Epidemiology: the changing face of preterm birth

Preterm birth, defined as a pregnancy ending at less than 37 completed weeks of gestation, is the leading cause of infant mortality in the United States. The occurrence of preterm births rose steadily from 9.4% of all pregnancies in the United States in 1981 to 12.8% in 2006, before declining to 12.7% in 2007 and 12.3% in 2008. Most of the increase was attributable to increases in multiple gestations. Recent research has sought to understand this condition by evaluating its familial occurrence and both clinical and pathologic information to derive an etiologically homogeneous categorization.     

A case control study of risk factors and neonatal outcomes of preterm birth

Objective

The aim is to examine risk factors and neonatal outcomes of preterm birth and to provide basis in preventing preterm birth.

The global epidemiology of preterm birth

This article is a part of a series that focuses on the current state of evidence and practice related to preterm birth prevention. We provide an overview of current knowledge (and limitations) on the global epidemiology of preterm birth, particularly around how preterm birth is defined, measured, and classified, and what is known regarding its risk factors, causes, and outcomes. Despite the reported associations between preterm birth and a wide range of socio-demographic, medical, obstetric, fetal, and environmental factors, approximately two-thirds of preterm births occur without an evident risk factor. Efforts to standardize definitions and compare preterm birth rates internationally have yielded important insights into the epidemiology of preterm birth and how it could be prevented.     

Analysis of pregnancy outcomes in patients undergoing ultrasound-indicated cerclage and identification the influence factors for predicting preterm birth: A retrospective study of 87 cases

ObjectiveTo investigate the factors influencing preterm birth in patients after ultrasound-indicated cerclage with different cervical lengths (CL), and explore the optimal cut-off value of CL.Materials and methodsThe retrospective study included 87 pregnant women with a history of preterm birth and second-trimester loss that received ultrasound-indicated cerclage in our hospital between January 2004 and April 2021. Groups were divided by CL at the demarcation point of 1.0, 1.5 and 2.0 cm respectively. The pregnancy outcomes were compared. Logistic regression analysis was performed to assess the independent influence factors. Receiver–operating characteristic (ROC) curves were constructed and the area under the curve (AUC) was used to compare the prediction capability of the associated factors.ResultsSignificant difference was found in terms of patients delivered at ≥32 weeks of gestation (19 [55.9%]vs. 41 [77.4%], p < 0.05) and neonatal birth weight (2495 [1138,3185]vs. 2995 [2155,3235] g, p < 0.05), when the CL was categorized at the demarcation point of 1.5 cm. Body mass index (BMI) (odds ratio [OR] = 1.224, p < 0.05), a history of preterm birth and second-trimester loss (OR = 3.153, p < 0.05), and C-reactive protein (CRP) > 5 mg/L (OR = 8.097, p < 0.05) were independent risk factors for gestational age more than 28 weeks. The AUC of joint predictor A included those factors was 0.849 (95% CI: 0.701–0.998, p < 0.05). CRP>5 mg/L was found to be a significant independent risk factor for different gestational age at delivery.ConclusionsA CL of 1.5 cm was the optimal cut-off value that could help women who underwent serial CL surveillance choose ultrasound-indicated cerclage at an appropriate time. High BMI, more history of preterm birth and second-trimester loss and abnormal CRP could be used as combined predictors to recognize the risk of preterm birth (<28 weeks) post-surgery.     

感染相关早产的防治

羊膜腔感染是感染相关早产的重要影响因素。羊膜腔感染后炎症引起子宫收缩或伴胎膜早破,导致早产;炎症同时引起胎儿缺氧和死胎。早产儿感染后可发生呼吸窘迫综合征、缺氧缺血性脑病和脑瘫。本文对感染相关早产的发病机制和防治策略进行阐述。     

Relationships between physical abuse during pregnancy and risk factors for preterm birth among women in Manitoba

OBJECTIVE: To describe the prevalence and correlates of physical abuse during the year of pregnancy and to explore the association between physical abuse and other risk factors for preterm birth. DESIGN: Secondary analysis of data from a case-control study of risk factors for preterm birth. SETTING: Two tertiary care hospitals in the Canadian province of Manitoba. PARTICIPANTS: Six hundred eighty postpartum women who delivered a live singleton newborn after spontaneous onset of labor. MAIN OUTCOME MEASURES: Instruments included the Abuse Assessment Screen, Prenatal Psychosocial Profile, Perceived Stress Scale, and a questionnaire to collect data on demographic characteristics, complications during pregnancy, and lifestyle behaviors. RESULTS: Sixty-four women (9.4%) reported being physically abused during the year of pregnancy. Abused women were significantly more likely to be younger, single, of lower income, and less educated than nonabused women. Significant correlates of abuse, after adjusting for other factors in a logistic regression, included the following: illicit drug use, low support from partner, moving two or more times in the past year, high life event stress, bladder infection during pregnancy, Aboriginal race/ethnicity, and single marital status. CONCLUSION: This study suggests that physical abuse during pregnancy is associated with other risk factors for preterm birth, particularly stress and behavioral risk factors such as substance abuse.     

High environmental temperature and preterm birth: A review of the evidence

Objective

to examine the evidence in relation to preterm birth and high environmental temperature.

Background

this review was conducted against a background of global warming and an escalation in the frequency and severity of hot weather together with a rising preterm birth rate.

Methods

electronic health databases such as: SCOPUS, MEDLINE, CINAHL, EMBASE and Maternity and Infant Care were searched for research articles, that examined preterm birth and high environmental temperature. Further searches were based on the reference lists of located articles. Keywords included a search term for preterm birth (preterm birth, preterm, premature, <37 weeks, gestation) and a search term for hot weather (heatwaves, heat-waves, global warming, climate change, extreme heat, hot weather, high temperature, ambient temperature). A total of 159 papers were retrieved in this way. Of these publications, eight met inclusion criteria.

Data extraction

data were extracted and organised under the following headings: study design; dataset and sample; gestational age and effect of environmental heat on preterm birth. Critical Appraisal Skills Programme (CASP) guidelines were used to appraise study quality.

Findings

in this review, the weight of evidence supported an association between high environmental temperature and preterm birth. However, the degree of association varied considerably, and it is not clear what factors influence this relationship. Differing definitions of preterm birth may also add to lack of clarity.

Key conclusions

preterm birth is an increasingly common and debilitating condition that affects a substantial portion of infants. Rates appear to be linked to high environmental temperature, and more especially heat stress, which may be experienced during extreme heat or following a sudden rise in temperature. When this happens, the body may be unable to adapt quickly to the change. As global warming continues, the incidence of high environmental temperature and dramatic temperature changes are also increasing. This situation makes it important that research effort is directed to understanding the degree of association and the mechanism by which high temperature and temperature increases impact on preterm birth. Research is also warranted into the development of more effective cooling practices to ameliorate the effects of heat stress. In the meantime, it is important that pregnant women are advised to take special precautions to avoid heat stress and to keep cool when there are sudden increases in temperature.     

Low first-trimester hemoglobin and low birth weight, preterm birth and small for gestational age newborns.

OBJECTIVE: To examine the relationship between first-trimester hemoglobin (Hb) concentration and risk of low birth weight (LBW), preterm birth and small for gestational age (SGA). METHODS: Data were obtained from a population-based prenatal care program in China. A total of 88,149 women who delivered during 1995-2000 and had their Hb measured in the first trimester were selected as study subjects. RESULTS: The prevalence of anemia (Hb<110 g/L) was 22.1% in the first trimester. The risk of LBW, preterm birth and SGA was increased steadily with the decrease of first-trimester Hb concentration. After controlling for confounding factors, women with Hb 80-99 g/L had significantly higher risk for LBW (OR=1.44, 95% CI 1.17-1.78), preterm birth (OR=1.34, 95% CI 1.16-1.55) and SGA (OR=1.13, 95% CI 0.98-1.31) than women with Hb 100-119 g/L. No elevated risk was noted for women with Hb> or =120 g/L. CONCLUSION: Low first-trimester Hb concentration increases the risk of LBW, preterm birth and SGA.     

Second trimester folate status and preterm birth

OBJECTIVE: The purpose of this study was to show that maternal folate status during pregnancy may be related to preterm birth. STUDY DESIGN: Women were recruited at 24 to 29 weeks' gestation from 1995 to 2000 into the Pregnancy, Infection, and Nutrition Study. Those who completed an interview and a food frequency questionnaire, or provided a blood sample for radioassay of serum (n = 2026) and red blood cell (n = 1034) folate were included. RESULTS: Mean daily dietary folate intake was 463 microg (SD +/- 248). Intake 相似文献   

Predictors of preterm birth.

OBJECTIVE: This is a systematic review to assess published scientific evidence on preterm birth predictors. METHODS: An Internet search for predictors of preterm birth was performed and the evidence level of each method was evaluated. RESULTS: There is strong evidence that preterm birth can be predicted using vaginal sonography to evaluate cervical characteristics, fetal fibronectin in cervicovaginal secretions and interleukin-6 in amniotic fluid. There is consistent evidence that digital cervical examination is a weak predictor, and controversy regarding home uterine activity monitoring. There is scanty evidence about the predictive ability of maternal history and perceptions of symptoms since the study design fails to provide high evidence level. CONCLUSION: Cervical evaluation by vaginal sonography, fetal fibronectin and interleukin-6 are the best methods for predicting preterm birth.     

Leisure time physical activity during pregnancy and preterm birth in Brazil

Objective

To investigate the relationship between leisure time physical activity (LTPA) during pregnancy and preterm birth.

Methods

A cross-sectional, population-based study evaluated LTPA during pregnancy in 4147 mothers using data from the 2004 Pelotas Birth Cohort Study. Gestational age was determined by last menstrual period, or when not available, by ultrasound or the Dubowitz method. Type of LTPA, length of usual session, and frequency were determined for each trimester.

Results

A total of 14.6% of all births were considered preterm. Only 13.3% of women reported engaging in LTPA during pregnancy. After adjusting for confounders, LTPA in all 3 trimesters (prevalence ratio [PR] 0.55; 95% confidence interval [CI] 0.32-0.96), LTPA in the third trimester (PR 0.50; 95% CI 0.31-0.80), and minimum LTPA (≥ 90 min/week) in the third trimester (PR 0.58; 95% CI 0.34-0.98) showed a protective association with preterm birth in the adjusted analysis.

Conclusion

LTPA, especially throughout pregnancy and in the third trimester, was associated with a lower chance of preterm birth.     

Maternal risk factors for preterm birth: a country-based population analysis

Objective

The aim of this study was to identify maternal risk factors for spontaneous preterm birth (PTB) compared to delivery at term, in order to recognize high risk women and to provide a global overview of the Italian situation.

Study design

A multicenter, observational and retrospective, cross-sectional study was designed. The study population comprised 7634 women recruited in 9 different University Maternity Hospitals in Italy. The main criteria for inclusion were: women having had vaginal preterm or term spontaneous delivery in each participating centre during the study period. The records related to deliveries occurring between April and December 2008. A multivariable logistic regression was employed to identify independent predictors of spontaneous preterm birth. Odds ratios (ORs) and 95% confidence intervals (95% CI) were reported with two-tailed probability (p) values. Statistical calculations were carried out using SAS version 9.1. A two-tailed p-value of 0.05 was used to define statistical significant results.

Results

A significant increased risk of PTB was found in women with BMI > 25 (OR = 1.662; 95% CI = 1.033–2.676; p-value = 0.0365) and in women employed in heavy work (OR = 1.947; 95% CI = 1.182–3.207; p-value = 0.0089). Moreover there was a significant association between PTB and previous reproductive history. In fact a history of previous abortion (OR = 1.954; 95% CI = 1.162–3.285; p-value = 0.0116) or previous cesarean section (OR = 2.904; 95% CI = 1.066–7.910; p-value = 0.0371) was positively correlated to the increased risk of PTB and an important statistically significant association was calculated between PTB and previous pre-term delivery (OR = 3.412; 95% CI = 1.342–8.676; p-value = 0.0099). All the other covariates examined as potential risk factors for PTB were not found to be statistically significantly related (p-value > 0.05).

Conclusions

The present study, applied to a substantial sample of Italian population, demonstrates that there are peculiar risk factors for spontaneous PTB in the Italian population examined. It shows an association between preterm delivery and certain maternal factors as: BMI, employment, previous abortions, previous PTBs and previous cesarean section.     

Computer modeling tools to understand the causes of preterm birth

The mechanical integrity of the soft tissue structures supporting the fetus may play a role in maintaining a healthy pregnancy and triggering the onset of labor. Currently, the level of mechanical loading on the uterus, cervix, and fetal membranes during pregnancy is unknown, and it is hypothesized that the over-stretch of these tissues contributes to the premature onset of contractility, tissue remodeling, and membrane rupture, leading to preterm birth. The purpose of this review article is to introduce and discuss engineering analysis tools to evaluate and predict the mechanical loads on the uterus, cervix, and fetal membranes. Here we will explore the potential of using computational biomechanics and finite element analysis to study the causes of preterm birth and to develop a diagnostic tool that can predict gestational outcome. We will define engineering terms and identify the potential engineering variables that could be used to signal an abnormal pregnancy. We will discuss the translational ability of computational models for the better management of clinical patients. We will also discuss the process of model validation and the limitations of these models. We will explore how we can borrow from parallel engineering fields to push the boundary of patient care so that we can work toward eliminating preterm birth.     

The role of depressive symptoms in the pathway of demographic and psychosocial risks to preterm birth and small for gestational age

Objective

depressive symptoms during pregnancy are associated with preterm birth (PTB) and small for gestational age (SGA). Depressive symptoms and PTB and SGA, however, share similar demographic and psychosocial risk factors. Therefore, we investigated whether depressive symptomatology is an independent risk factor, or a mediator in the pathway of demographic and psychosocial risks to PTB and SGA.

Design

multicentre follow-up study.

Participants and setting

pregnant women (n=1013) from midwifery practices, secondary hospitals and a tertiary hospital in three urban areas in the Netherlands.

Measurements

initial risk factors and depressive symptoms were assessed with the Mind2Care instrument, including Edinburgh Depression Scale (EDS) during early pregnancy. Pregnancy outcomes were extracted from medical records. A formal mediation analysis was conducted to investigate the role of depressive symptoms in the pathway to PTB and SGA.

Findings

a univariate association between depressive symptoms and PTB (OR:1.04; 95% CI:1.00–1.08) was observed. After adjusting for the risk factors educational level and smoking in the mediation analysis, this association disappeared. One educational aspect remained associated: low education OR: 1.06; 95%–CI:1.02–1.10.

Key conclusions

depressive symptomatology appeared no mediator in the pathway of demographic and psychosocial risks to PTB or SGA. The presumed association between depressive symptoms and PTB seems spurious and may be explained by demographic and psychosocial risk factors.

Implications for practice

for the prevention of PTB and SGA, interventions directed at demographic and psychosocial risk factors are likely to be of primary concern for clinicians and public health initiatives. As depressive symptoms and PTB and SGA share similar risk factors, both will profit.     

Cervical cerclage for prevention of preterm birth in women with twin pregnancy.

OBJECTIVE: To compare the effect of elective cervical cerclage in women with twin pregnancy on gestational age at time of delivery. METHOD: In a pragmatic fashion women in Abha Maternity Hospital, Saudi Arabia with twin gestations were allocated to receive either an elective cerclage (group I) or no cerclage (group II). Elective cerclage was performed at 12 to 14 weeks of gestation after sonographic examination of the fetus to confirm gestational age and exclude major congenital anomalies. In all cases, follow up of the pregnancy was continued until delivery. RESULTS: Of the 176 twin pregnancies included, cerclage was performed in 76 women, and no cerclage in 100 women. In Group I: 12 pregnancies ended in spontaneous miscarriage, 37 in preterm labor, and 27 women reached full term. There were a total of 106 live births in 62 women. In Group II: 8 women aborted, 44 women ended in preterm labor and 48 women reached full term. There were a total of 160 live births in 89 women. The gestational age at delivery ranged from 20 to 41 weeks. Multiple regression analysis did not show association between cerclage and time of delivery, although a trend was observed (P=0.056). CONCLUSION: Elective cerclage contributes little in prolongation of gestational age at the time of delivery in women with twin pregnancy, especially in women of high parity. Those with a previous history of preterm labor may be a subgroup that could benefit from elective cerclage.     

Additional antibiotic use and preterm birth among bacteriuric and nonbacteriuric pregnant women

OBJECTIVES: To determine the magnitude of and factors associated with spousal abuse during pregnancy in women presenting to tertiary care hospitals in Karachi, Pakistan. METHODS: Five hundred women who delivered a live singleton baby were interviewed. Physical and/or emotional abuse during pregnancy (PEAP) was the primary outcome measure as determined by the World Health Organization's domestic violence module. Frequencies of different forms of abuse were measured and the relationship between PEAP and the risk factors was determined using multiple logistic regression. RESULTS: Of the women interviewed, 44% reported abuse during the index pregnancy; and of these, 43% experienced emotional abuse and 12.6% reported physical abuse. Factors independently associated with PEAP were number of living children (adjusted odds ratio [AOR] 1.34; CI, 1.08-1.65), interfamilial conflicts (AOR 3.03; CI, 1.85-4.96), husband's exposure to maternal abuse (AOR, 2.38; CI, 1.41-4.02), and husband's use of tobacco (AOR 1.59; CI, 1.05-2.42). Women who had adequate social support were less likely to be abused by their husbands (AOR 0.65; CI, 0.51-0.82). CONCLUSIONS: Almost half of the pregnant women interviewed were either physically or emotionally abused. Strong social support helps protect against abuse.     

Progesterone for the prevention of preterm birth: a critical evaluation of evidence

A systematic review of the literature identified nine randomised trials that evaluated the effects of progestational agents in the prevention of preterm delivery. These studies were of variable quality. Meta-analyses showed reductions in delivery rates before 37 weeks (OR 0.42, 95% CI 0.31-0.57) and 34 weeks (OR 0.51, 95% CI 0.34-0.77) as well as in respiratory distress syndrome (OR 0.55, 95% CI 0.31-0.96) with progestational agents. A cumulative meta-analysis showed that the treatment benefit for the outcome of delivery before 37 weeks exceeded the conventional level of statistical significance in 1975 (p<0.01); by 1985, the p-value was <0.001, and by 2003, it was <0.0001. Another cumulative meta-analysis in which the studies were added to the pooled analysis by decreasing quality score showed significant benefit even when the analysis was limited to just the highest quality trials (OR 0.47, 95% CI 0.33, 0.66, p<0.0001). An exploration of the applicability of the effects across various baseline risks using a L'abbe plot found that the benefit was consistent across a range of risks. A comprehensive review of both trial and observational data on harm did not show any demonstrable evidence of harm to mother and baby. Women at high risk of preterm birth should be recommended progestational agent therapy.     

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.     

Risk of preterm delivery in relation to vaginal bleeding in early pregnancy

OBJECTIVE: To examine the relationship between vaginal bleeding during early pregnancy and preterm delivery. METHODS: Study subjects (N=2678) provided information regarding socio-demographic, biomedical, and lifestyle characteristics. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI). RESULTS: Any vaginal bleeding in early pregnancy was associated with a 1.57-fold increased risk of preterm delivery (95% CI: 1.16-2.11). Vaginal bleeding was most strongly related with spontaneous preterm labor (OR=2.10) and weakly associated with preterm premature rupture of membrane (OR=1.36) and medically induced preterm delivery (OR=1.32). As compared to women with no bleeding, those who bled during the first and second trimesters had a 6.24-fold increased risk of spontaneous preterm labor; and 2-3-fold increased risk of medically induced preterm delivery and preterm premature rupture of membrane, respectively. CONCLUSION: Vaginal bleeding, particularly bleeding that persists across the first two trimesters, is associated with an increased risk of preterm delivery.