Late preterm birth and previous cesarean section: a population-based cohort study

Background: Late preterm birth (LPB) is increasingly common and associated with higher morbidity and mortality than term birth. Yet, little is known about the influence of previous cesarean section (PCS) and the occurrence of LPB in subsequent pregnancies. We aim to evaluate this association along with the potential mediation by cesarean sections in the current pregnancy.

Methods: We use population-based birth registry data (2005–2012) to establish a cohort of live born singleton infants born between 34 and 41 gestational weeks to multiparous mothers. PCS was the primary exposure, LPB (34–36 weeks) was the primary outcome, and an unplanned or emergency cesarean section in the current pregnancy was the potential mediator. Associations were quantified using propensity weighted multivariable Poisson regression, and mediating associations were explored using the Baron-Kenny approach.

Results: The cohort included 481,531 births, 21,893 (4.5%) were LPB, and 119,983 (24.9%) were predated by at least one PCS. Among mothers with at least one PCS, 6307 (5.26%) were LPB. There was increased risk of LPB among women with at least one PCS (adjusted Relative Risk (aRR): 1.20 (95%CI [1.16, 1.23]). Unplanned or emergency cesarean section in the current pregnancy was identified as a strong mediator to this relationship (mediation ratio?=?97%).

Conclusions: PCS was associated with higher risk of LPB in subsequent pregnancies. This may be due to an increased risk of subsequent unplanned or emergency preterm cesarean sections. Efforts to minimize index cesarean sections may reduce the risk of LPB in subsequent pregnancies.     

早产影响因素的多中心病例对照研究

目的探讨北京市二级专科医院早产发生的影响因素。方法以2009年8月至2010年8月期间在北京市5家二级专科医院住院分娩的早产产妇为研究对象,按照同分娩医院、产妇年龄、分娩时间进行1∶1配对,共统计早产产妇1323例和足月分娩产妇1323例,通过查阅病例、询问产妇来完成问卷调查。结果产前保健、均衡饮食、常住地址为城镇是早产的保护性因素,受教育程度低、负性生活事件、孕期性生活、前置胎盘、妊娠期糖尿病、妊娠期高血压疾病、早产史、胎膜早破是早产的危险因素。结论早产与多种因素相关,需要从个体、家庭、社会等多方面采取措施,进行广泛有效的健康教育和医疗保健服务,尽量减少和预防早产的发生。     

Obstetrician-gynecologists' knowledge of preterm birth frequency and risk factors

Objectives. To assess obstetrician-gynecologists' knowledge of preterm birth, including prevalence, risk factors, and utility of various tests in predicting increased risk.

Methods. A questionnaire was mailed to 1193 members of the American College of Obstetricians and Gynecologists.

Results. The response rate was 59%. The majority of respondents were familiar with basic preterm birth prevalence rates. However, 21% underestimated the proportion of women with presumptive preterm labor in whom preterm birth will not occur. The majority (55%) overestimated the proportion of preterm births accounted for by multiples. Twelve percent indicated bed rest as a proven method for improving newborn outcome. Respondents were fairly accurate as to which factors produce the biggest increased risk of spontaneous preterm labor or rupture of membranes; however, they tended to overestimate the risk associated with smoking, hypertension, and non-gestational diabetes. They tended to underestimate, or were unsure of, the predictive value of positive fetal fibronectin (fFN) test results or short cervical length.

Conclusions. Obstetrician-gynecologists' basic knowledge concerning preterm birth prevalence and risk factors was adequate. However, they tended to overestimate the risk associated with various maternal factors and underestimate the predictive value of various test results.     

Diabetes mellitus and the risk of preterm birth with regard to the risk of spontaneous preterm birth

Introduction.?It is internationally agreed that diabetes mellitus (DM) is associated with increased maternal and fetal morbidity and long-term complications. To avoid these complications, it is often necessary to induce birth before term. The impact of DM on spontaneous preterm birth (spontaneous labor, preterm premature rupture of membranes and/or cervical incompetence resulting in delivery before the completion of 37 gestation weeks) is still unexplained. Preterm birth accounts for the most neonatal deaths and infant morbidities, and therefore it still remains one of the biggest challenges in obstetrics.

Objective.?Our study determined if there is an increasing tendency towards spontaneous preterm birth in mothers with gestational and preexisting DM.

Methods.?In this retrospective cohort study, 187 pregnant women with gestational DM and preexisting DM were compared to a randomized control group consisting of 192 normoglycemic women concerning gestational age and perinatal outcome. Data were collected by the Medical University of Vienna. Multiple pregnancies and women with severe maternal diseases, such as preeclampsia, were excluded.

Results.?Women with DM tended significantly more often to preterm births (P?=?0.002). A significant difference in the incidence of spontaneous preterm birth was found (P?=?0.047).

Conclusion.?DM affects the length of gestation and incidence of spontaneous preterm birth.     

Maternal serum calponin 1 level as a biomarker for the short-term prediction of preterm birth in women with threatened preterm labor

Purpose: To assess the utility of maternal serum calponin 1 level in the prediction of delivery within 7 days among pregnancies complicated with threatened preterm labor.

Materials and methods: Eligible women who presented at 24–34 weeks of gestation with threatened preterm labor underwent sampling for serum calponin 1 level and cervical length measurement. They were followed up until delivery prospectively and the perinatal outcomes of the patients were recorded.

Results: Of 73 women included in the study, 36 women delivered within 7 days and 37 women delivered beyond 7 days after admission. The maternal serum calponin 1 level was significantly high in women who delivered within 7 days (p: 0.031). The threshold value of 2?ng/mL for maternal serum calponin 1 predicted delivery within 7 days with 61.1% sensitivity and 62.2 specificity (area under curve, 0.658, confidence interval 0.53–0.79). The general accuracy values for maternal cervical length measurement (≤25?mm), serum calponin 1 level (>2?ng/mL) and the combination of two tests to predict delivery within 7 days was found to be 64.4%, 61.6% and 72.1%, respectively.

Conclusions: The maternal serum calponin 1 level may be a useful biomarker in short-term prediction of preterm birth among pregnancies complicated with threatened preterm labor, in addition to cervical length measurement.     

Predicting preterm birth: a cost-effectiveness analysis

OBJECTIVE: The objective of this study was to compare the cost-effectiveness of 9 strategies for the management of threatened preterm labor. STUDY DESIGN: We derived 6 management options from the literature. These were (1) to treat all women with tocolytics and corticosteroids ("treat all"); (2) to treat all women while awaiting results of the "traditional" fetal fibronectin test results, then discontinue treatment on those with negative results; (3) to treat only those with abnormal cervical length measurements as detected by ultrasonography; (4) to treat only those with abnormal "rapid" fetal fibronectin test results; (5) to perform rapid fetal fibronectin testing and cervical length measurements and treat those with a positive result on either or both; (6) not to treat any women ("treat none"). To assess the contributions of tocolytics and corticosteroids to our outcomes, we analyzed 3 additional treatment options: (7) to treat all women with outpatient corticosteroids but not give tocolytics, (8) to administer corticosteroids to all but give tocolytics only to those with abnormal rapid fetal fibronectin test results, and (9) to administer corticosteroids to all but give tocolytics only to those with abnormal cervical length. We used decision analytic techniques to perform a cost-effectiveness analysis. RESULTS: A decision tree was constructed on the basis of these strategies. We reviewed the literature to derive all probability information. We derived sensitivity and specificity for delivery <37 weeks for fetal fibronectin and for abnormal cervical length. Outcomes of interest were respiratory distress syndrome and neonatal death. We derived cost variables from institutional statistics and from values quoted in the literature. Total costs, cases of respiratory distress syndrome, neonatal deaths, and cost-effectiveness ratios were calculated for each of the strategies. We conducted sensitivity analyses on all variables. Universal administration of outpatient corticosteroids was the least expensive option, but it resulted in more cases of respiratory distress syndrome and deaths than "treat all." Rapid fetal fibronectin plus corticosteroids, traditional fetal fibronectin, and cervical length plus corticosteroids were the next least expensive options and resulted in numbers of cases of respiratory distress syndrome and deaths that were similar to those in the "treat all" strategy. The "rapid" fetal fibronectin test, cervical length measurement, rapid fetal fibronectin test plus cervical length measurement, and "treat none" strategies resulted in more respiratory distress syndrome, more deaths, and higher costs. Treating all patients resulted in the fewest number of cases of respiratory distress syndrome and deaths but the greatest costs. CONCLUSION: Risk prediction strategies with the fetal fibronectin assay or corticosteroids plus rapid fetal fibronectin testing or cervical length assessment may offer cost savings compared with treatment of all women with threatened preterm labor and may prevent similar numbers of cases of respiratory distress syndrome and neonatal deaths.     

Identifying risk factors for very preterm birth: A reference for clinicians

Objective

to provide an accessible list of individual and population-based risk factors associated with very preterm birth to assist care providers in planning appropriate pregnancy care.

Design

a population-based case-control study.

Setting

Victoria, Australia.

Participants

women were recruited from April 2002 to 2004. Cases had a singleton birth between 20 and 31+6 weeks gestation and controls were a random selection of women having a birth of at least 37 weeks gestation in the same time period as the cases.

Measurements and findings

structured interviews were conducted within a few weeks postpartum with 603 cases and 796 controls. Data were collected on sociodemographic factors; obstetric and gynaecological history; and maternal health problems, both pre-existing and occurring during the index pregnancy. Risk factors were calculated.

Key conclusions

when correlated, risk factors were grouped as either lifestyle or maternal health factors. The majority of the risks were obstetric or gynaecological factors. Risks occurring in pregnancy may precipitate preterm birth.

Implications for practice

knowing the risk factors for very preterm birth is likely to be helpful for pregnancy care providers. The development of a risk factor checklist based on the findings presented here may enable more informed planning of care and timely intervention.     

早产临床风险因素的探讨

目的评估影响早产分娩的风险因素以及对早产干预措施影响的相关因素。方法选择2003年1月至2006年3月发生在34周前的自发性早产临产、早产胎膜早破、宫颈机能不全、先兆早产4种临床表现类型共221例,比较4种临床表现之间发病的风险因素及影响干预措施结局的相关因素。结果自发性早产临产的风险因素依次为:本次妊娠先兆流产史(OR8.917,95%CI2.308～34.457)、胎次(OR2.179,95%CI1.033～4.598)、宫颈长度改变(OR0.366,95%CI0.259～0.518);早产胎膜早破的风险因素依次为:自然流产史(OR4.922,95%CI1.115～21.720)、体外受精-胚胎移植(IVF-ET)(OR5.341,95%CI1.571～18.164);宫颈功能不全的风险因素依次为:早产史(OR9.010,95%CI2.032～39.940),IVF-ET(OR2.603,95%CI1.195～5.670)。发生早期早产分娩的影响因素依次为:血象升高(OR4.695,95%CI2.065～10.671)、宫颈长度变短(OR0.633,95%CI0.456～0.880)。对早产干预措施的影响因素为紧急宫颈环扎术(OR26.372,95%CI2.770～251.085)和血象升高(OR7.111,95%CI1.769～28.53)。结论影响早产的风险因素较多,应注重IVF-ET妊娠的早产风险;实施紧急宫颈环扎术及注重感染指标监测是减少34周前分娩的重要干预手段。     

Reducing the preterm birth rate: a population health strategy

The rate of preterm birth has been increasing in Canada and the United States. Efforts to prevent preterm birth have been largely ineffective. A population health strategy that integrates disease prevention and health promotion is needed. In this article, the five categories of health determinants proposed by the Federal, Provincial and Territorial Advisory Committee on Population Health are used as a framework to discuss risk factors and propose policies and interventions to reduce the preterm birth rate.     

Maternal dyslipidemia during pregnancy may increase the risk of preterm birth: A meta-analysis

Epidemiological studies have reported an inconsistent relationship between maternal lipid levels and preterm birth (PTB). We performed this meta-analysis to evaluate the association between maternal dyslipidemia and PTB. Overall, three nested case-control studies and eight cohort studies were eligible. Effect estimates [odds ratio(OR)/relative risk] were pooled using a fixed-effects or a random-effects model. Subgroup and metaregression analyses were conducted to evaluate the sources of heterogeneity. Eleven studies involving 13,025 pregnant women were included. Compared with pregnant women with normal lipid levels, the women with elevated levels of lipids had an increased risk of PTB, and the pooled OR was 1.68 [95% confidence interval (CI): 1.25–2.26)]; meanwhile, women with lower levels of lipids also had a trend of an increased risk of PTB (OR = 1.52, 95% CI = 0.60–3.82). The pooled ORs for elevated levels of total cholesterol, triglycerides, low density lipoprotein-cholesterol, and lower levels of high density lipoprotein-cholesterol were 1.71 (95% CI: 1.05–2.79), 1.55 (95% CI: 1.13–2.12), 1.19 (95% CI: 0.95–1.48), and 1.33 (95% CI: 1.14–1.56), respectively. The present meta-analysis found that maternal dyslipidemia during pregnancy, either the elevated total cholesterol or triglycerides, was associated with an increased risk of PTB. These findings indicate that a normal level of maternal lipid during pregnancy may reduce the risk of PTB.     

Racial disparities in cervical length for prediction of preterm birth in a low risk population

Purpose: Racial minorities experience higher rates of spontaneous preterm birth (sPTB). Our objective was to evaluate whether there are racial discrepancies in the incidence of second trimester short cervical length (≤25?mm).

Materials and methods: Retrospective cohort of women with singleton gestations without prior sPTB undergoing universal second trimester transvaginal ultrasound cervical length (CL) screening between January 2012 and December 2013. Black women were compared to non-Hispanic white women. Our primary outcome was the incidence of CL ≤25?mm. Secondary outcomes were incidence of PTB ≤37 weeks, delivery mode, birth weight and neonatal intensive care unit (NICU) admission.

Results: Black women (n?=?1092) differed from non-Hispanic white women (n?=?659) with respect to maternal age (26.0 versus 30.7 years), gravidity (3.1 versus 2.1), prepregnancy BMI (29.6 versus 25.0?kg/m²), and smoking status (9.8% versus 16%), respectively (p?Conclusions: Black women had a 2.8-fold increased risk of CL ≤25?mm compared non-Hispanic white women in a low-risk population.     

Oral micronized progesterone for prevention of preterm birth

Objective

To evaluate oral micronized progesterone (OMP) to prevent preterm birth (PTB).

Methods

A randomized, double-blind, placebo-controlled trial of 150 women with at least one PTB who received 100 mg of OMP or placebo twice a day from recruitment (18-24 weeks) until 36 weeks or delivery.

Results

PTB occurred in 29 (39.2%) women in the OMP group (n = 74) compared with 44 (59.5%) in the control group (n = 74, P = 0.002). Mean gestational age at delivery was higher in the OMP group (36.1 vs 34.0 weeks, P < 0.001). Fewer preterm births occurred between 28 and 31 weeks plus 6 days in the OMP group (RR 0.20; 95% CI, 0.05-0.73, P < 0.001). Neonatal age at delivery (34 vs 32 weeks, P < 0.001), birth weight (2400 vs 1890 g, P < 0.001), NICU stay (> 24 h, P < 0.001), and Apgar scores (P < 0.001) were more favorable in the OMP group, and fewer neonatal deaths occurred (3 vs 7, P = 0.190).

Conclusion

OMP reduced the risk of PTB between 28 and 31 weeks plus 6 days, NICU admissions, and neonatal morbidity and mortality in high risk patients.     

Risk factors for preterm birth in Vietnam.

OBJECTIVE: To identify the risk of preterm birth and possible determinants among women in Hanoi, Vietnam. METHOD: Prospective cohort study of 1709 women with singleton live births at Hanoi Obstetrics and Gynecology Hospital, Hanoi, Vietnam, June-October 2002. Logistic regression analysis was used to examine predictors of preterm birth (<37 weeks' gestation). RESULT: The risk of preterm birth was 11.8%. Physically demanding work during pregnancy, two or more prior spontaneous abortions, history of preterm birth, vaginal bleeding, inadequate prenatal care during the first 20 weeks of gestation, and history of intrauterine device use with removal less than 12 months before the current pregnancy were associated with increased risk of preterm birth (adjusted odds ratios between 1.8 and 2.6). CONCLUSION: Preterm birth is relatively frequent in this population. Beyond established risk factors, these data implicated agricultural work and physical work demands with preterm birth, as well as history of recent IUD use.     

N-acetylcysteine attenuates the maternal and fetal proinflammatory response to intrauterine LPS injection in an animal model for preterm birth and brain injury

Objective.?Maternal immune activation (MIA) is associated with preterm birth (PTB) and abnormal neurologic outcome. We hypothesized that N-acetylcysteine (NAC) would decrease PTB and neonatal brain injury acting as an anti-inflammatory.

Methods.?Pregnant CD-1 mice received intrauterine LPS or saline on day 15/20. They received NAC or saline and were monitored until delivery. Pups were followed and sacrificed on postnatal days 1/30 and brains were collected. Immunostaining for heavy-chain neurofilament protein (NF-H), myelin basic protein (MBP), and proteolipid protein (PLP) was performed. In another group, animals were sacrificed 6?h after treatment, and fetal brain, placenta, and myometrium were collected. Il-6, Il-1β, Il-10, and tumor necrosis factor (TNF)-α mRNA expression was determined. Nonparametric analysis was used for analysis, and pairwise comparisons were performed when appropriate.

Results.?Lipopolysaccharide (LPS) caused PTB (79 vs. 0%, p?<?0.005), and this was reduced by NAC [0.45 (95% CI: 0.26–0.83), p?<?0.008]. LPS increased IL-6 expression in myometrium and placenta. This was attenuated by NAC in myometrium. IL-1β, IL-6, and TNF-α expression increased in the fetal brain with LPS. LPS produced altered NF-H, MBP, and PLP staining, and these effects were attenuated by NAC.

Conclusion.?NAC attenuates inflammation in this MIA model and reduces PTB and white matter injury. It is an interesting candidate for study for prevention of PTB and neurologic injury.