The associations of parity and maternal age with small-for-gestational-age,preterm, and neonatal and infant mortality: a meta-analysis

Background

Previous studies have reported on adverse neonatal outcomes associated with parity and maternal age. Many of these studies have relied on cross-sectional data, from which drawing causal inference is complex. We explore the associations between parity/maternal age and adverse neonatal outcomes using data from cohort studies conducted in low- and middle-income countries (LMIC).

Methods

Data from 14 cohort studies were included. Parity (nulliparous, parity 1-2, parity ≥3) and maternal age (<18 years, 18-<35 years, ≥35 years) categories were matched with each other to create exposure categories, with those who are parity 1-2 and age 18-<35 years as the reference. Outcomes included small-for-gestational-age (SGA), preterm, neonatal and infant mortality. Adjusted odds ratios (aOR) were calculated per study and meta-analyzed.

Results

Nulliparous, age <18 year women, compared with women who were parity 1-2 and age 18-<35 years had the highest odds of SGA (pooled adjusted OR: 1.80), preterm (pooled aOR: 1.52), neonatal mortality (pooled aOR: 2.07), and infant mortality (pooled aOR: 1.49). Increased odds were also noted for SGA and neonatal mortality for nulliparous/age 18-<35 years, preterm, neonatal, and infant mortality for parity ≥3/age 18-<35 years, and preterm and neonatal mortality for parity ≥3/≥35 years.

Conclusions

Nulliparous women <18 years of age have the highest odds of adverse neonatal outcomes. Family planning has traditionally been the least successful in addressing young age as a risk factor; a renewed focus must be placed on finding effective interventions that delay age at first birth. Higher odds of adverse outcomes are also seen among parity ≥3 / age ≥35 mothers, suggesting that reproductive health interventions need to address the entirety of a woman’s reproductive period.

Funding

Funding was provided by the Bill & Melinda Gates Foundation (810-2054) by a grant to the US Fund for UNICEF to support the activities of the Child Health Epidemiology Reference Group.

     

Medically induced preterm birth and the associations between prenatal care and infant mortality

PurposeDuring the last 30 years, the use of prenatal care, both the proportion of women receiving the recommended number of visits and the average number of visits, has increased substantially. Although infant mortality has decreased, the incidence of preterm birth has increased. We hypothesized that prenatal care may lead to lower infant mortality in part by increasing the detection of obstetrical problems for which the clinical response may be to medically induce preterm birth.MethodsWe examined whether medically induced preterm birth mediates the association between prenatal care and infant mortality by using newly developed methods for mediation analysis. Data are the cohort version of the national linked birth certificate and infant death data for 2003 births. Analyses were adjusted for maternal sociodemographic, geographic, and health characteristics.ResultsReceiving more prenatal care visits than recommended was associated with medically induced preterm birth (odds ratio [OR], 2.44; 95% confidence interval [95% CI], 2.40–2.49) compared with fewer visits than recommended). Medically induced preterm birth was itself associated with greater infant mortality (OR, 5.08; 95% CI, 4.61–5.60) but that association was weaker among women receiving extra prenatal care visits (OR 3.08; 95% CI, 2.88–3.30) compared with women receiving the recommended number of visits or fewer.ConclusionsThese analyses suggest that some of the benefit of prenatal care in terms of infant mortality may be in part due to medically induced preterm birth. If so, the use of preterm birth rates as a metric for tracking birth policy and outcomes could be misleading.     

Socioeconomic domains and associations with preterm birth

Neighborhood socioeconomic effects on health have been estimated using multiple variables and indices. This inconsistent estimation approach makes comparison across geographic areas challenging. In this paper, we developed indices representing specific socioeconomic domains that can be reproduced in other areas to estimate elements of the neighborhood socioeconomic environment on health outcomes, specifically preterm birth. Using year 2000 U.S. census data and principal components analysis, socioeconomic indices were developed representing a priori - defined domains of education, employment, housing, occupation, poverty and residential stability. These socioeconomic indices were subsequently used in race-stratified multilevel logistic regression models of preterm birth in eight socioeconomically distinct study areas in the U.S. Maternal residence was obtained from birth records and was geocoded to census tracts. In maternal age and education adjusted models, living in tracts with high unemployment, low education, poor housing, low proportion of managerial or professional occupation and high poverty was associated with increased odds of preterm birth for non-Hispanic white women at most sites. Among non-Hispanic black women, similar associations were noted for tract-level low education, high unemployment, low occupation, and high poverty, but the effect estimates were generally smaller than those seen for white women. Increasing amounts of residential stability were not associated with preterm birth in these analyses. We combined the domain estimates across the eight study sites to produce pooled effect estimates for the socioeconomic domains on preterm birth. The research reported here suggests that specific neighborhood-level socioeconomic features may be especially influential to health outcomes. These socioeconomic domains represent potential targets for intervention or policy efforts designed to improve maternal and child health and reduce health disparities.     

A comparison of four prenatal care indices in birth outcome models: comparable results for predicting small-for-gestational-age outcome but different results for preterm birth or infant mortality

ObjectiveSeveral different indices of prenatal care have been used in birth outcome models to analyze the relationship between the adequacy of prenatal care and low birthweight, preterm birth, and infant mortality. This investigation compared the performance of the Kessner index, the GINDEX, the adequacy of prenatal care utilization (APNCU) and certain variants of the APNCU in such outcome models.Study Design and SettingData from National Center for Health Statistics' (NCHS) Linked Birth and Infant Death Cohort files were used in multivariate logistic regression models to estimate adjusted odds ratios comparing different prenatal care utilization categories for each index.ResultsWhen the indices were used in small-for-gestational-age outcome models, the conclusions suggested by the various indices were similar. In models for preterm birth and infant mortality, by contrast, the various indices gave widely differing results. Unlike the use of other indices, the use of the GINDEX paradoxically suggested that birth outcomes were better in the inadequate, intermediate, and intensive categories than in the adequate category.ConclusionThe conclusions drawn concerning the association between prenatal care utilization and small-for-gestational-age seem relatively robust in the sense of being consistent across indices. In analyzing associations between prenatal care and preterm birth or infant mortality, care must be taken in choosing indices, because results differ substantially across indices.     

Maternal levels of polychlorinated biphenyls in relation to preterm and small-for-gestational-age birth

BACKGROUND: In developed countries, polychlorinated biphenyls (PCBs) are ubiquitous contaminants of the environment, including foods. Within the range of the resulting low-level exposure, associations of PCBs with lower birth weight have been observed in several studies. METHODS: To examine further the association of PCBs with birth outcomes, we measured serum levels in 1034 pregnant women who were enrolled in the U.S. Collaborative Perinatal Project in 1959 to 1965 before PCB manufacturing was banned. RESULTS: The multivariate-adjusted odds ratio for preterm birth among those with PCB levels of >/=4 microg/L of total PCBs, compared with those with <2 microg/L, was 1.1 (95% confidence interval = 0.6-2.2); for the same exposure contrast, the odds ratio for delivering an infant who was small-for-gestational-age at birth was 1.6 (0.7-3.7). Birth weight and length of gestation were essentially unrelated to PCB level. CONCLUSIONS: In these data, maternal levels of PCBs during pregnancy were essentially unrelated to preterm birth, birth weight, or length of gestation. An association of PCBs with small-for-gestational-age birth was observed, but the results were inconclusive and occurred in the absence of an overall decrease in birth weight.     

Fetal growth, preterm birth and infant mortality in relation to work with video display terminals during pregnancy.

Through register linkage between a trade union file and public health registers 24,352 pregnancy outcomes were selected from a source population of 214,108 commercial and clerical employees. In a case-base study including all recorded cases and a randomly selected base sample, the potential effect of video display terminal (VDT) use in pregnancy on the risk of low birthweight, preterm birth, light weight for delivery date, stillborn, perinatal death, and infant death was investigated. Data on VDT use and potential confounders were collected from postal questionnaires sent to 6312 women and 426 employers. The rate ratio for women exposed to any degree of use was 0.88 for low birthweight [95% confidence interval (95% CI) 0.67-1.16], 1.11 for preterm birth (95% CI 0.87-1.47), 0.99 for light weight for delivery date (95% CI 0.80-1.21), 0.73 for stillborn (95% CI 0.36-1.48), 1.10 for perinatal death (95% CI 0.62-1.94), and 0.20 for infant death (95% CI 0.04-1.03). In conclusion, this investigation did not show an increased risk of the studied adverse pregnancy outcomes among women with VDT use.     

Shift work,long working hours and preterm birth: a systematic review and meta-analysis

Purpose

Specific physical activities or working conditions are suspected for increasing the risk of preterm birth (PTB). The aim of this meta-analysis is to review and summarize the pre-existing evidence on the effect of shift work or long working hours on the risk of PTB.

Methods

We conducted a systematic search in MEDLINE and EMBASE (1990–2013) for observational and intervention studies with original data. We only included articles that met our specific criteria for language, exposure, outcome, data collection and original data that were of at least of moderate quality. The data of the included studies were pooled.

Results

Eight high-quality studies and eight moderate-quality studies were included in the meta-analysis. In these studies, no clear or statistically significant relationship between shift work and PTB was found. The summary estimate OR for performing shift work during pregnancy and the risk of PTB were 1.04 (95 % CI 0.90–1.20). For long working hours during pregnancy, the summary estimate OR was 1.25 (95 % CI 1.01–1.54), indicating a marginally statistically significant relationship but an only slightly elevated risk.

Conclusion

Although in many of the included studies a positive association between long working hours and PTB was seen this did reach only marginal statistical significance. In the studies included in this review, working in shifts or in night shifts during pregnancy was not significantly associated with an increased risk for PTB. For both risk factors, due to the lack of high-quality studies focusing on the risks per trimester, in particular the third trimester, a firm conclusion about an association cannot be stated.     

宁海县2010—2015年5岁以下儿童死亡原因分析

目的探讨妊娠中期(孕24~28周)无症状孕妇血清IL-1、IL-6、IL-8、TNF-a及CRH浓度与早产的关系。方法选择2015年1月—2017年12月在上海市浦东新区妇幼保健院定期产检,孕24~28周无症状的孕妇,抽取其静脉血,采样冻存待测。随访其妊娠结局,根据妊娠结局选择早产组100例,包括自发性早产71例和未足月胎膜早破29例,并选择同期足月分娩者100例为对照组。采用ELISA法检测血清IL-1、IL-6、IL-8、TNF-a和CRH的浓度。两组产后胎膜送病理检查,判断有无绒毛膜羊膜炎。结果早产组孕24~28周血清IL-1、IL-6、IL-8浓度高于对照组(P < 0.05), 血清TNF-a、CRH浓度无明显升高(P>0.05)。早产绒毛膜羊膜炎组血清IL-6、IL-8浓度高于早产非绒毛膜羊膜炎组和对照组,早产非绒毛膜羊膜炎组和对照组差异无统计学意义(P < 0.05);早产绒毛膜羊膜炎组的血清IL-1浓度与早产非绒毛膜羊膜炎组比较,差异无统计学意义,但明显高于对照组(P < 0.05)。3组间血清TNF-a和CRH的浓度差异无统计学意义(P>0.05)。血清IL-1预测早产的ROC曲线下面积(AUC)为0.843,最佳界值为10.699 pg/mL;IL-6的AUC为0.675,最佳界值为104.411 pg/mL;IL-8的AUC为0.55,最佳界值为65.496 pg/mL。结论孕24~28周无症状孕妇的血清IL-1、IL-6、IL-8水平对预测早产有一定的价值。     

孕期增重与早产关联的流行病学分析

妊娠期孕妇的睡眠模式发生明显改变,睡眠时间异常、睡眠质量差等问题尤为突出。不健康的睡眠模式增加了不良妊娠结局的发生风险,早产作为最常见的不良妊娠结局,是导致新生儿患病和死亡的最主要原因。笔者通过文献复习,对孕妇睡眠现状进行简述,同时从睡眠时间和睡眠质量2个方面概述睡眠与早产之间的关系。在未来研究中,应加强对孕妇睡眠情况的关注,制定有效的干预措施,指导孕妇进行健康睡眠。     

The worldwide incidence of preterm birth: a systematic review of maternal mortality and morbidity

Objective

To analyse preterm birth rates worldwide to assess the incidence of this public health problem, map the regional distribution of preterm births and gain insight into existing assessment strategies.

Methods

Data on preterm birth rates worldwide were extracted during a previous systematic review of published and unpublished data on maternal mortality and morbidity reported between 1997 and 2002. Those data were supplemented through a complementary search covering the period 2003–2007. Region-specific multiple regression models were used to estimate the preterm birth rates for countries with no data.

Findings

We estimated that in 2005, 12.9 million births, or 9.6% of all births worldwide, were preterm. Approximately 11 million (85%) of these preterm births were concentrated in Africa and Asia, while about 0.5 million occurred in each of Europe and North America (excluding Mexico) and 0.9 million in Latin America and the Caribbean. The highest rates of preterm birth were in Africa and North America (11.9% and 10.6% of all births, respectively), and the lowest were in Europe (6.2%).

Conclusion

Preterm birth is an important perinatal health problem across the globe. Developing countries, especially those in Africa and southern Asia, incur the highest burden in terms of absolute numbers, although a high rate is also observed in North America. A better understanding of the causes of preterm birth and improved estimates of the incidence of preterm birth at the country level are needed to improve access to effective obstetric and neonatal care.     

Pregnancy intention and preterm birth: differential associations among a diverse population of women

CONTEXT: Studies published to date provide mixed evidence on the relationship between unintended pregnancy and preterm birth, and none take into consideration that the meaning of unintended pregnancy may vary across racial and ethnic groups. METHODS: Data from the 1999-2003 rounds of the Maternal and Infant Health Assessment, a population-based, representative survey of postpartum women in California, were used to assess the relationship between pregnancy intention and preterm birth. For racial and ethnic groups in which an association was found, sequential logistic regression was conducted to further examine the relationship while controlling for socioeconomic characteristics. RESULTS: In unadjusted results, pregnancy intention was associated with preterm birth among both whites and immigrant Latinas, but not among blacks or U.S.-born Latinas. Among whites, compared with women who reported that their pregnancy was intended, those who were unsure about their pregnancy had elevated odds of preterm birth (odds ratio, 1.4), as did those who reported their pregnancy was unwanted (1.7) or mistimed (1.4). Among immigrant Latinas, those who reported being unsure about their pregnancy were at higher risk of preterm birth than were those who reported an intended pregnancy (1.6). After adjustment for socioeconomic factors, the association remained significant for immigrant Latinas who were unsure about their pregnancy (1.5), but none of the associations remained significant for whites. CONCLUSIONS: Women's interpretations of questions about pregnancy intention and their social experiences regarding pregnancy intention may vary by race or ethnicity. Studies on the association between pregnancy intention and preterm birth may need to be group-specific.     

Atrazine in municipal drinking water and risk of low birth weight, preterm delivery, and small-for-gestational-age status

Background: Atrazine is a herbicide used extensively worldwide. Bioassays have shown that it is embryotoxic and embryolethal. Evidence of adverse reproductive outcomes from exposure in the general population is sparse.

Aims: To evaluate the association between atrazine levels in municipal drinking water and the following adverse reproductive outcomes: increased risk of preterm delivery, low birth weight (LBW), and small-for-gestational-age (SGA) status.

Methods: A total of 3510 births that took place from 1 October 1997, to 30 September 1998 were analysed. Atrazine measurements were available for 2661 samples from water treatment plants over the past decade. A seasonal pattern was identified, with atrazine peaking from May to September. The geometric mean of the atrazine level for this period was calculated for each water distribution unit and merged with the individual data by municipality of residence.

Results: Atrazine levels in water were not associated with an increased risk of LBW or SGA status and were slightly associated with prematurity. There was an increased risk of SGA status in cases in which the third trimester overlapped in whole or in part with the May–September period, compared with those in which the third trimester occurred totally from October to April (OR = 1.37, 95% CI 1.04 to 1.81). If the entire third trimester took place from May to September, the OR was 1.54 (95% CI 1.11 to 2.13).

Conclusions: Low levels of atrazine, a narrow exposure range, and limitations in the exposure assessment partly explain the lack of associations with atrazine. Findings point to the third trimester of pregnancy as the potential vulnerable period for an increased risk of SGA birth. Exposures other than atrazine and also seasonal factors may explain the increased risk.

     

Population exposures to I-131 releases from Hanford Nuclear Reservation and preterm birth,infant mortality,and fetal deaths

Communities surrounding the Hanford Nuclear Reservation in southeastern Washington were exposed to radionuclides, particularly iodine-131, released during the period 1945 to 1951. This study evaluated whether estimated iodine-131 exposures were risk factors for infant mortality, fetal death, and preterm birth in the years of highest releases, 1945 and 1946. Data on births, fetal deaths, and infant deaths, during the period 1940 to 1950, were abstracted from vital records for an eight county area surrounding the Hanford facility. The analysis included 56,320 births, 1,656 infant deaths, and 806 fetal deaths. The Hanford Environmental Dose Reconstruction project provided iodine-131 dose estimates for the 1,102 grid areas in the study area. The grid areas were collapsed into 4 exposure groups using estimated exposure to iodine-131 during 1945. Each birth and death record was assigned to one of the four grid groups based on mother's residence at the time of birth. Comparisons of preterm birth, infant death, and fetal death rates were made among the grid groupings for the primary exposure period (1945 to 1946) and for other years of the study period (i.e., 1940 to 1944 and 1947 to 1950). In the grid group with the highest estimated iodine-131 exposures, the mother's residence during the latter part of pregnancy was associated with preterm birth (OR = 1.74, 95% CI = 1.09-2.72). An association with infant mortality (OR = 1.26, 95% CI = 0.79-1.97) was suggested. No association was found for fetal deaths. This study found that iodine-131 exposure was associated with increased risk of preterm birth. This finding is biologically plausible because other studies have found that: (1) iodine-131 exposure can cause hypothyroidism, and (2) overt or subclinical hypothyroidism during pregnancy can increase a mother's risk of a preterm delivery.     

The infant mortality rate, life expectancy at birth, and a linear index of mortality as measures of general health status

The infant mortality rate is not a good indicator of overall mortality or health status. Based on new empirical life tables from the UN Population Division, it can only predict life expectancy with 95% confidence to within a 14-year range. Two infant mortality rates must be nearly 80 units apart to be 95% confident that life expectancy in the two communities is different. Life expectancy itself is not an ideal general measure of mortality, because it implicitly weights deaths at different ages in an inconsistent fashion. A measure of potential years of life lost is preferable because it is ethically more consistent.