What's new concerning the epidemiology and prevention of preterm birth? This easy-to-navigate collection of recent MEDLINE abstracts highlights research and current thinking about the epidemiology of preterm birth and prevention of preterm labor and delivery. Epidemiology Defining the Problem: the Epidemiology of Preterm Birth Lumley J Br J Obstet Gynaecol. 2003;110(Suppl 20):3-7 Preterm birth is the major clinical problem associated with perinatal mortality, serious neonatal morbidity and moderate to severe childhood disability in prosperous countries. Its prevalence is affected by the way in which gestational age is assessed, by national differences in the registration of births, associated practices, such as burial costs, or maternity benefits, which encourage or discourage registration, and by the perceived viability of extremely preterm infants. Despite these uncertainties, there is reliable evidence that preterm births are increasing, especially births before 28 weeks gestation. Contributing factors include births following assisted reproductive therapy and ovulation induction, especially multiple births, and the increasing proportion of births among women >34 years. On the other hand, improvements in neonatal care have substantially increased the survival of preterm infants during the last 15 years. There is wider acceptance of the importance of infection as a factor in preterm birth, and increasing recognition that processes leading to preterm birth may be initiated in very early pregnancy (the initiation of pre-eclampsia, major birth defects, premature placental separation), or even prior to pregnancy (prior pregnancy losses). It is unclear whether the familiar clinical presentations of preterm labour and birth reflect different pathophysiological processes. The pathways which link those processes to the consistent pattern of social differences in the probability of preterm birth have prompted new research approaches but in 2002 'the stubborn challenge of preterm birth' remains just that. Classification and Heterogeneity of Preterm Birth Moutquin JM Br J Obstet Gynaecol. 2003;110(Suppl 20):30-33 Three main conditions explain preterm birth: medically indicated (iatrogenic) preterm birth (25%; 18.7-35.2%), preterm premature rupture of membranes (PPROM) (25%; 7.1-51.2%) and spontaneous (idiopathic) preterm birth (50%; 23.2-64.1%). The majority of multiple pregnancies (10% of all preterm births) are delivered preterm (50% for medical reasons). Although medical indications relate more to feto-maternal conditions, PPROM to infections and idiopathic preterm birth to lifestyle, these risk factors are identified in any category, emphasising that preterm birth has a multifactorial origin. Still, several incidences of preterm birth are not completely explained with a plausible cause for PPROM or spontaneous preterm labour suggesting that other causes have yet to be identified. In addition, preterm birth is associated with unrecognised severe congenital anomalies. Variability within the main categories may be explained by the studied population, ethnic group, social class and preventive interventions towards reducing spontaneous preterm birth where the proportion of medically-indicated preterm birth is increased. Despite being retrospective a classification according to gestational age at birth is important for neonatal prognosis. Preterm birth is stratified into mild preterm (32-36 weeks), very preterm (28-31 weeks) and extremely preterm (<28 weeks) with increasing neonatal mortality and morbidity. Recent studies suggested that infection was mostly responsible for extreme preterm birth, while stress and lifestyle accounted for mild preterm birth, and a mixture of both conditions contributed to very preterm birth. Are Reported Preterm Birth Rates Reliable? An Analysis of Interhospital Differences in the Calculation of the Weeks of Gestation at Delivery and Preterm Birth Rate Balchin I, Whittaker JC, Steer PJ, Lamont RF Br J Obstet Gynaecol. 2004;111:160-163 We investigated the possibility of preterm birth misclassification as a determinant of variation in its reported rates. Using a database of 497,105 deliveries from 17 hospitals, the best estimate of gestational age made at delivery and entered into the database at that time was recalculated from the menstrual dates and mid-trimester ultrasound scan. The recalculated completed weeks of gestation at delivery was compared with that made at birth. Calculation of estimated gestational age varied between hospitals due to inconsistencies in 'rounding' and 'truncating' the weeks of gestation at delivery. This resulted in preterm birth misclassification rates of up to 10.1%. The Cost of Prematurity: Quantification by Gestational Age and Birth Weight Gilbert WM, Nesbitt TS, Danielsen B Obstet Gynecol. 2003;102:488-492 Objective: To determine gestational age- and birth weight-related pregnancy outcomes and resource use associated with prematurity in surviving neonates. Methods: A data set linking birth certificates with maternal and newborn hospital discharge records from hospitals in California (from January 1, 1996, to December 31, 1996) was examined for all singleton deliveries by gestational age (weekly, from 25 to 38 weeks) and birth weight (by 250-g increments from 500 to 3000 or more g). Records were examined for respiratory distress syndrome (RDS), use of mechanical ventilation, length of hospital stay in days, and hospital costs. Results: As expected, RDS, ventilation, length of hospital stay, and costs per case decreased exponentially with increasing gestational age and birth weight. Specifically, neonatal hospital costs averaged 202,700 dollars for a delivery at 25 weeks, decreasing to 2600 dollars for a 36-week newborn and 1100 dollars for a 38-week newborn. Neonatal costs were 224,400 dollars for a newborn at 500-700 g, decreasing to 4300 dollars for a newborn at 2250-2500 g and 1000 dollars for a birth weight greater than 3000 g. For each gestational age group from 25 to 36 weeks, total neonatal costs were similar, despite increasing case numbers with advancing gestational age. Neonatal RDS and need for ventilation were significant at 7.4% and 6.3%, respectively, at 34 weeks' gestation. Significant "excess" costs were found for births between 34 and 37 weeks' gestational age when compared with births at 38 weeks. Conclusion: Prematurity, whether examined by gestational age or birth weight, is associated with significant neonatal hospital costs, all of which decrease exponentially with advancing gestational age. Because total costs for each gestational age group from 25 to 36 weeks were roughly the same (38,000,000 dollars), opportunity for intervention to prevent preterm delivery and decrease costs is potentially available at all preterm gestational ages. Placenta Previa: Neonatal Death After Live Births in the United States Salihu HM, Li Q, Rouse DJ, Alexander GR Am J Obstet Gynecol. 2003;188:1305-1309 Objective: The purpose of this study was to describe neonatal mortality rates among live births that were complicated by placenta previa in the United States. Study Design: This was a population-based retrospective cohort study of 1997 United States singleton live births. Neonatal deaths among pregnancies that were complicated by placenta previa were compared with deaths among pregnancies with no placenta previa. Adjusted and unadjusted hazard ratios were generated from a proportional hazards regression model. Results: Of 3,773,369 live births, 9656 were complicated by placenta previa (2.6 cases per 1000). Among cases of placenta previa, 114 neonatal deaths occurred (11.8 per 1000) versus 14951 (4 per 1000) among non-placenta previa neonates (P <.0001). The adjusted relative risk of death was three times higher among placenta previa neonates (hazard ratio, 3.06; 95% CI, 2.40-3.94). Placenta previa-related death was mediated through preterm delivery rather than small for gestational age. Conclusion: Placenta previa triples the rate of neonatal mortality, which is mediated mainly through preterm birth. Preterm Birth in a French Population: The Importance of Births by Medical Decision Papiernik E, Zeitlin J, Rivera L, Bucourt M, Topuz B Br J Obstet Gynaecol. 2003;110:430-432 This analysis describes the prevalence of preterm birth by medical decision among 50,307 live births from the district of Seine-Saint-Denis in France, using a classification that distinguishes between medically decided preterm births associated with premature rupture of membranes and those for other reasons. Thirty-seven percent of singleton and 28% of twin preterm births result from labour induction or a caesarean section in the absence of labour. One-quarter of singleton indicated preterm births are associated with premature rupture of membranes. Between 28 and 31 weeks of gestation, 40% of all singleton preterm births result from a medical decision not associated with premature rupture of membranes. The high levels of indicated preterm birth must be taken into account in evaluations of preterm birth rates and trends in developed countries. Infant Mortality, Low Birth Weight, and Prematurity Among Hispanic, White, and African American Women in North Carolina Leslie JC, Galvin SL, Diehl SJ, Bennett TA, Buescher PA Am J Obstet Gynecol. 2003;188:1238-1240 Objectives: The study was undertaken to compare Hispanic birth outcomes with those of white and African American women in North Carolina and to examine variables associated with adverse birth outcomes among Hispanic women. Study Design: Retrospective comparison of birth outcomes by ethnicity/race, from linked birth/infant death certificates in North Carolina (1993-1997) was conducted. Multivariate, binary logistic regression and chi(2) analysis were used to examine relationships between available medical and sociodemographic index values and composite birth outcomes among Hispanic women. Results: Infant mortality rates were lowest among Hispanic women. Low birth weight and prematurity rates were similar to those of white women and lower than those of African American women. Variables significantly related to healthy composite birth outcomes among Hispanic women included higher education, no preterm delivery history, prenatal care, marriage, and no daily tobacco use. Conclusion: Hispanic birth outcomes in North Carolina were better than those of African American women and similar to those of white women, despite use of prenatal care and socioeconomic characteristics similar to African American women.
Prevention Looking to the Future Lamont RF Br J Obstet Gynaecol. 2003;110(Suppl 20):131-135 Since the 7th and 13th Study Groups of the Royal College of Obstetricians and Gynaecologists met in 1977 and 1985, respectively, no meeting of this magnitude has convened to discuss the problems of spontaneous preterm labour and delivery and the associated fetomaternal mortality and morbidity. In the 17 years or so since that time, advances have been made in our understanding of the mechanisms of labour, the role of infection, the benefit of antepartum corticosteroids and the development of safer more specific tocolytics. In the future, an understanding of the genetic risk of spontaneous preterm labour and preterm birth is essential, particularly with respect to the predisposition to produce potentially damaging pro-inflammatory cytokines. The examination of the tissue damage will require pathologists specifically trained in perinatal pathology if the aetiology is to be ascertained and future management tailored to the risks. A greater understanding of fetomaternal immunology and response to antigen exposure in pregnancy may help us to understand which fetomaternal pairs are at greatest risk of responding by delivering preterm, with greater or lesser tissue damage than others with similar risk. Specifically, the relation between spontaneous preterm labour and proteinuric pre-eclampsia with their common immunology, inflammatory response and tissue damage leading to either spontaneous preterm labour or iatrogenic preterm birth will need to be addressed. This meeting has been very clinically and obstetrically orientated, in future we will need to involve epidemiologists, neonatologists, microbiologists, genito-urinary medicine physicians, immunologists, geneticists, biochemists, physiologists and endocrinologists. Although spontaneous preterm labour and preterm birth are the major causes of perinatal mortality and morbidity in the developed world, the definition and management protocols for spontaneous preterm labour varies from unit to unit and country to country. A process has already begun, hopefully fuelled by this meeting and those attending, to develop an international consensus on definitions and evidence-based practical guidelines on the management of spontaneous preterm labour. Perhaps in the longer term it may be possible to influence standards of care, outcome measures and training across international boundaries.
Prenatal Care The Impact of Prenatal Care on Preterm Births Among Twin Gestations in the United States, 1989-2000 Vintzileos AM, Ananth CV, Smulian JC, Scorza WE Am J Obstet Gynecol. 2003;189:818-823 Objective: The purpose of this study was to determine the association between prenatal care and preterm births among twin gestations in the presence and absence of high-risk pregnancy conditions. Study Design: Twin birth data in the United States were used to determine the association between preterm birth and prenatal care with the use of logistic regression. Results: Of the 779,387 twin births, 54.7% twin births were delivered preterm. The rate was higher among black women than among white women in the presence (57.0% vs 51.2%, respectively) and absence (70.3% vs 61.6%, respectively) of prenatal care. The absence of prenatal care increased the relative risk for preterm birth by 1.24-fold among black women and by 1.22-fold among white women. Lack of prenatal care was associated with increased preterm birth rates in the presence of most high-risk conditions. Conclusion: Prenatal care is associated with fewer twin preterm births in the presence and absence of high-risk conditions. Increased prenatal care participation may help decrease preterm birth rates and also narrow the black-white twin preterm birth disparity. Specialized Prenatal Care and Maternal and Infant Outcomes in Twin Pregnancy Luke B, Brown MB, Misiunas R, et al Am J Obstet Gynecol. 2003;189:934-938 Objective: This study was undertaken to evaluate the effect of a prenatal nutrition and education program on twin pregnancy, neonatal, and early childhood outcomes. Study Design: This prospective intervention study of women who participated in a specialized program (Program Pregnancies) versus nonparticipants included twice-monthly visits, dietary prescription of 3000 to 4000 kcal per day, multimineral supplementation, and patient education. Results: Program Pregnancies were associated with improved pregnancy outcomes (preeclampsia, adjusted odds ratio [AOR] 0.41, 95% CI, 0.23-0.75; preterm premature rupture of membranes, AOR 0.35, 95% CI, 0.20-0.60; delivery <36 weeks, AOR 0.62, 95% CI, 0.43-0.89; low birth weight, AOR 0.42, 95% CI, 0.29-0.61), significantly longer gestations (+7.6 days), higher birth weights (+220 g), lower neonatal morbidity (retinopathy of prematurity, necrotizing enterocolitis, intraventricular hemorrhage, or ventilator support, AOR 0.44, 95% CI, 0.31-0.62), length of stay (-5.3 days), and cost per twin (-14,023 dollars). Through 3 years of age, program children were significantly less likely to be rehospitalized (AOR 0.31, 95% CI, 0.11-0.91) or to be developmentally delayed (AOR 0.65, 95% CI, 0.44-0.96). Conclusion: Program participation was associated with improved outcomes at birth and through age 3 years.
Bacterial Vaginosis Treatment The Potential for Probiotics to Prevent Bacterial Vaginosis and Preterm Labor Reid G, Bocking A Am J Obstet Gynecol. 2003;189:1202-1208 Infections of the urogenital tract in women represent a major burden on the quality of life of women and on the health care system of Canada and other countries. Complications arising from bacterial vaginosis (BV) include increased risk of sexually transmitted diseases including human immunodeficiency virus and elevated risk of preterm birth (PTB). Pharmaceutical interventions, such as antibiotics, have been suboptimally effective and have failed to reduce the incidence of PTB. The absence of lactobacilli in the vagina, a specific feature of BV, raises the question as to whether restoration of lactobacilli, by probiotic therapy, can restore the normal flora and improve the chances of having a healthy term pregnancy. The rationale for probiotic use in pregnant women is quite strong. Certain lactobacilli strains can safely colonize the vagina after oral and vaginal administration, displace and kill pathogens including Gardnerella vaginalis and Escherichia coli, and modulate the immune response to interfere with the inflammatory cascade that leads to PTB. Additional attributes of probiotics include their potential to degrade lipids and enhance cytokine levels, which promote embryo development. In a society that focuses on disease rather than health and drug therapy rather than natural preventive measures, it will take some effort to get remedies such as probiotics into mainstream care. Perhaps the escalating health care budgets and emergence of "superbugs" will provide the incentives to put in place clinical trials designed to evaluate how best to use the commensal organisms that, after all, make up more of our body than human cells, and without which none of us would survive. Effect of Early Oral Clindamycin on Late Miscarriage and Preterm Delivery in Asymptomatic Women With Abnormal Vaginal Flora and Bacterial Vaginosis: A Randomised Controlled Trial Ugwumadu A, Manyonda I, Reid F, Hay P Lancet. 2003;361:983-988 Background: Abnormal vaginal flora and bacterial vaginosis are associated with amplified risks of late miscarriage and spontaneous preterm delivery. We aimed to establish whether antibiotic treatment early in the second trimester might reduce these risks in a general obstetric population. Methods: We screened 6120 pregnant women attending hospital for their first antenatal visit — who were at 12-22 weeks' gestation (mean 15.6 weeks) — for bacterial vaginosis or abnormal vaginal flora. We used gram-stained slides of vaginal smears to diagnose abnormal vaginal flora or bacterial vaginosis, in accordance with Nugent's criteria. We randomly allocated 494 women with one of these signs to receive either clindamycin 300 mg or placebo orally twice daily for 5 days. Primary endpoints were spontaneous preterm delivery (birth > or =24 but <37 weeks) and late miscarriage (pregnancy loss > or =13 but <24 weeks). Analysis was intention to treat. Findings: Nine women were lost to follow-up or had elective termination. Thus, we analysed 485 women with complete outcome data. Women receiving clindamycin had significantly fewer miscarriages or preterm deliveries (13/244) than did those in the placebo group (38/241; percentage difference 10.4%, 95% CI 5.0-15.8, p=0.0003). Clindamycin also reduced adverse outcomes across the range of abnormal Nugent scores, with maximum effect in women with the highest Nugent score of 10. Interpretation: Treatment of asymptomatic abnormal vaginal flora and bacterial vaginosis with oral clindamycin early in the second trimester significantly reduces the rate of late miscarriage and spontaneous preterm birth in a general obstetric population. Intravaginal Clindamycin to Reduce Preterm Birth in Women With Abnormal Genital Tract Flora Lamont RF, Duncan SL, Mandal D, Bassett P Obstet Gynecol. 2003;101:516-522 Objective: To assess the ability of clindamycin vaginal cream to reduce the incidence of preterm birth in women with abnormal genital tract flora in the second trimester of pregnancy. Methods: This was a randomized, double-blind, placebo-controlled, tricenter study. A total of 409 women with abnormal genital tract flora on Gram stain of vaginal secretions at 13-20 weeks' gestation were randomized to receive a 3-day course of clindamycin vaginal cream or placebo. Those women who still had abnormal vaginal flora 3 weeks later received a 7-day course of the original study drug (ie, either clindamycin vaginal cream or placebo as per original randomization). The primary outcome measure was the incidence of preterm birth. Results: There was a statistically significant reduction in the incidence of preterm birth in the clindamycin vaginal cream group (4%) compared with placebo (10%) (P <.03). Significantly more babies born preterm (63%) required admission to the neonatal intensive care unit compared with term infants (4%) (P <.001). Conclusion: A 2% clindamycin vaginal cream, when compared with placebo administered to women with abnormal genital tract flora before 20 weeks' gestation, can reduce the incidence of preterm birth by 60% and hence the need for neonatal intensive care. Antibiotic Treatment of Bacterial Vaginosis In Pregnancy: A Meta-Analysis Leitich H, Brunbauer M, Bodner-Adler B, Kaider A, Egarter C, Husslein P Am J Obstet Gynecol. 2003;188:752-758 Objective: The purpose of this study was to evaluate the effectiveness of antibiotic treatment of bacterial vaginosis in pregnancy to reduce preterm delivery. Study Design: We performed a meta-analysis of published, English-language, randomized, placebo-controlled clinical trials of antibiotic treatment of bacterial vaginosis in pregnant women with intact amniotic membranes at <37 weeks of gestation. Primary outcomes included preterm delivery, perinatal or neonatal death, and neonatal morbidity. Results: Ten studies with results for 3969 patients were included. In patients without preterm labor, antibiotic treatment did not significantly decrease preterm delivery at <37 weeks of gestation, in all patients combined (odds ratio, 0.83; 95% CI, 0.57-1.21) nor in high-risk patients with a previous preterm delivery (odds ratio, 0.50; 95% CI, 0.22-1.12). In both groups, significant statistical heterogeneity was observed. A significant reduction in preterm delivery and no statistical heterogeneity were observed in 338 high-risk patients who received oral regimens with treatment durations of > or =7 days (odds ratio, 0.42; 95% CI, 0.27-0.67). Nonsignificant effects and no statistical heterogeneity were observed in low-risk patients (odds ratio, 0.94; 95% CI, 0.71-1.25) and with vaginal regimens (odds ratio, 1.25; 95% CI: 0.86-1.81). In one study antibiotic treatment in patients with preterm labor led to a nonsignificant decrease in the rate of preterm deliveries (odds ratio, 0.31; 95% CI, 0.03-3.24). Conclusion: The screening of pregnant women who have bacterial vaginosis and who have had a previous preterm delivery and treatment with an oral regimen of longer duration can be justified on the basis of current evidence. More studies are needed to confirm the effectiveness of this strategy, both in high-risk patients without preterm labor and in patients with preterm labor. Infection in the Prediction and Antibiotics in the Prevention of Spontaneous Preterm Labour and Preterm Birth Lamont RF Br J Obstet Gynaecol. 2003;110(Suppl 20):71-75 The association between infection and spontaneous preterm labour is now well established and thought to be responsible for preterm birth in up to 40% of cases. Preterm labour that is due to infection is refractory to the use of tocolytic agents. So the knowledge that infection may be the cause is unhelpful once a woman is admitted in spontaneous preterm labour, since by that time there may be irreversible changes in the uterine cervix, which renders futile those attempts to inhibit the process. It would be much more logical to use the association between infection and spontaneous preterm labour to identify a group of women at risk and to intervene using antibiotic prophylaxis. It is important to record, that the earlier in gestation at which abnormal genital tract colonisation is detected, the greater is the risk of an adverse outcome. For example, abnormal genital tract flora at 26-32 weeks gestation is associated with preterm birth with an odds ratio (OR) of 1.4 to 2, whereas abnormal genital tract flora at 7-16 weeks gestation carries an OR of 5 to 7.5. Intervention studies have used different antibiotics in different dosage regimes by different routes of administration to patients of differing risks at different gestational ages. Not surprisingly this has led to differing results. If intervention is to be successful, the antibiotics chosen should be active against bacterial vaginosis or bacterial vaginosis-related organisms and should be used early in pregnancy in those women with the greatest degree of abnormal genital tract flora. While there is logic in using intravaginal antibiotics to deliver a heavy antibiotic load to the vagina where heavy abnormal colonisation exists, there is also logic in considering systemic antibiotics to eradicate those organisms, which have already gained access to the decidua. It may be that the greatest chance of benefit would exist if both routes of administration were combined. Yet no study has evaluated the combination of both intravaginal and systemic antibiotics to eradicate abnormal genital tract flora for the prevention of preterm birth.
Omega 3 Fatty Acid Supplementation A Randomized Trial of Docosahexaenoic Acid Supplementation During the Third Trimester of Pregnancy Smuts CM, Huang M, Mundy D, Plasse T, Major S, Carlson SE Obstet Gynecol. 2003;101:469-479 Objective: To hypothesize that higher intake of docosahexaenoic acid, an n-3 long chain polyunsaturated fatty acid, would increase duration of gestation and birth weight in US women. Methods: This was a randomized, double-blind, controlled, clinical trial. Subjects were enrolled in an ambulatory clinic where they received prenatal care. This was a population-based sample. Most subjects received government assistance for medical care and most were black (73%). Subjects were enrolled between the 24th and 28th week of pregnancy and consumed docosahexaenoic acid (33 or 133 mg) from eggs until parturition. Gestational age and birth weight were the main study outcomes. Infant length and head circumference, preterm birth, and low birth weight were secondary outcomes. Results: Eighty-three percent of subjects completed the study (291 of 350 enrolled). No subject was discontinued for an adverse event. After controlling for important predefined risk factors and confounding variables, gestation increased by 6.0 ± 2.3 days (P =.009) in the higher docosahexaenoic acid group. Birth weight, length, and head circumference increased, but did not reach statistical significance (P =.06-.18), although the increases could be clinically important indications of enhanced intrauterine growth. No safety concerns were raised by the study. Conclusion: Duration of gestation increased significantly when docosahexaenoic acid intake was increased during the last trimester of pregnancy. The increase in gestation was similar to that reported for interventions with much larger amounts of n-3 long chain polyunsaturated fatty acids. Medscape Ob/Gyn & Women's Health 8(1), 2004. © 2004 Medscape This is a part of article MEDLINE Abstracts: Preterm Birth - Epidemiology and Prevention Taken from "Cleocin Clindamycin Investigations Archive" Information Blog |