus, cervix, and placenta. Pretreatment with medroxyprogesterone acetate decreased the lipopolysaccharide-induced up-regulation of Toll-like receptor 2 and 4 messenger RNA in the cervix and placenta. Medroxyprogesterone acetate treatment, in the presence of lipopolysaccharide, was unable to prevent the lipopolysaccharide-induced increase in Toll-like receptor 4 messenger RNA and protein in the uterus. Medroxyprogesterone acetate treatment alone in pregnant mice significantly increased Toll-like receptor 4 messenger RNA expression in the uterus.

CONCLUSION

Intrauterine inflammation has a differential effect on Toll-like receptor 2 and 4 expression. The observed up-regulation of Toll-like receptor 2 in the uterus in response to intrauterine lipopolysaccharide may be a mechanism to augment the inflammatory response and may serve to promote parturition in the setting of inflammation. Consequently, the ability of medroxyprogesterone acetate to suppress lipopolysaccharide-induced up-regulation of Toll-like receptor 2 messenger RNA may be one of the mechanisms by which progestins are able to decrease preterm birth.

Issues in clinical trial design: stopping a trial early and the large and simple trial

During the conduct of a clinical trial, a primary function of the Data Safety and Monitoring Committee is to select the trial conduct and the accumulating data to determine whether the trial should continue or be discontinued earlier than planned. Reasons for early discontinuation of a trial include: evidence of benefit, evidence of harm, and evidence of futility. More than 1 of these elements will often be present. These principles will be illustrated with examples from National Institute of Child Health and Human Development-Maternal-Fetal Medicine Units clinical trials. The "large and simple clinical trial" is a study design rarely undertaken in the United States but commonly used elsewhere. The principles of this type of trial will be introduced and contrasted with those of the "conventional clinical trial."

Research agenda for preterm birth: recommendations from the March of Dimes

Preterm birth (PTB) is a common, serious, and costly health problem affecting nearly 1 in 8 births in the United States. Burdens from PTB are especially severe for the very preterm infant (<32 weeks' gestation), comprising 2% of all US births. Successful prevention needs to include newly focused and adequately funded research, incorporating new technologies and recognition that genetic, environmental, social, and behavioral factors interact in complex pathogeneses and multiple pathways leading to PTB. The March of Dimes Scientific Advisory Committee created this prioritized research agenda, which is aimed at garnering serious attention and expanding resources to make major inroads into the prevention of PTB, targeting six major, overlapping categories: epidemiology, genetics, disparities, inflammation, biologic stress, and clinical trials. Analogous to other common, complex disorders, progress in prevention will require incorporating multipronged risk reduction strategies that are based on sound scientific discovery, as well as on effective translation into clinical care.

Progesterone modulation of inflammatory cytokine production in a fetoplacental artery explant model

OBJECTIVE

The purpose of this study was to determine if progesterone has an effect on fetoplacental artery production of inflammatory cytokines.

STUDY DESIGN

Chorionic plate arteries were dissected from 5 placentas obtained from normal pregnancies after delivery at term. Arteries were incubated in Dulbecco's modified Eagle's medium (DMEM) alone, DMEM and lipopolysaccharide (LPS), DMEM with progesterone (P4), and DMEM with P4 and LPS. Samples of the tissue culture media were collected and evaluated for interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and interleukin-10 (IL-10) by immunoassay.

RESULTS

There was a significant decrease in the production of IL-6 in P4-exposed fetoplacental arteries after LPS stimulation (P < .001). IL-10 and TNF-alpha levels were similar in control and treatment groups after LPS exposure.

CONCLUSION

Pretreating fetoplacental arteries with P4 significantly decreased the production of IL-6 after LPS stimulation without altering the production of TNF-alpha or IL-10.

Does Progesterone Treatment Influence Risk Factors for Recurrent Preterm Delivery?

OBJECTIVE

To examine how demographic and pregnancy characteristics can affect the risk of recurrent preterm delivery and the how the effectiveness of progesterone treatment for prevention alters these relationships.

METHODS

This was a secondary analysis of a randomized trial of 17alpha-hydroxyprogesterone caproate to prevent recurrent preterm delivery in women at risk. Associations of risk factors for preterm delivery (less than 37 completed weeks of gestation) were examined separately for the women in the 17alpha-hydroxyprogesterone caproate (n = 310) and placebo (n = 153) groups.

RESULTS

Univariate analysis found that the number of previous preterm deliveries and whether the penultimate delivery was preterm were significant risk factors for preterm delivery in both the placebo and progesterone groups. High body mass index was protective of preterm birth in the placebo group. Multivariate analysis found progesterone treatment to cancel the risk of more than 1 previous preterm delivery, but not the risk associated with the penultimate pregnancy delivered preterm. Obesity was associated with lower risk for preterm delivery in the placebo group but not in the women treated with progesterone.

CONCLUSION

The use of 17alpha-hydroxyprogesterone caproate in women with a previous preterm delivery reduces the overall risk of preterm delivery and changes the epidemiology of risk factors for recurrent preterm delivery. In particular, these data suggest that 17alpha-hydroxyprogesterone caproate reduces the risk of a history of more than 1 preterm delivery.

LEVEL OF EVIDENCE

I.

Progesterone for prevention of recurrent preterm birth: impact of gestational age at previous delivery

OBJECTIVE

Preterm birth occurs in 1 of 8 pregnancies and may result in significant morbidity and mortality. 17-alpha hydroxyprogesterone caproate (17-OHP caproate) has been found to be efficacious in reducing the risk of subsequent preterm delivery in women who have had a previous spontaneous preterm birth (sPTB). This analysis was undertaken to evaluate if 17-OHP caproate therapy works preferentially depending on the gestational age at previous spontaneous delivery. We hypothesized that treatment with 17-OHP caproate is more effective in prolonging pregnancy depending on the gestational age of the earliest previous preterm birth (20-27.9, 28-33.9 vs 34-36.9 weeks).

STUDY DESIGN

This was a secondary analysis of 459 women with a previous sPTB enrolled in a randomized controlled trial evaluating 17-OHP caproate versus placebo. Effectiveness of 17-OHP caproate for pregnancy prolongation was evaluated based on gestational age at earliest previous delivery according to clinically relevant groupings (20-27.9, 28-33.9, and 34-36.9 weeks). Statistical analysis included the chi-square, Fisher exact, and Kruskal-Wallis tests, logistic regression, and survival analysis using proportional hazards.

RESULTS

Gestational age at earliest previous delivery was similar between women treated with 17-OHP caproate or placebo (P = .1). Women with earliest delivery at 20 to 27.9 weeks and at 28 to 33.9 weeks delivered at significantly more advanced gestational age if treated with 17-OHP caproate than with placebo (median 37.3 vs 35.4 weeks, P = .046 and 38.0 vs 36.7 weeks, P = .004, respectively) and were less likely to deliver <37 weeks (42% vs 63%, P = .026 and 34% vs 56%, P = .005, respectively). Those with earliest delivery at 34 to 36.9 weeks were not significantly different between 17-OHP caproate or control.

CONCLUSION

17-OHP caproate therapy given to prevent recurrent PTB is associated with a prolongation of pregnancy overall, and especially for women with a previous spontaneous PTB at <34 weeks.

Trends in twin preterm birth subtypes in the United States, 1989 through 2000: impact on perinatal mortality

OBJECTIVE

We examined trends in twin preterm birth <37 weeks following ruptured membranes (ROM), medically indicated preterm birth, and preterm birth following spontaneous onset of labor (PTL). We further examined whether the changes in preterm birth subtypes were associated with trends in twin perinatal mortality.

STUDY DESIGN

We carried out a retrospective cohort study of 1,172,405 twin live births and stillbirths delivered in the US between 1989 and 2000. Trends in preterm birth subtypes and perinatal mortality (stillbirths at > or = 22 weeks plus neonatal deaths within 28 days) were examined through ecological logistic regression models after adjusting for confounders.

RESULTS

Twin preterm birth among whites increased from 46.6% in 1989 to 1990 to 56.7% in 1999 to 2000, and from 56.1% to 61.0% among blacks over the same period. Medically indicated preterm birth increased by 50% (95% CI 49-52) among whites, and by 33% (95% CI 29-36) among blacks. PTL increased by 24% among whites, but remained fairly unchanged among blacks between the two periods. Preterm birth following ROM also did not change between the 2 periods among whites, but declined by 7% among blacks. Perinatal mortality among twin births declined by 41% (95% CI 38-44) among whites, and by 37% (95% CI 32-42) among blacks between 1989 and 1990 and 1999 and 2000. This mortality decline was most closely associated with the increase in medically indicated preterm birth among whites, and with the decrease in preterm birth following ROM among blacks.

CONCLUSION

Temporal trends in twin preterm birth varied substantially based on underlying subtypes and race. The increase in medically indicated preterm birth is associated with a large reduction in perinatal mortality.

Preterm Labor in Twins and High-Order Multiples

Preterm labor (PTL) is common in multiple gestations. Management of patients includes attempts at prevention of PTL, acute tocolysis when PTL is diagnosed, and long-term maintenance tocolysis. Clinical therapeutics should be aggressively directed at minimizing the background uterine contractions to reduce the incidence of PTL and to provide a greater chance of suppressing PTL allowing delivery at the ideal gestational age.

Rates of recurrent preterm birth by obstetrical history and cervical length

OBJECTIVE

This study was undertaken to determine rates of recurrent preterm birth according to number of prior preterm births, 1 versus 2 or more and cervical length by endovaginal ultrasound at 22(0) to 24(6) weeks, less than 25 mm versus more than 25 mm.

STUDY DESIGN

We retrospectively analyzed data from charts of women with prior spontaneous preterm birth seen in a Prematurity Prevention Clinic from 1998 through 2004. Women with a history of 1 or more spontaneous preterm births (18(0)-36(6) weeks) were included. Women with multiple gestations, uterine anomalies, and prior cervical surgery were excluded. Transvaginal sonography was used to evaluate each woman's cervical length at 22(0) to 24(6) weeks. Cerclage, bed rest, tocolysis, and steroids were used when clinically appropriate. Primary outcome was gestational age at delivery less than 32 and less than 35 weeks. Data were analyzed according to number of prior preterm births (1 vs > or = 2) and sonographic cervical length at 22(0) to 24(6) weeks (<25 mm vs > or = 25 mm).

RESULTS

A total of 188 eligible women were evaluated. Median gestational age of earliest preterm birth was 26.3 weeks. Of the total 188, 118 (62.8%) women had 1 prior and 70 (37.2%) had 2 or more preterm births. Thirty-eight (20.2%) of the women had a cervical length less than 25 mm and 150 (79.8%) had a cervical length 25 mm or greater. A higher percentage of women with a cervical length less than 25 mm and 2 or more preterm births delivered less than 32 weeks compared with women with 1 prior preterm birth, although this did not reach statistical significance (21.5% vs 12.5%, P = .47). Rates of delivery less than 35 weeks in women with a cervical length less than 25 mm were similar in those with a history of 1 and 2 or more preterm births. Women who had 2 or more prior preterm births were analyzed separately to identify if a cervical length greater than 30 mm or greater than 35 mm could be reassuring for decreasing the risk of recurrent preterm birth.

CONCLUSION

Rates of preterm birth less than 32 and less than 35 weeks were similar in women whose cervical length was less than 25 mm at 22(0) to 24(6) weeks, regardless of number of prior preterm births. Women with 2 prior preterm births and a cervix greater than 35 mm were at low risk for subsequent preterm birth less than 35 weeks.

Plasma CRH measurement at 16 to 20 weeks' gestation does not predict preterm delivery in women at high-risk for preterm delivery

OBJECTIVE

The purpose of this study was to examine the utility of a single second-trimester plasma corticotropin-releasing hormone measurement as a marker for preterm delivery in women at high risk for preterm delivery.

STUDY DESIGN

This is an analysis of data from a multicenter placebo-controlled trial designed to evaluate the role of 17 alpha hydroxyprogesterone caproate (17P) in the prevention of recurrent preterm birth. Women with a documented history of a previous spontaneous preterm birth at <37 weeks were enrolled (16-20 wks) and randomly assigned in a 2 to 1 ratio to weekly injections of 17P or matching placebo. Blood was collected before treatment in 170 patients (113 assigned 17P and 57 placebo) who were enrolled at 11 of the 19 centers. Plasma levels of corticotropin-releasing hormone were compared between those who delivered preterm and those delivering at term. Data were analyzed using the Wilcoxon rank-sum test.

RESULTS

The overall rates of preterm birth in this cohort of 170 patients were 35.9% at <37 weeks (31.9% progesterone, 43.9% placebo), and 19.4% at <35 weeks (18.6% vs 21.1%). The median levels of corticotropin-releasing hormone were similar between those delivering at <37 weeks and those delivering > or = 37 weeks (0.39 ng/mL vs 0.37 ng/mL, P = .08). In addition, there were no differences in corticotropin-releasing hormone levels among those who delivered at <35 weeks or > or = 35 weeks (0.36 vs 0.38, P = .90). Moreover, there were no differences in corticotropin-releasing hormone levels among those in the placebo group who delivered at <37 or > or = 37 weeks (0.40 vs 0.41, P = .72) and at <35 or > or = 35 weeks (P = .64).

CONCLUSION

A single measurement of corticotropin-releasing hormone at 16 to 20 weeks' gestation is not a good biomarker for recurrent preterm delivery in patients at high risk for this complication.

The molecular pathophysiology of bacterially induced preterm labor: insights from the murine model

Premature delivery, the most important problem in obstetrics in developed countries, continues to vex clinicians and researchers. Despite decades of investigation, the pathophysiology of premature labor is incompletely understood, and therapies or preventive strategies tailored to each of the many potential causes do not exist. The present review addresses one cause of prematurity, namely, intrauterine bacterial infection. Given the vastness of the literature for even this single etiology, we focus on the mouse as a model organism from which much can be learned about mammalian parturition. The underpinnings of bacterially induced labor are believed to involve a signaling cascade that begins with recognition of offending pathogens by cell-surface receptors (toll-like receptors). This cascade then operates through multiple branching and redundant pathways to bring about the changes within the gestational compartment that produce cervical ripening, labor, and ultimately delivery. The major challenge facing researchers is to understand the levels of complexity in the host response, so that prevention and treatment strategies may be sufficiently focused to minimize unwanted side effects, yet sufficiently broad to be effective. Given the complexity of the problem, this understanding can be aided by efficient model systems, of which one in vivo example is the mouse, an organism that shares with humans many similarities in the biochemical and molecular aspects of inflammation-induced preterm labor. We propose that tools with the power to assess simultaneously the myriad elements of the hypothesized signaling cascade (ie, genomic and proteomic technologies) are important components of the solution to the puzzle of parturition.

Treatment strategies for mares with placentitis

Equine placentitis, and resultant preterm labor, are important sources of fetal and neonatal loss. The primary cause of equine placentitis is infection of the placenta with Streptococcus equi subspecies zooepidemicus, which ascends through the caudal reproductive tract. Current treatment protocols for mares affected with placentitis are empirical. This paper reviews treatment approaches for resolving placentitis and preterm labor in both equine and non-equine species. Specific therapies reviewed include antimicrobial, anti-inflammatory, tocolytic, and progestin agents.

5β-Dihydroprogesterone and steroid 5β–reductase decrease in association with human parturition at term

The role of progesterone withdrawal in human parturition continues to provoke controversy. One possible mechanism by which functional progesterone withdrawal may be achieved is by a decrease in the circulating concentration of its bioactive metabolites. The progesterone metabolite 5beta-dihydroprogesterone (5betaDHP) has been shown to be a potent tocolytic in vitro. We quantified plasma concentrations of 5betaDHP in association with the onset of spontaneous labour in women at term and steroid 5beta-reductase mRNA expression in placenta, myometrium, chorion and amnion in relation to parturition, using real time RT-PCR. Serial blood samples were obtained from patients late in pregnancy, before term labour, during term labour and within the first 24 h postpartum. Following organic solvent extraction, steroids including 5betaDHP were separated by high-performance liquid chromatography (HPLC) and then quantified by radioimmunoassay (RIA). 5betaDHP concentration decreased two-fold (P = 0.00001, n = 25) from 0.317 +/- 0.039 nmol/ml to 0.178 +/- 0.017 nmol/ml in association with active labour. Tissue 5beta-reductase mRNA-relative abundance was determined in placenta, myometrium, chorion and amnion obtained from labouring and non-labouring women. In placenta and myometrium, relative expression decreased significantly in association with labour, by about two-fold and 10-fold, respectively. These data are consistent with a possible role for 5betaDHP in the onset of spontaneous human labour. Further studies exploring this hitherto unrecognized endocrinological pathway are indicated.

Inflammatory aetiology of human myometrial activation tested using directed graphs

There are three main hypotheses for the activation of the human uterus at labour: functional progesterone withdrawal, inflammatory stimulation, and oxytocin receptor activation. To test these alternatives we have taken information and data from the literature to develop causal pathway models for the activation of human myometrium. The data provided quantitative RT-PCR results on key genes from samples taken before and during labour. Principal component analysis showed that pre-labour samples form a homogenous group compared to those during labour. We therefore modelled the alternative causal pathways in non-labouring samples using directed graphs and statistically compared the likelihood of the different models using structural equations and D-separation approaches. Using the computer program LISREL, inflammatory activation as a primary event was highly consistent with the data (p = 0.925), progesterone withdrawal, as a primary event, is plausible (p = 0.499), yet comparatively unlikely, oxytocin receptor mediated initiation is less compatible with the data (p = 0.091). DGraph, a software program that creates directed graphs, produced similar results (p= 0.684, p= 0.280, and p = 0.04, respectively). This outcome supports an inflammatory aetiology for human labour. Our results demonstrate the value of directed graphs in determining the likelihood of causal relationships in biology in situations where experiments are not possible.

This paper describes how novel computational approaches have been used to test hypotheses for important physiological events when the traditional approaches of animal studies and experiment are not possible. The processes that regulate the onset of human labour are presently unknown, principally because there are no good animal models for human pregnancy and because it is unethical to conduct experiments on pregnant women undergoing labour. However, several hypotheses have been advanced to explain the trigger for labour, including: a functional withdrawal of the hormone progesterone, increased inflammation in the uterus, and increased signalling through the hormone oxytocin. To test these hypotheses the researchers used data on the messenger RNA concentrations of critical variables in samples of uterine muscle taken from 12 women undergoing caesarean section prior to labour and 12 women during labour. Directed graphs for each of the proposed hypotheses were then generated, where the graphs represent the direction of causal influence between different variables. Statistical testing determined how well the graphs of each hypothesis matched the experimental data. The results strongly support an inflammatory origin for the onset of human labour. This approach could be applied to other problems in human biology where the traditional approaches of experiments and animal models are not possible.

Prophylactic oral betamimetics for reducing preterm birth in women with a twin pregnancy

BACKGROUND

Twin pregnancies are associated with a high risk of neonatal mortality and morbidity due to an increased rate of preterm birth. Betamimetics can decrease contraction frequency or delay preterm birth in singleton pregnancies by 24 to 48 hours. The efficacy of oral betamimetics in women with a twin pregnancy is unproven.

OBJECTIVES

To assess the effects of prophylactic oral betamimetics administered to women with twin pregnancies.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group Trials Register (May 2004), CENTRAL (The Cochrane Library, Issue 2, 2004), MEDLINE (January 1966 to May 2004), EMBASE (January 1985 to May 2004), and reference lists.

SELECTION CRITERIA

Randomized controlled trials in twin pregnancies comparing oral betamimetics with placebo or any intervention with the specific aim of preventing preterm birth.

DATA COLLECTION AND ANALYSIS

Standard methods of The Cochrane Collaboration and the Cochrane Pregnancy and Childbirth Group were used. Trials were independently assessed for methodological quality by at least two authors, who extracted data using a data collection form.

MAIN RESULTS

Five trials (344 twin pregnancies) were included. All trials compared oral betamimetics to placebo. Betamimetics reduced the incidence of preterm labour (one trial, 50 twin pregnancies, relative risk (RR) 0.40; 95% confidence interval (CI) 0.19 to 0.86). However, betamimetics did not reduce preterm birth less than 37 weeks' gestation (four trials, 276 twin pregnancies, RR 0.85; 95% CI 0.65 to 1.10) or less than 34 weeks' gestation (one trial, 144 twin pregnancies, RR 0.47; 95% CI 0.15 to 1.50). Mean neonatal birthweight in the betamimetic group was significantly higher than in the placebo group (three trials, 478 neonates, weighted mean difference 111.2 grams; 95% CI 22.2 to 200.2). Nevertheless, there was no evidence of an effect of betamimetics in reduction of low birthweight (two trials, 366 neonates, RR 1.19; 95% CI 0.77 to 1.85) or small-for-gestational age neonates (two trials, 178 neonates, RR 0.92; 95% CI 0.52 to 1.65). Two trials (388 neonates) showed that betamimetics significantly reduced the incidence of respiratory distress syndrome but the difference was not significant when the analysis was adjusted for correlation of babies from twins. Three trials (452 neonates) showed no evidence of an effect of betamimetics in reducing neonatal mortality (RR 0.80; 95% CI 0.35 to 1.82).

AUTHORS' CONCLUSIONS

There is insufficient evidence to support or refute the use of prophylactic oral betamimetics for preventing preterm birth in women with a twin pregnancy.

Hospitalization for Women With Arrested Preterm Labor

OBJECTIVE

To determine whether hospitalization of women with arrested preterm labor has an effect on delivery at 36 weeks or greater when compared with women discharged home.

METHODS

All women with a singleton gestation and a diagnosis of arrested preterm labor with intact membranes between 24 and 33 weeks, 4 days of gestation were randomly assigned to home or hospital management. Upon completion of a dexamethasone course, women assigned to outpatient management were promptly discharged, and women in the inpatient group were advised to continue hospitalization until 34 weeks. Decreased activity was encouraged in both groups. Bed rest was not strictly enforced. The primary outcome was delivery at 36 weeks or greater.

RESULTS

A total of 101 women of a planned 188 were enrolled at the time of an interim analysis. There was no difference in the primary study outcome between the 2 groups and the trial was terminated. Among the hospitalized women, 71% reached 36 weeks or greater, compared with 72% of those discharged home (P = .89). The mean cervical dilatation in hospitalized women was 2.7 +/- 0.5 cm, compared with 2.6 +/- 0.5 cm in women discharged home (P = .16). The overall length of hospital stay for the women allocated to hospitalization was 16 +/- 13 days.

CONCLUSION

Compared with hospitalization, outpatient management of women with arrested preterm labor and intact membranes had no effect on the rate of preterm birth.

LEVEL OF EVIDENCE

I.

Cerclage for Short Cervix on Ultrasonography

OBJECTIVE

Preterm birth is the main cause of perinatal morbidity and mortality. A short cervical length on transvaginal ultrasonography predicts preterm birth. Our aim was to estimate by meta-analysis of randomized trials whether cerclage prevents preterm birth in women with a short cervical length.

DATA SOURCES

MEDLINE, PubMed, EMBASE, and the Cochrane Library were searched with the terms "cerclage," "cervical cerclage," "short cervix," "ultrasound," and "randomized trial." We included randomized trials involving the use of cerclage in women with short cervical length on transvaginal ultrasonography using patient-level data.

TABULATION, INTEGRATION, AND RESULTS

Four properly conducted trials were identified. In the total population, preterm birth at less than 35 weeks of gestation occurred in 29.2% (89/305) of the cerclage group, compared with 34.8% (105/302) of the no-cerclage groups (relative risk [RR] 0.84, 95% confidence interval [CI] 0.67-1.06). There was no significant heterogeneity in the overall analysis (P = .29). There was a significant reduction in preterm birth at less than 35 weeks in the cerclage group compared with the no-cerclage groups in singleton gestations (RR 0.74, 95% CI 0.57-0.96), singleton gestations with prior preterm birth (RR 0.61, 95% CI 0.40-0.92), and singleton gestations with prior second-trimester loss (RR 0.57, 95% CI 0.33-0.99). There was a significant increase in preterm birth at less than 35 weeks in twin gestations (RR 2.15, 95% CI 1.15-4.01).

CONCLUSION

Cerclage does not prevent preterm birth in all women with short cervical length on transvaginal ultrasonography. In the subgroup analysis of singleton gestations with short cervical length, especially those with a prior preterm birth, cerclage may reduce preterm birth, and a well-powered trial should be carried out in this group of patients. In contrast, in twins, cerclage was associated with a significantly higher incidence of preterm birth.

Vaginal radical trachelectomy: A valuable fertility-preserving option in the management of early-stage cervical cancer. A series of 50 pregnancies and review of the literature

OBJECTIVE

To report the obstetrical results following vaginal radical trachelectomy (VRT), a fertility-preserving surgery in the treatment of early-stage cervical cancer.

METHODS

Retrospective review of our first 72 patients treated by a laparoscopic pelvic lymphadenectomy followed by a VRT from October 1991 to October 2003 with regards to their reproductive function.

RESULTS

Patients' median age was 32 years old (21-42) and 53 (74%) were nulligravida. A total of 50 pregnancies occurred in 31 women. The majority (66%) had only one pregnancy, 19% had 2 pregnancies and 16% had 3 pregnancies or more. The rate of first trimester miscarriage was 16%, the rate of second trimester miscarriage was (4%) and 2 women (4%) elected to have pregnancy termination. A total of 36 pregnancies (72%) reached the third trimester. Of those, 3 (8%) ended prematurely at <32 weeks gestation, 5 (14%) delivered between 32 and 36 weeks and 28 (78%) delivered at term (>37 weeks). One newborn died of neonatal sepsis from E. coli infection and one died from cardiac malformation (trisomy-18). Seven patients (10%) had infertility problems: 3 from ovulatory causes of which 2 successfully conceived with IVF, one from endometriosis and low sperm count and 3 from probable cervical cause of which one conceived with IUI. One patient had a twin pregnancy following IVF and elected to have embryo reduction and subsequently delivered at 37 weeks.

CONCLUSION

Based on our experience, the obstetrical results following VRT for early-stage cervical cancer are very encouraging. The majority of women can anticipate to conceive spontaneously and deliver near term.

Trends in preterm birth and perinatal mortality among singletons: United States, 1989 through 2000

OBJECTIVE

Despite the recent increase in preterm birth in the United States, trends in preterm birth subtypes have not been adequately examined. We examined trends in preterm birth among singletons following ruptured membranes, medical indications, and spontaneous preterm birth and evaluated the impact of these trends on perinatal mortality.

METHODS

A population-based, retrospective cohort study comprising 46,375,578 women (16% blacks) who delivered singleton births in the United States, 1989 through 2000, was performed. Rates of preterm birth (< 37 weeks), their subtypes, and associated perinatal mortality (stillbirths at >/= 22 weeks plus neonatal deaths within 28 days), before and after adjustment for potential confounders, were derived from ecological logistic regression models.

RESULTS

Preterm birth rates increased by 14% (95% confidence interval 13-15%) among whites from 8.3% to 9.4% and decreased by 15% (95% confidence interval 14-16%) among blacks from 18.5% to 16.2% between 1989 and 2000. Among whites, preterm birth following ruptured membranes declined by 23%, medically indicated preterm birth increased by 55%, and spontaneous preterm birth increased by 3%. Among blacks, preterm birth following ruptured membranes declined by 37%, medically indicated preterm birth increased by 32%, and spontaneous preterm birth decreased by 27%. The largest decline in perinatal mortality among whites was associated with increases in medically indicated preterm birth, whereas the largest decline in perinatal mortality among blacks was associated with declines in preterm birth following ruptured membranes and spontaneous preterm birth.

CONCLUSION

Temporal trends in preterm birth varied substantially based on underlying subtype and maternal race. The recent increase in medically indicated preterm birth was associated with a favorable reduction in perinatal mortality.

Progesterone supplementation for preventing preterm birth: a systematic review and meta-analysis

AIM

The aim of this study is to assess the role of progesterone in preterm birth prevention.

METHODS

A MEDLINE search (from 1966 to the present; date of last search January 2005) was performed - using the key words progesterone, pregnancy, preterm birth, preterm labor, and randomized, controlled trial - in order to identify randomized, controlled trials in which progesterone (either intramuscular or vaginal administration) was compared with placebo or no treatment. Data were extracted and a meta-analysis was performed.

RESULTS

Seven randomized, controlled trials were identified. Women who received progesterone were statistically significantly less likely to give birth before 37 weeks (seven studies, 1020 women, RR = 0.58, 95% CI = 0.48-0.70), to have an infant with birth weight of < or =2.5 kg (six studies, 872 infants, RR = 0.62, 95% CI = 0.49-0.78), or to have an infant diagnosed with intraventricular hemorrhage (one study, 458 infants, RR = 0.25, 95% CI = 0.08-0.82).

CONCLUSIONS

For progesterone supplementation to be advocated for women at the risk of preterm birth, the prolongation of gestation demonstrated in this meta-analysis must translate into improved infant outcomes, including a reduction in mortality. There is currently insufficient information to allow recommendations regarding the optimal dose, route, and timing of administration of progesterone supplementation.

Mechanisms underlying "functional" progesterone withdrawal at parturition

Progesterone is a major factor maintaining uterine quiescence throughout pregnancy. In most species, peripheral progesterone levels decline before initiation of labor, and treatments that inhibit progesterone synthesis or action cause termination of pregnancy and/or premature deliveries. These findings suggest that progesterone withdrawal is required for activation of myometrial contractions. However, in humans, circulating progesterone levels remain elevated until birth, which leads to the notion that a "functional" progesterone withdrawal occurs before parturition. The apparent loss of progesterone sensitivity at term could be a consequence of several different mechanisms including: (1) the catabolism of progesterone in the uterus into inactive compounds; (2) alterations in progesterone receptor (PR) isoform ratios; (3) changes in cofactor protein levels affecting PR transactivation; and (4) inflammation-induced trans-repression of PR by nuclear factor kappaB. All of these mechanisms are potentially capable of decreasing uterine progesterone responsiveness at term, thus enabling the expression of pathways that originally were blocked by progesterone in early pregnancy. However, the specific uterine genes whose transcription is directly controlled by PR, and thus affected by "functional" progesterone withdrawal, remain to be identified.

Maternal complications of multifetal pregnancy

This article reviews the common maternal complications encountered in multifetal gestations.

Antepartum management of multifetal pregnancies

Correct antepartum management of multifetal gestations is a critical skill for practitioners of obstetrics. This article reviews important issues surrounding these complicated pregnancies while discussing current management options and recommendations. Topics include antepartum surveillance, preterm labor prediction, diagnosis, and management, and special situations unique to multiple gestations, such as twin-twin transfusion syndrome and death of one twin in utero. It is the authors' hope that this article is comprehensive in enhancing the reader's knowledge of these complex pregnancies.

Biochemical markers for the prediction of preterm birth

The prediction of preterm birth may be important (1) to initiate risk specific treatment; (2) to define a population that is at risk in which to study a particular treatment; or (3) to better understand the pathways that lead to preterm birth. Biologic fluids that have been used as sources for tests include serum, plasma, amniotic fluid, urine, vaginal and cervical secretions, saliva, and even periodontal fluid. We discuss the types of substances that are found in body fluids (eg, organisms, cytokines, enzymes, hormones) that have been studied as predictors of preterm birth, the fluids in which they are found, and issues that are related to the timing of the test, the cost, and the ease of fluid collection and processing. We emphasize that a test for any of these substances should not be introduced into clinical practice until the use of the test, which is followed by an appropriate intervention, leads to a reduction in preterm birth.

Comparative longitudinal study of cervical length and induced shortening changes among singleton, twin, and triplet pregnancies

OBJECTIVE

To compare cervical length and induced shortening changes during gestation among singleton, twin, and triplet pregnancies.

STUDY DESIGN

Thirty-two healthy gravidas (12 singleton, 13 twin, and 7 triplet pregnancies) between 17 and 20 weeks' gestation were prospectively enrolled in this longitudinal investigation of cervical length. Serial transperineal cervical length ultrasound assessments were made weekly until 34 weeks' gestation under 3 conditions: 1) supine, 2) supine with the Valsalva maneuver, and 3) standing. Cervical length, internal os diameter, and presence of cervical funneling were assessed under each condition. Multiple regression models were created using generalized estimating equations to predict these measures and accounting for confounding effects from covariates and adjusting for correlations from repeated measurements on each woman.

RESULTS

A total of 1286 cervical sonographic measurements were made. In a multiple linear regression generalized estimating equations model, estimated cervical length was significantly different among singleton, twin, and triplet pregnancies. Overall, changing maternal position from supine to standing resulted in a nonsignificant change (-0.1 +/- 0.4 mm) in cervical length (P = .85). In contrast, measurement of cervical length during the Valsalva maneuver resulted in a significant reduction in cervical length when compared with the cervical length measured in supine (-1.0 +/- 0.3 mm) (P = .0009) and standing positions (-0.9 +/- 0.4) (P = .009). The observed induced shortening changes were similar across gestation, irrespective of singleton, twin, or triplet gestation.

CONCLUSION

Longitudinal cervical length changes differ significantly throughout gestation among singleton, twin, and triplet pregnancies. Cervical length measurements made in a standing position are comparable with those measured while supine, whereas cervical lengths measured during the Valsalva maneuver are significantly shorter than those made in either the supine or standing position.

17 Hydroxyprogesterone for the Prevention of Preterm Delivery

The recent publication of 2 large randomized trials of 17 alpha hydroxyprogesterone caproate (17P) and progesterone suppositories, respectively, for the prevention of premature labor have renewed interest in the use of progesterone to prevent preterm birth. The results of these trials have reinforced the positive results of earlier smaller trials of 17P to prevent preterm delivery. A large body of evidence attests to the lack of teratogenic effects of 17P in pregnancy. Although progesterone is known to have many actions beneficial to the maintenance of pregnancy, the exact mode of action of 17P therapy in preventing preterm labor and delivery is not known. Current evidence supports the use of 17P treatment, begun early in the second trimester of gestation and continued weekly until 36 weeks, for women with a history of a previous spontaneous preterm delivery. At present no evidence exists for the use of 17P to prevent preterm delivery in women with multiple gestation, a short uterine cervix, or other high-risk conditions. The use of 17P or other progestins should not be encouraged for these indications outside of randomized trials. At present no evidence exists for the efficacy of any oral progesterone compound in preventing preterm labor. Four trials reporting the use of a progestational drug in patients with symptoms of preterm labor found no efficacy in prolonging pregnancy, and the use of 17P or other progestational drugs as tocolytic therapy should not be encouraged.

Recent pharmacological advances in the treatment of preterm membrane rupture, labour and delivery

Preterm delivery (before 37 completed weeks of gestation) is the major determinant of infant mortality. In women with a previous preterm birth associated with bacterial vaginosis, prophylactic antibiotics (e.g., metronidazole) reduce the risk of preterm birth and low birth weight. Trichomonas vaginalis increases the risk of preterm delivery, but metronidazole is not beneficial for this and may even be detrimental. Antibiotic use (e.g., erythromycin) prolongs pregnancy in late premature rupture and has health benefits for the neonate. However, antibiotics are probably not useful in preterm labour. Intramuscular 17alpha-progesterone and vaginal progesterone reduce the rate of preterm labour in high-risk pregnancies, including previous spontaneous preterm delivery. Magnesium sulfate, beta2-adrenoceptor agonists and the oxytocin-receptor antagonist, atosiban, are effective in reducing uterine contractions short-term, but there is little evidence that this leads to improved outcomes for the neonate. However, tocolysis with calcium-channel blockers does seem to lead to better outcomes for the neonate. Fetal side effects, such as ductus arteriosus constriction and impaired renal function, are associated with the inhibition of prostaglandin synthesis with indomethacin. New approaches and more effective drugs are required in the treatment of preterm delivery.

Progesterone receptor expression in human decidua and fetal membranes before and after contractions: possible mechanism for functional progesterone withdrawal

In humans, progesterone levels are sustained before the onset of labour. Therefore, the mechanism for parturition that has been proposed for humans is 'functional' progesterone withdrawal. Immunohistochemical staining for the progesterone receptor (PR) was positive in the decidua with a decline after contractions began. Western blot analysis revealed a number of PR isoforms expressed in the decidua, with the PR-B form being dominant. After contractions began, all PR isoforms decreased sharply. PR-B and PR-A decreased by 85.8% +/- 6.7 and 78.2% +/- 7.1, respectively (P < 0.001). Incubation of decidua with Prostaglandin F2alpha 1.0 microg/ml decreased the expression of all forms of PR isoforms. PR-B was reduced by 64% +/- 6.09 (P < 0.01); PR-A was reduced by 77% +/- 5.9 (P < 0.05), while PR-C was reduced by 80% +/- 7.24 (P < 0.05). Progesterone (80 microg/ml) increased the PR-B, PR-C the 45 and 36 kDa isoforms to 150% +/- 7.89, 210% +/- 12.4, 270% +/- 9.7 and 216% +/- 13.5, respectively (P < 0.05). In immunohistochemical studies, the PR was not identified in the amnion or in the chorion, regardless of the presence or absence of contractions. Western blot analysis demonstrated that PR-C (60 kDa) and the 36 kDa isoforms were dominant in the amnion. After contractions began, PR-A decreased significantly by 61.9% +/- 7.1 (P < 0.001).

Sonographic measurement of cervical length in threatened preterm labor in singleton pregnancies with intact membranes

OBJECTIVES

To predict when delivery will occur, within 48 h and 7 days of presentation and before 35 weeks' gestation in women presenting with threatened preterm labor.

METHODS

Sonographic measurement of cervical length was carried out in 510 women with singleton pregnancies presenting with threatened preterm labor and intact membranes at 24 to 33 + 6 weeks of gestation. The measurement was not taken into account in the subsequent management of the pregnancies. The outcome measures were delivery within 48 h and 7 days of presentation and delivery before 35 weeks.

RESULTS

The median gestation at presentation was 30 + 1 (range, 24 to 33 + 6) weeks and the median cervical length was 25 (range, 1-51) mm. Delivery within 48 h of presentation occurred in 21 (4.1%) cases, delivery within 7 days occurred in 43 (8.4%) and delivery before 35 weeks occurred in 76 (14.9%). Logistic regression analysis demonstrated that the only significant independent predictor of delivery within 48 h was cervical length (odds ratio (OR), 0.73; 95% CI, 0.65-0.81) and for delivery within 7 days the independent predictors were cervical length (OR, 0.69; 95% CI, 0.63-0.76) and vaginal bleeding (OR, 19.42; 95% CI, 3.87-97.4). In the subgroup of women who did not deliver within 7 days of presentation, the incidence of delivery before 35 weeks was 7.1% (33 of 467) and the only significant independent predictor of such delivery was cervical length (OR, 0.92; 95% CI, 0.88-0.96, P < 0.0001). There was no significant independent contribution to any of the outcome measures from ethnic group, maternal age, gestational age, body mass index, parity, cigarette smoking or use of tocolytics.

CONCLUSIONS

In women with threatened preterm labor sonographic measurement of cervical length helps to distinguish between true and false labor and to predict early preterm delivery.

What’s new and novel in obstetric anesthesia? Contributions from the 2003 scientific literature

THE PREGNANT PATIENT: Age; maternal disease; prophylactic antibiotics; gastroesophageal reflux; obesity; starvation; genotyping; coagulopathy; infection; substance abuse; altered drug responses in pregnancy; physiological changes of pregnancy. THE FETUS: Fetal monitoring; intrauterine surgery. THE NEWBORN: Breastfeeding; maternal infection, fever, and neonatal sepsis evaluation. OBSTETRIC COMPLICATIONS: Embolic phenomena; hemorrhage; preeclampsia; preterm delivery. OBSTETRIC MANAGEMENT: External cephalic version and cervical cerclage; elective cesarean delivery; fetal malpresentation; vaginal birth after cesarean delivery; termination of pregnancy. OBSTETRIC ANESTHESIA: Analgesia for labor and delivery; anesthesia for cesarean delivery; anesthesia for short obstetric operations; complications of anesthesia. MISCELLANEOUS: Consent; ethics; history; labor support; websites/books/leaflets/journal announcements.

[Prevention of recurrent preterm birth: a comeback for progesterone?]

Progesterone has been prescribed for many years in women with preterm labor despite the lack of benefit for the fetus or neonate. The description of increased risk of intrahepatic cholestasis of pregnancy led to discontinuation of this prescription. Recently, several double-blind randomized trials have focused on the usefulness of progesterone for the prevention of recurrent preterm birth. In this review, we re-examine the pathophysiological rationale for the use of progesterone and discuss the biases and limitations of older studies, detailing two recent randomized trials which suggest use of progesterone should be revisited. Data from these trials appear to provide convincing evidence that preventive use of 17 alpha-hydroxyprogesterone administered by injections early in the course of pregnancy is effective only for women with a history of preterm delivery. This prescription could be part of a more global preventive strategy together with cervical cerclage and preventive treatment of bacterial vaginitis. During treatment, it is advisable to search for secondary hepatic effects. Conversely, there are still no data favoring the use of progesterone for preterm labor. Most preterm deliveries occurring in women without a history of preterm birth preventive use of progesterone should remain a rare indication.

The changing role of progesterone in preterm labour

Progesterone is an essential hormone in the process of reproduction. It is involved in the menstrual cycle, implantation and is essential for pregnancy maintenance. Although the pharmacokinetics and pharmacodynamics of progesterone have been well studied, and since 1935 it has been synthesised and is now available commercially, its use in the pathophysiology of pregnancy remains controversial. One of these concerns is the way in which the hormone is administered, with parenteral use proving the best way to obtain optimal plasma levels. Another concern is the paucity of randomised controlled trials and the different dosages and populations studied. As a result, the therapeutic application of progesterone in pregnancy is restricted to the prevention and treatment of threatened miscarriage, recurrent miscarriage and preterm birth. Progesterone is efficacious when continuation of pregnancy is hampered by immunological factors, luteinic and neuroendocrine deficiencies and myometrial hypercontractility. This may explain the reduction in the incidence of preterm birth in high risk pregnant women using high-dosage prophylactic progesterone.

Can antibiotics prevent preterm birth-the pro and con debate

Studies using different diagnostic methods and outcome parameters have used different antibiotics and dose/administration regimes to women of differing risk of preterm birth with, not surprisingly, different results. Studies which have shown benefit have been criticised for having either poor methodology, low sample size or having only showed benefit after a non-prespecified subgroup analysis. Studies which have failed to show any benefit have been criticised for unacceptable methods of diagnosing abnormal genital tract flora or having excluded a large percentage of patients eligible for the study, for having permitted a long period to elapse from diagnosis of abnormal genital tract flora to administration of treatment and for having employed treatment too late in pregnancy. A Cochrane Systematic Review of these studies failed to provide a definitive answer because this was published one month before two randomised double-blind placebo-controlled trials were published, in which clindamycin used either systemically or intravaginally in low risk, unselected women resulted in a 60% reduction in the incidence of preterm birth. This would have influenced the inconclusive results of the Cochrane review, with respect to general population studies. Very early spontaneous preterm labour and preterm birth is more likely to be of infectious aetiology than preterm birth just before term. The earlier in pregnancy at which abnormal genital tract flora is detected, the greater is the risk of an adverse outcome. Women with abnormal flora in early pregnancy, who subsequently revert to normal, continue to have a high risk of adverse outcome of pregnancy, at a degree similar to women with abnormal genital tract flora in early pregnancy who were treated with placebo. This suggests that whatever damage abnormal flora induces, this is at an early gestation, even if the flora subsequently reverts to normal. It follows therefore that if antibiotics are to be of help in preventing spontaneous preterm labour and preterm birth of infectious aetiology, these must be administered early in pregnancy. Antibiotics used prophylactically for the prevention of preterm birth are more likely to be successful if: they are used in women with abnormal genital tract flora (rather than other risk factors for preterm birth, e.g. low BMI, twins, generic previous preterm birth); they are used early in pregnancy prior to infection (tissue penetration/inflammation and tissue damage); they are used in women with the greatest degree of abnormal genital tract flora; and if they are used in women with a predisposition to mount a damaging inflammatory response to infection.

Bronchopulmonary dysplasia in preterm infants: pathophysiology and management strategies

Bronchopulmonary dysplasia (BPD) has classically been described as including inflammation, architectural disruption, fibrosis, and disordered/delayed development of the infant lung. As infants born at progressively earlier gestations have begun to survive the neonatal period, a 'new' BPD, consisting primarily of disordered/delayed development, has emerged. BPD causes not only significant complications in the newborn period, but is associated with continuing mortality, cardiopulmonary dysfunction, re-hospitalization, growth failure, and poor neurodevelopmental outcome after hospital discharge. Four major risk factors for BPD include premature birth, respiratory failure, oxygen supplementation, and mechanical ventilation, although it is unclear whether any of these factors is absolutely necessary for development of the condition. Genetic susceptibility, infection, and patent ductus arteriosus have also been implicated in the pathogenesis of the disease. The strategies with the strongest evidence for effectiveness in preventing or lessening the severity of BPD include prevention of prematurity and closure of a clinically significant patent ductus arteriosus. Some evidence of effectiveness also exists for single-course therapy with antenatal glucocorticoids in women at risk for delivering premature infants, surfactant replacement therapy in intubated infants with respiratory distress syndrome, retinol (vitamin A) therapy, and modes of respiratory support designed to minimize 'volutrauma' and oxygen toxicity. The most effective treatments for ameliorating symptoms or preventing exacerbation in established BPD include oxygen therapy, inhaled glucocorticoid therapy, and vaccination against respiratory pathogens.Many other strategies for the prevention or treatment of BPD have been proposed, but have weaker or conflicting evidence of effectiveness. In addition, many therapies have significant side effects, including the possibility of worsening the disease despite symptom improvement. For instance, supraphysiologic systemic doses of glucocorticoids lessen the incidence of BPD in infants at risk for the disease, and promote weaning of oxygen and mechanical ventilation in infants with established BPD. However, the side effects of systemic glucocorticoid therapy, most notably the recently recognized adverse effects on neurodevelopment, preclude their routine use for the prevention or treatment of BPD. Future research in BPD will most probably focus on continued incremental improvements in outcome, which are likely to be achieved through the combined effects of many therapeutic modalities.

Estimated Effect of 17 Alpha-Hydroxyprogesterone Caproate on Preterm Birth in the United States

OBJECTIVE

A multicenter, randomized placebo-controlled trial among women with singleton pregnancies and a history of spontaneous preterm birth found that weekly injections of 17 alpha-hydroxyprogesterone caproate (17P), initiated between 16 and 20 weeks of gestation, reduced preterm birth by 33%. The current study estimated both preterm birth recurrence and the potential reduction in the national preterm birth rate.

METHODS

Using 2002 national birth certificate data, augmented by vital statistics from 2 states, we estimated the number of singleton births delivered to women eligible for 17P through both a history of spontaneous preterm birth and prenatal care onset within the first 4 months of pregnancy. The number and rate of recurrent spontaneous preterm births were estimated. To predict effect, the reported 33% reduction in spontaneous preterm birth attributed to 17P therapy was applied to these estimates.

RESULTS

In 2002, approximately 30,000 recurrent preterm births occurred to women eligible for 17P, having had a recurrent preterm birth rate of 22.5%. If 17P therapy were delivered to these women, nearly 10,000 spontaneous preterm births would have been prevented, thereby reducing the overall United States preterm birth rate by approximately 2%, from 12.1% to 11.8% (P < .001), with higher reductions in targeted groups of eligible pregnant women.

CONCLUSION

Use of 17P could reduce preterm birth among eligible women, but would likely have a modest effect on the national preterm birth rate. Additional research is urgently needed to identify other populations who might benefit from 17P, evaluate new methods for early detection of women at risk, and develop additional prevention strategies.

LEVEL OF EVIDENCE

III.

Preventing Preterm Birth: What Works, What Doesn???t

Preterm birth is one of the most important problems in medicine today with an alarming frequency and economic impact. This paper reviews recent research findings specifically addressing the following primary and secondary prevention interventions: cerclage placement, detection and treatment of infections, progesterone administration, antibiotics in preterm labor and the use of tocolysis. The effectiveness of these interventions is presented in terms of the number needed to treat and number needed to harm. At the present, most of our interventions fail to demonstrate benefit in terms of prevention of preterm birth and improvement of neonatal outcomes. Use of progesterone may hold promise, but whether we will develop effective interventions to reduce risks for all women remains to be seen.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians

LEARNING OBJECTIVES

After completion of this article, the reader should be able to summarize the epidemiology of preterm births in the U.S., to outline the primary preventive measures for preterm birth, and to interpret the relative effectiveness of the various preventive measures.

Progestational Agents to Prevent Preterm Birth: A Meta-Analysis of Randomized Controlled Trials

OBJECTIVE

To perform an updated systematic review with meta-analysis to further elucidate the efficacy of progestational agents for the prevention of preterm births in patients at elevated risk.

DATA SOURCES

Computerized databases, references in published studies, and textbook chapters in all languages were used to identify randomized controlled trials (RCTs) evaluating the use of progestational agents for the prevention of preterm births in women at elevated risk.

METHODS OF STUDY SELECTION

We identified RCTs that compared progestational agents with placebo for patients at risk for preterm birth and evaluated at least one of the following: delivery before 37 weeks of gestation, birth weight less than 2,500 g, threatened preterm labor, respiratory distress syndrome, and perinatal mortality. The primary outcomes assessed were preterm delivery and perinatal mortality.

TABULATION, INTEGRATION, AND RESULTS

Ten studies met inclusion criteria for this review. For each study with binary outcomes, an odds ratio (OR) with 95% confidence intervals (CIs) was calculated for selected outcomes. Homogeneity was tested across the studies. Compared with women allocated to receive placebo, those who received progestational agents had lower rates of preterm delivery (26.2% versus 35.9%; OR 0.45, 95% CI 0.25-0.80). Similar results were noted when comparing patients who were specifically treated with 17alpha-hydroxyprogesterone caproate (29.3% versus 40.9%; OR 0.45, 95% CI 0.22-0.93). Additionally, subjects allocated to receive 17alpha-hydroxyprogesterone caproate had lower rates of birth weights less than 2,500 g (OR 0.50, 95% CI 0.36-0.71). No differences in rates of hospital admissions for threatened preterm labor or perinatal mortality were noted for subjects receiving progestational agents in general or for those receiving only 17alpha-hydroxyprogesterone caproate specifically.

CONCLUSION

The use of progestational agents and 17alpha-hydroxyprogesterone caproate reduced the incidence of preterm birth and low birth weight newborns.

Progesterone enhances the tocolytic effect of ritodrine in isolated pregnant human myometrium

OBJECTIVE

To evaluate the effect of natural progesterone on the relaxant effect of ritodrine on pregnant human oxytocin-induced myometrial contractility.

STUDY DESIGN

Isometric tension recordings were performed under physiologic conditions on isolated myometrial strips taken from low-risk term pregnant women undergoing elective cesarean section. Cumulative effects of natural progesterone (10 (-11) to 10 (-5) mol/L) on oxytocin-induced myometrial contractility were evaluated. Contractile activity following ritodrine exposure was also investigated in myometrium pretreated with natural progesterone.

RESULTS

Natural progesterone alone exerted a concentration-dependent relaxant effect on myometrial contractions. The concentration-response curve for ritodrine from natural progesterone pretreated myometrium was shifted to the left with a significant reduction ( P < .01) of 50% of the maximal response, contraction amplitude ( P < .05), and frequency ( P < .05). However, there was no significant difference in the mean maximal inhibition achieved ( P = .95).

CONCLUSION

Natural progesterone increased the relaxant effect of ritodrine by reducing 50% of the maximal response, amplitude, and frequency of myometrial contraction, most likely through nongenomic actions. These results suggest that natural progesterone may be beneficial for preventing preterm birth in a low-risk population.

Progesterone treatment to prevent preterm birth

The publication in 2003 of two large randomised trials of progesterone therapy to prevent preterm delivery has generated renewed interest in this treatment and has added substantial numbers of subjects to previously published small trials. The randomised trials of progestogens have generally shown efficacy in reducing the rate of recurrent preterm delivery in women with singleton pregnancies who were at high risk for preterm labour and delivery. Most of the successful trials have employed 17alpha-hydroxyprogesterone caproate, and one trial has reported positive results using progesterone vaginal suppositories. The administration of 17alpha-hydroxyprogesterone caproate or progesterone suppositories to women with these high-risk pregnancies showed a significant protective effect for preterm birth in six of the seven published trials. No successful trials of progestogens have been reported for women at risk for preterm delivery because of multiple gestations. Trials of progestogens after the occurrence of symptoms of labour have shown them to be ineffective in prolonging pregnancy.

17 alpha-hydroxyprogesterone caproate versus intravaginal progesterone in IVF-embryo transfer cycles: a prospective randomized study

One of the main issues in the management of IVF and embryo transfer techniques is to ensure adequate concentrations of progesterone. The aim of this prospective, randomized study was to compare the effectiveness of 17 alpha -hydroxyprogesterone caproate (17-HPC) administered intramuscularly and intra-vaginal progesterone in gel in luteal phase support in patients undergoing IVF-embryo transfer cycles. A total of 320 patients were randomly treated with either 17-HPC (341 mg i. m. every 3 days) or progesterone vaginal gel (90 mg daily). The inclusion criteria were the use of gonadotrophin-releasing hormone down-regulation and age <40 years. The outcome of IVF in both study groups was evaluated for implantation rate, biochemical pregnancy, clinical pregnancy, miscarriage, and ongoing pregnancy rate. The results of this study showed that 17-HPC conferred more benefit to IVF-embryo transfer cycles compared with intra-vaginal progesterone, as demonstrated by the results of most of the main outcome parameters considered. The data showed that 17-HPC administered every 3 days appears to be more effective in providing luteal support in comparison to intra-vaginal progesterone.