Characteristics of maternal employment during pregnancy: effects on low birthweight

The impact of occupational activities during pregnancy on pregnancy outcomes: a systematic review and metaanalysis

OBJECTIVE

Data: An increasing number of studies suggest that exposure to physically demanding work during pregnancy could be associated with increased risks of adverse pregnancy outcomes, but the results remain conflicted and inconclusive. The purpose of this study was to examine the influence of occupational activities during pregnancy on maternal and fetal health outcomes.

STUDY

Studies of all designs (except case studies and reviews) that contained information on the relevant population (women who engaged in paid work during pregnancy), occupational exposures (heavy lifting, prolonged standing, prolonged walking, prolonged bending, and heavy physical workload), comparator (no exposure to the listed physical work demands), and outcomes (preterm birth, low birthweight, small for gestational age, miscarriage, gestational hypertension, preeclampsia, gestational diabetes mellitus, stillbirth, and intrauterine growth restriction) were included.

STUDY APPRAISAL AND SYNTHESIS METHODS

Five electronic databases and 3 gray literature sources were searched up to March 15, 2019.

RESULTS

Eighty observational studies (N=853,149) were included. Low-to-very low certainty evidence revealed that lifting objects ≥11 kg was associated with an increased odds ratio of miscarriage (odds ratio, 1.31; 95% confidence interval, 1.08-1.58; I²=79%), and preeclampsia (odds ratio, 1.35; 95% confidence interval, 1.07-1.71; I²=0%). Lifting objects for a combined weight of ≥100 kg per day was associated with an increased odds of preterm delivery (odds ratio, 1.31; 95% confidence interval, 1.11-1.56; I²=0%) and having a low birthweight neonate (odds ratio, 2.08; 95% confidence interval, 1.06-4.11; I²=73%). Prolonged standing was associated with increased odds of preterm delivery (odds ratio, 1.11; 95% confidence interval, 1.02-1.22; I²=30%) and having a small-for-gestational-age neonate (odds ratio, 1.17; 95% confidence interval, 1.01-1.35; I²=41%). A heavy physical workload was associated with increased odds of preterm delivery (odds ratio, 1.23; 95% confidence interval, 1.07-1.41; I²=32%) and having a low birthweight neonate (odds ratio, 1.79; 95% confidence interval, 1.11-2.87; I²=87%). All other associations were not statistically significant. Dose-response analysis showed women stand for >2.5 hours per day (vs no standing) had a 10% increase in the odds of having a preterm delivery.

CONCLUSION

Physically demanding work during pregnancy is associated with an increased risk of adverse pregnancy outcomes.

The impact of occupational shift work and working hours during pregnancy on health outcomes: a systematic review and meta-analysis

BACKGROUD

An increasing number of original studies suggest that exposure to shift work and long working hours during pregnancy could be associated with the risk of adverse pregnancy outcomes, but the results remain conflicting and inconclusive.

OBJECTIVE

To examine the influences of shift work and longer working hours during pregnancy on maternal and fetal health outcomes.

DATA SOURCES

Five electronic databases and 3 gray literature sources were searched up to March 15, 2019.

METHODS OF STUDY SELECTION

Studies of all designs (except case studies and reviews) were included, which contained information on the relevant population (women who engaged in paid work during pregnancy); exposure (rotating shift work [shifts change according to a set schedule], fixed night shift [typical working period is between 11:00 pm and 11:00 am] or longer working hours [>40 hours per week]);comparator (fixed day shift [typical working period is between 8:00 am and 6:00 pm] or standard working hours [≤40 hours per week]); and outcomes (preterm delivery, low birthweight [birthweight <2500 g], small for gestational age, miscarriage, gestational hypertension, preeclampsia, intrauterine growth restriction, stillbirth, and gestational diabetes mellitus).

TABULATION, INTEGRATION, AND RESULTS

From 3305 unique citations, 62 observational studies (196,989 women) were included. "Low" to "very low" certainty evidence from these studies revealed that working rotating shifts was associated with an increased odds of preterm delivery (odds ratio, 1.13; 95% confidence interval, 1.00-1.28, I² = 31%), an infant small for gestational age (odds ratio, 1.18, 95% confidence interval, 1.01-1.38, I² = 0%), preeclampsia (odds ratio, 1.75, 95% confidence interval, 1.01-3.01, I² = 75%), and gestational hypertension (odds ratio, 1.19, 95% confidence interval, 1.10-1.29, I² = 0%), compared to those who worked a fixed day shift. Working fixed night shifts was associated with an increased odds of preterm delivery (odds ratio, 1.21; 95% confidence interval, 1.03-1.42; I² = 36%) and miscarriage (odds ratio, 1.23; 95% confidence interval, 1.03-1.47; I² = 37%). Compared with standard hours, working longer hours was associated with an increased odds of miscarriage (odds ratio, 1.38; 95% confidence interval, 1.08-1.77; I² = 73%), preterm delivery (odds ratio, 1.21; 95% confidence interval, 1.11-1.33; I² = 30%), an infant of low birthweight (odds ratio, 1.43; 95% confidence interval, 1.11-1.84; I² = 0%), or an infant small for gestational age (odds ratio, 1.16, 95% confidence interval, 1.00-1.36, I² = 57%). Dose-response analysis showed that women working more than 55.5 hours (vs 40 hours) per week had a 10% increase in the odds of having a preterm delivery.

CONCLUSION

Pregnant women who work rotating shifts, fixed night shifts, or longer hours have an increased risk of adverse pregnancy outcomes.

The impact of maternal employment on children's adiposity: Evidence from China's labor policy reform

BACKGROUND

China has experienced a rapid growth in childhood adiposity in recent years. Although a large number of studies examine the effect of maternal employment on children's adiposity in developed countries, only a few studies investigate the issue in developing countries. Moreover, existing studies tend to suffer from a potential endogeneity issue.

AIMS

We provide new evidence on the causal effect of maternal employment on children's adiposity in China.

MATERIALS AND METHODS

We employ a difference-in-difference strategy that takes advantage of China's 1995 legislative change to labor regulations, which reduced the number of workdays from 6 to 5 days per week. Using longitudinal data from the China Health and Nutrition Survey (CHNS), we compare children whose mothers are wage-earning employees to those whose mothers are self-employed because the reform only affected the former.

RESULTS

Although maternal employment and childhood obesity in China exhibits the same positive association as in the United States, our difference-in-difference estimates present a different picture. We find that a reduction in the maternal labor supply led to children's weight gain. Further investigation reveals that the effect was stronger among children who were male, younger, in urban areas, and from households with low socioeconomic status.

DISCUSSION

Our evidence suggests that a change in maternal behaviors was likely responsible for children's weight gain. In particular, a greater proportion of treatment group mothers cooked and also devoted more time to cooking after the reform, which led to an increased caloric intake by their children. Such weight gain was beneficial for children who were previously underweight but harmful to those who became overweight.

CONCLUSION

The finding implies that additional maternal time at home likely has a different effect in China compared to the United States.

Preterm birth rates in Japan from 1979 to 2014: Analysis of national vital statistics

AIM

Secular trends of preterm birth in Japan between 1979 and 2014 were examined to determine whether changes could be explained by a shift in the distribution of maternal age at delivery and parity and/or by changes in age-specific preterm birth rates.

METHODS

Live birth data for 1979 to 2014 were obtained from the Japanese Ministry of Health, Labour and Welfare. Analyses were limited to singleton children born in Japan (n = 43 632 786). Preterm birth was defined using two cut-offs at < 37 or < 34 weeks of gestation. Crude and standardized rates of preterm birth were calculated for firstborn and later-born singletons by maternal age at delivery for specific time periods.

RESULTS

Throughout the study period, the rates of preterm birth (both at < 37 and < 34 weeks of gestation) were higher among mothers aged 20 and younger, and mid-30s and older, compared to mothers in their 20s or early 30s. The rates of preterm birth at < 37 (but not at < 34) weeks decreased for mothers aged in their late 30s and 40s, and increased for mothers in their 20s and early 30s. Standardized rates of preterm birth showed a secular increase for preterm births at < 37 but not < 34 weeks of gestation.

CONCLUSION

The rates of preterm birth among mothers aged in their 20s and early 30s increased between 1979 and 2014, which contributed to the secular increase in rates of preterm birth at < 37 weeks.

An exploratory spatial analysis to assess the relationship between deprivation, noise and infant mortality: an ecological study

BACKGROUND

Few studies have explored how noise might contribute to social health inequalities, and even fewer have considered infant mortality or its risk factors as the health event of interest.In this paper, we investigate the impact of neighbourhood characteristics - both socio-economic status and ambient noise levels - on the spatial distribution of infant mortality in the Lyon metropolitan area, in France.

METHODS

All infant deaths (n = 715) occurring between 2000 and 2009 were geocoded at census block level. Each census block was assigned multi-component socio-economic characteristics and Lden levels, which measure exposure to noise. Using a spatial-scan statistic, we examined whether there were significant clusters of high risk of infant mortality according to neighbourhood characteristics.

RESULTS

Our results highlight the fact that infant mortality is non-randomly distributed spatially, with clusters of high risk in the south-east of the Lyon metropolitan area (RR = 1.44; p = 0.09). After adjustments for socio-economic characteristics and noise levels, this cluster disappears or shifts according to in line with different scenarios, suggesting that noise and socio-economic characteristics can partially explain the spatial distribution of infant mortality.

CONCLUSION

Our findings show that noise does have an impact on the spatial distribution of mortality after adjustments for socio-economic characteristics. A link between noise and infant mortality seems plausible in view of the three hypothetical, non-exclusive, pathways we propose in our conceptual framework: (i) a psychological pathway, (ii) a physiological disruption process and (iii) an unhealthy behaviours pathway. The lack of studies makes it is difficult to compare our findings with others. They require further research for confirmation and interpretation.

Insulin suppresses ischemic preconditioning-mediated cardioprotection through Akt-dependent mechanisms

It is believed that the diabetic myocardium is refractory to cardioprotection by ischemic preconditioning (IPC) mainly because of impaired insulin signaling to phosphatidylinositol 3-kinase (PI3K) and protein kinase B (PKB or Akt). However, human as well as animal studies have clearly showed that the hearts of type 2 diabetic humans and animals may exhibit increased signaling through PI3K-Akt but yet are resistant to cardioprotection by IPC or ischemic post-conditioning. Therefore, this study was designed to determine whether activation of insulin signaling prior to IPC is detrimental for cardioprotection and to assess the role of insulin receptors (IRs) and Akt in mediating this effect. Wild-type (WT) hearts, hearts lacking IRs or hearts expressing an active form of Akt (myrAkt1) were perfused ex vivo using a Langendorff preparation and were subjected to IPC (3cycles of 5min ischemia followed by 5min reflow before 30min no flow ischemia and then by 45min reperfusion) in the presence or absence of 1nmol/L insulin. Interestingly, whereas insulin was protective against I/R (30min no flow ischemia and 45min reperfusion), it completely abolished cardioprotection by IPC in WT hearts but not in mice lacking insulin receptors (IRs) in cardiomyocytes (CIRKO) or in all cardiac cells (TIRKO). The suppression of IPC-mediated cardioprotection was mediated through downstream signaling to Akt and Gsk3β. In addition, transgenic induction of Akt in the heart was sufficient to abrogate IPC even when insulin was absent, further confirming the involvement of Akt in insulin's suppression of cardioprotection by IPC. These data provide evidence that excessive insulin signaling to Akt is detrimental for cardioprotection by IPC and could explain the failure of the diabetic myocardium to precondition.

Work behaviour during pregnancy in rural China in 2009

OBJECTIVES

To describe the pattern and determinants of working during pregnancy in rural China.

METHODS

A cross-sectional survey was carried out in 2009 in three provinces (Anhui, Chongqing and Shaanxi) in rural China among 3966 mothers who had recently given birth. Multilevel logistic regression was used to examine the determinants of work behaviour during pregnancy.

RESULTS

Overall, 39% of the women stopped working during early pregnancy, 32% worked the same throughout pregnancy and the rest decreased their work or stopped later in pregnancy. Women from Anhui (53%) and Chongqing (54%) provinces were more likely to stop work in early pregnancy than women from Shaanxi province (20%). Older women [odds ratio (OR) 0.74, 95% confidence interval (CI) 0.56-0.99], those having two or more children (OR 0.55, 95% CI 0.43-0.69) and non-farmers (OR 0.50, 95% CI 0.65-0.99) were less likely to stop working on the first trimester, but those with higher education (high school OR 1.43, 95% CI 1.05-1.94) were more likely to stop working. Stopping work early was not related to household income and adequacy of prenatal care. Women with two or more children, non-farmers and those from Shaanxi province were more likely to continue to work to the same extent during pregnancy. But those with higher household income and middle and high school were less likely to work the same.

CONCLUSIONS

Women's working patterns during pregnancy in rural China were polarized: many women stopped working already in early pregnancy, but others continued to work as before. The key determinant of the working patterns was the province of residence.

Work activities and risk of prematurity, low birth weight and pre-eclampsia: an updated review with meta-analysis

OBJECTIVES

We assessed the evidence relating preterm delivery (PTD), low birth weight, small for gestational age (SGA), pre-eclampsia and gestational hypertension to five occupational exposures (working hours, shift work, lifting, standing and physical workload). We conducted a systematic search in Medline and Embase (1966 to 2011), updating a previous search with a further 6 years of observations.

METHODS

As before, combinations of keywords and medical subject headings were used. Each relevant paper was assessed for completeness of reporting and potential for important bias or confounding, and its effect estimates abstracted. Where similar definitions of exposure and outcome existed we calculated pooled estimates of relative risk (RR) in meta-analysis.

RESULTS

Analysis was based on 86 reports (32 cohort investigations, 57 with usable data on PTD, 54 on birth weight and 11 on pre-eclampsia/gestational hypertension); 33 reports were new to this review. For PTD, findings across a substantial evidence base were generally consistent, effectively ruling out large effects (eg, RR>1.2). Larger and higher quality studies were less positive, while meta-estimates of risk were smaller than in previous analyses and best estimates pointed to modest or null effects (RR 1.04 to 1.18). For SGA, the position was similar but meta-estimates were even closer to the null (eight of nine RRs ≤ 1.07). For pre-eclampsia/gestational hypertension the evidence base remains insufficient.

CONCLUSIONS

The balance of evidence is against large effects for the associations investigated. As the evidence base has grown, estimates of risk in relation to these outcomes have become smaller.

The effects of weathering demonstrated by maternal age on low birth weight outcome in babies

BACKGROUND

Increasing age has been hypothesized with wear and tear (weathering) in mothers, which may result to low birthweight of their babies. The prevalence of low birthweight could be heightened if maternal weathering is associated with poor maternal socioeconomic variables. In this current study, we analyzed the effects of maternal weathering on babies' birthweights.

METHODS

One hundred and twenty four mother-baby pairs were selected using systematic random sampling method. Maternal age formed part of the demographic data that was obtained from the mothers' case notes and from interviews held with them. Maternal socioeconomic variables were assessed using Oyedeji's parameters and birthweights of babies were determined using bassinet weighing scale. Associations between maternal socioeconomic variables and birthweight of babies were assessed using univariate analysis. Differences in mean birthweight of babies according to their maternal age were evaluated using one-way analysis of variance ANOVA.

RESULTS

Among the 124 babies, 66(53.2%) were males and 58(46.8%) females of whom the majority 104(83.9%, had normal birthweight. The mean birthweight of babies was 3.05±0.57 (95% CI, 2.95-3.15) kg, while the mean maternal age was 23.60 (5.2) 95% CI, (22.68-24.52) years. The difference between mean birthweight of babies and mean maternal age was not significant (F=1.35, p=0.255). Similarly, the association between birthweight, maternal education and occupation computed using univariate analysis was not significant (F=2.163, p=0.120) for education and (F=1.825, p=0.166) for occupation.

CONCLUSION

In this study, maternal weathering was not found to be associated with LBW outcome. This implies that an increase in maternal age may not be significantly associated with LBW. However, there is need for further research on this subject from different centers using larger sample size in order to enhance the precision of the study.

Reevaluating the relationship between prenatal employment and birth outcomes: a policy-relevant application of propensity score matching

BACKGROUND

Prior research shows an association between prenatal employment characteristics and adverse birth outcomes, but suffers methodological challenges in disentangling women's employment choices from birth outcomes, and little U.S.-based prior research compares outcomes for employed women with those not employed. This study assessed the effect of prenatal employment status on birth outcomes.

METHODS

With data from the Listening to Mothers II survey, conducted among a nationally representative sample of women who delivered a singleton baby in a U.S. hospital in 2005 (n = 1,573), we used propensity score matching to reduce potential selection bias. Primary outcomes were low birth weight (<2,500 g) and preterm birth (gestational age <37 weeks). Exposure was prenatal employment status (full time, part time, not employed). We conducted separate outcomes analyses for each matched cohort using multivariable regression models.

FINDINGS

Comparing full-time employees with women who were not employed, full-time employment was not causally associated with preterm birth (adjusted odds ratio [AOR], 1.37; p = .47) or low birth weight (AOR, 0.73; p = .41). Results were similar comparing full- and part-time workers. Consistent with prior research, Black women, regardless of employment status, had increased odds of low birth weight compared with White women (AOR, 5.07; p = .002).

CONCLUSIONS

Prenatal employment does not independently contribute to preterm births or low birth weight after accounting for characteristics of women with different employment statuses. Efforts to improve birth outcomes should focus on the characteristics of pregnant women (employed or not) that render them vulnerable.

Prenatal care: touching the future

The provision of preconception and prenatal care is a critical and time-honored role for family physicians. It could even be termed the first preventive care a human being receives. It has been suggested by some studies that, because of the continuity of care that is considered a cornerstone of family practice, family physicians provide prenatal care that may improve birth outcome. Although prenatal care is acknowledged as important for a healthy pregnancy and delivery, there is debate regarding the true efficacy of prenatal care.

Physical activity and preterm birth: a literature review

Preterm birth is a major reason for infant mortality and morbidity, representing a public health concern worldwide. Regular and voluntary physical activity is healthy behaviour that should be incorporated by everyone, including pregnant women. On the other hand, some women are exposed to highly demanding occupational physical activities during pregnancy that might represent a threat to the fetus and to their own health. This paper is a literature review of studies (1987-2007) on physical activity during pregnancy and its relationship to preterm birth. Although the effects measured by the studies are not strong and the evidence is impaired by many methodological flaws, it seems that recreational or leisure-time physical activities performed regularly provide protection against prematurity. Studies on occupational physical activities, especially standing for long periods, present contrasting results - some presenting standing as a risk factor, but most showing no association. Housework and other daily activities do not seem to be associated with preterm birth. Regardless of the methodological aspects of the studies reviewed, there is a chance that the real effect of occupational physical activity is being blurred by some underlying factors not easily measured in epidemiological investigations. Our conclusions do not reject the idea that working conditions might represent danger for the pregnancy outcome, but only raise the question that maybe the mechanisms through which employment-related physical activities have been considered up till now could be better and more thoroughly studied. Future studies should pay additional attention to psychological and socioeconomic characteristics, without neglecting biological plausibility.

Physical activity by pregnant women and outcomes for newborns: a systematic review

A systematic review was carried out aiming at analyzing daily physical activity during pregnancy and the outcomes of birth weight, prematurity, and intrauterine growth restriction. Of 52 articles indexed in Medline, 22 that showed better methodological quality were included. Among the 22 articles analyzed, only two did not detect a significant association between physical activity and the outcomes studied. There was large variation between the indicators of maternal physical activity, which included occupational, household, recreational and, all or some, locomotive activities. Among ten articles that measured total daily physical activity, only one article did not find any association. The results support the hypothesis that both excessive and insufficient physical activity impact negatively on pregnancy outcomes.

First-trimester working conditions and birthweight: a prospective cohort study

OBJECTIVES

We investigated the relationship between women's first-trimester working conditions and infant birthweight.

METHODS

Pregnant women (N = 8266) participating in the Amsterdam Born Children and Their Development study completed a questionnaire gathering information on employment and working conditions. After exclusions, 7135 women remained in our analyses. Low birthweight and delivery of a small-for-gestational-age (SGA) infant were the main outcome measures.

RESULTS

After adjustment, a workweek of 32 hours or more (mean birthweight decrease of 43 g) and high job strain (mean birthweight decrease of 72 g) were significantly associated with birthweight. Only high job strain increased the risk of delivering an SGA infant (odds ratio [OR] = 1.5; 95% confidence interval [CI] = 1.1, 2.2). After adjustment, the combination of high job strain and a long workweek resulted in the largest birthweight reduction (150 g) and the highest risk of delivering an SGA infant (OR = 2.0; 95% CI = 1.2, 3.2).

CONCLUSIONS

High levels of job strain during early pregnancy are associated with reduced birthweight and an increased risk of delivering an SGA infant, particularly if mothers work 32 or more hours per week.

Explaining educational inequalities in birthweight: the Generation R Study

Although low socio-economic status has consistently been associated with lower birthweight, little is known about the factors whereby socio-economic disadvantage influences birthweight. We therefore examined explanatory mechanisms that may underlie the association between the educational level of pregnant women, as an indicator of socio-economic status, and birthweight. The study was embedded within a population-based cohort study in the Netherlands. Information on maternal education, offspring's birthweight and several determinants of birthweight was available for 3546 pregnant women of Dutch origin. Infants of the lowest educated women had a statistically significantly lower birthweight than infants of the highest educated women [difference adjusted for gender and gestational age: -123 g (95% CI -167, -79)]. Parity, age of the pregnant women, hypertension, parental height and parental birthweight, marital status, pregnancy planning, financial concerns, number of people in household, weight gain and smoking habits individually explained part of the differences in birthweight, while adjustment for working hours and body mass index resulted in increases in birthweight differences between the educational levels. After full adjustment, the difference in birthweight between lowest and highest education was reduced by 66%. Our study confirmed remarkable educational inequalities in birthweight, a large part of which was explained by pregnancy characteristics, anthropometrics, the psychosocial and material situation, and lifestyle-related factors. Altering smoking habits may be an option to reduce educational differences in birthweight, as many lower-educated women tend to continue smoking during pregnancy. In order to tackle inequalities in birthweight, it is important that interventions are accessible for pregnant women in lower socio-economic strata.

Occupational predictors of pregnancy outcomes in Irish working women in the Lifeways cohort

OBJECTIVE

The objective of this study was to explore the association between occupational factors and pregnancy outcomes in a prospective cohort of Irish pregnant women.

DESIGN

This study has a prospective design.

POPULATION

The Lifeways cohort included 1124 pregnant women, 676 of whom delivered a single baby and were working at their first prenatal care visit when they filled in a self-administered questionnaire.

METHODS

Occupational factors were measured using this questionnaire and included eight factors describing job and working conditions. Data including pregnancy outcomes were also obtained from clinical hospital records. Logistic regression analysis was used to adjust for well-known risk factors.

MAIN OUTCOME MEASURES

Birthweight (< or =3000 g and < or =2500 g), preterm delivery (<37 gestation weeks) and small-for-gestational-age.

RESULTS

Significant associations were found between physical work demands and low birthweight (< or =2500 g) and working with between a temporary contract and preterm delivery. Trends were also observed between working 40 hours or more a week and shift work, and birthweight of 3000 g or less. The study of a cumulative index showed that being exposed to at least two of these occupational factors significantly predicted birthweight of < or =3000 g (OR = 2.44, 95% CI: 1.17-5.08) and of < or =2500 g (OR = 4.65, 95% CI: 1.08-20.07) and preterm delivery (OR = 5.18, 95% CI: 1.00-27.01).

CONCLUSIONS

Our findings suggest that occupational factors may predict birthweight through their predictive effects on preterm delivery. This is one of the few prospective studies on pregnancy outcomes that include working conditions. As they may be modifiable, occupational factors deserve more attention in relation to birth outcomes.

Maternal Work and Birth Outcome Disparities

OBJECTIVES

We tested relations between aspects of maternal work and birth outcomes in a national sample and in subgroups known to experience disparities.

METHODS

Three indices of work attributes (Status and Recognition, Physical Demands, and Exposure to Conflict) were derived by factor analysis of variables extracted from the Department of Labor's O*Net database. The indices were linked to the National Longitudinal Survey of Youth using occupation codes for the primary jobs held by women who gave birth between 1979 and 2000 and worked during the quarter prior to birth (n = 3,386 births to n = 2,508 mothers). Multiple regression was used to model birth outcomes as functions of the work attribute indices, controlling for several measures of socioeconomic status and risk factors for adverse birth outcomes.

RESULTS

In the full sample, work-related Physical Demands were associated with lower average birthweight and increased odds of preterm birth while Status and Recognition was associated with higher average birthweight and lower odds of fetal growth restriction. In stratified models, Status and Recognition was associated with higher birth weight among women with low (versus high) income and with lower odds of preterm birth among women with low (versus high) education. Physical Demands were associated with higher rates of preterm birth among women with low (versus high) income and education and among African-American mothers (compared to Whites).

CONCLUSIONS

The work environment is an important predictor of healthy births. Relations between maternal work attributes and birth outcomes differ by race/ethnicity and socioeconomic status and according to the outcome under investigation. Further research with measures of work attributes specific to maternal work experiences is recommended to confirm our findings.

Risk of prematurity, low birthweight and pre-eclampsia in relation to working hours and physical activities: a systematic review

BACKGROUND

Occupational activities are suspected of having an adverse impact on outcomes of pregnancy.

AIM

To assess the evidence relating three major adverse outcomes (preterm delivery, low birthweight (LBW) and pre-eclampsia/gestational hypertension) to five common occupational exposures (prolonged working hours, shift work, lifting, standing and heavy physical workload).

METHODS

A systematic search of Medline and Embase (1966-December 2005) using combinations of keywords and medical subject heading terms was conducted. For each relevant paper, standard details were abstracted that were then used to summarise the design features of studies, to rate their methodological quality (completeness of reporting and potential for important bias or confounding) and to provide estimates of effect. For studies with similar definitions of exposure and outcome, pooled estimates of relative risk (RR) in meta-analysis were calculated.

RESULTS

53 reports were identified-35 on preterm delivery, 34 on birth weight and 9 on pre-eclampsia or gestational hypertension. These included 21 cohort investigations. For pre-term delivery, extensive evidence relating to each of the exposures of interest was found. Findings were generally consistent and tended to rule out a more than moderate effect size (RR >1.4). The larger and most complete studies were less positive, and pooled estimates of risk pointed to only modest or null effects. For small-for-gestational age, the position was similar, but the evidence base was more limited. For pre-eclampsia and gestational hypertension, it was too small to allow firm conclusions.

CONCLUSIONS

The balance of evidence is not sufficiently compelling to justify mandatory restrictions on any of the activities considered in this review. However, given some uncertainties in the evidence base and the apparent absence of important beneficial effects, it may be prudent to advise against long working hours, prolonged standing and heavy physical work, particularly late in pregnancy. Our review identifies several priorities for future investigation.

Work activity in pregnancy, preventive measures, and the risk of delivering a small-for-gestational-age infant

OBJECTIVES

We undertook a case-control study to evaluate whether some occupational conditions during pregnancy increase the risk of delivering a small-for-gestational-age (SGA) infant and whether taking measures to eliminate these conditions decreases that risk.

METHODS

The 1536 cases and 4441 controls were selected from 43898 women who had single live births between January 1997 and March 1999 in Québec, Canada. The women were interviewed by telephone after delivery.

RESULTS

The risk of having an SGA infant increased with an irregular or shift-work schedule alone and with a cumulative index of the following occupational conditions: night hours, irregular or shift-work schedule, standing, lifting loads, noise, and high psychological demand combined with low social support. When the conditions were not eliminated, the risk increased with the number of conditions (P(trend) =.004; odds ratios=1.00, 1.08, 1.28, 1.43, and 2.29 for 0, 1, 2, 3, and 4-6 conditions, respectively). Elimination of the conditions before 24 weeks of pregnancy brought the risks close to those of unexposed women.

CONCLUSIONS

Certain occupational conditions experienced by pregnant women can increase their risk of having an SGA infant, but preventive measures can reduce the risk.

Socioeconomic factors and low birth weight in Mexico

Background

Low birth weight (LBW) is a public health problem linked to lack of equity in populations. Despite efforts to decrease the proportion of newborns with LBW, success has been quite limited. In recent years, studies focused on explaining how social factors influence this problem have shown that populations with greater inequities have a greater proportion of newborns with LBW.

Methods

The objective was to describe socioeconomic factors related to LBW adjusted by demographic, reproductive and health services variables in Mexico City. A case-control study was carried out in three hospitals with gynaecological and obstetrics services in Mexico City during the first half of 1996. During the recruiting period all children with LBW (cases), defined as newborns weighing <2500 grams, were matched with children born on the same day to control for time of birth. Upon arrival at the hospital for delivery, women were interviewed to determine if they met our inclusion criteria. Women with a history of chronic conditions and those with twin or multiple pregnancies were excluded. Variables with clinical and statistical significance were included in a multivariate model (logistic regression).

Results

We found that low socioeconomic level was the most important risk factor for LBW and was independent of other factors, including those related to reproduction and nutrition, smoking, morbidity during pregnancy, accessibility to health services and prenatal care (OR 2.68; 95% CI 1.19, 6.03).

Conclusion

We found that socioeconomic factors are relevant to LBW. However further research should be done in different population groups as well as developing precise ways of measuring socioeconomic factors and their role in reproductive health.

Impact of maternal age on preterm delivery and low birthweight: a hospital-based collaborative study of nulliparous Lebanese women in Greater Beirut

OBJECTIVES

To analyze the impact of maternal age at first childbirth on the incidence of preterm delivery and low birthweight among single live births delivered to nulliparous Lebanese women in Greater Beirut.

STUDY DESIGN

Eligible subjects were selected from a consecutive sample of neonatal admissions to nine National Collaborative Perinatal Network participating hospitals over a three-year period (April 1, 1999 to March 31, 2002). Chi-square tests and logistic regression analyses were applied.

RESULTS

Out of 5556 nulliparous mothers, 5.4% had a preterm delivery and 5.2% a low-birthweight infant. In the multivariate analysis, preterm delivery was not significantly affected by old maternal age. Mothers aged 25 years or more remained a high-risk group for low birthweight even after controlling for potentially confounding characteristics.

CONCLUSIONS

Maternal age at first childbirth above 25 years is an independent risk factor for low birthweight, but not for preterm delivery, an outcome influenced mainly by obstetric complications.

Prepartum work, job characteristics, and risk of cesarean delivery

BACKGROUND

Reducing the rate of cesarean deliveries in the United States is a high priority among public health officials and members of the medical community. Many factors known to contribute to an individual woman's risk of having a cesarean rather than a vaginal delivery are not readily altered by public policy intervention. In this study we explored the effects on type of delivery of prepartum work practices, a category of factors that has a potential to affect the likelihood of cesarean delivery and to be amenable to change.

METHODS

Data are from U.S. Food and Drug Administration's Infant Feeding Practices Study, using questions on mail surveys administered prenatally and at 1 month postpartum. The sample comprised 1194 women who worked during pregnancy. The outcome measure is type of delivery. Predictor variables are characteristics of prepartum work: how far into their pregnancy the women work, number of hours worked, and occupation.

RESULTS

For most women, maintaining employment through the third trimester, working long hours, and working in certain occupations are not independently associated with the odds of having a cesarean delivery. However, we found marginally significant evidence that those women who worked more than 40 hours a week in a sales job were more likely to have cesarean deliveries than women who worked in other occupations. Conversely, women working part-time in sales jobs were less likely to have a cesarean delivery.

CONCLUSION

This study provides evidence that prenatal work does not substantially increase the probability of having a cesarean delivery in most occupational categories.

Recreational exercise and occupational activity during pregnancy and birth weight: a case-control study

OBJECTIVE

Our purpose was to investigate the impact of exercise and occupational activity on birth weight.

STUDY DESIGN

This case-control study involved singleton infants at > or = 34 weeks' gestation without congenital anomalies. Case subjects had birth weights at <15th percentile for gestational age, and 2 control subjects were selected per case subject. Data were collected by self-completed questionnaire and analyzed by means of logistic regression.

RESULTS

Relative to those who participated in structured exercise 3 or 4 times per week during the third trimester, the odds of lower birth weight were substantially increased for those who exercised > or = 5 times per week (adjusted odds ratio, 4.61; 95% confidence interval, 1.73-12.32) and modestly increased for those at the other extreme, who engaged in structured exercise < or = 2 times per week (adjusted odds ratio, 2.64; 95% confidence interval, 1.29-5.39). Other factors of importance to birth weight were maternal height, prepregnancy body mass, pregnancy weight gain, smoking in the third trimester, and nulliparity.

CONCLUSIONS

Structured exercise frequency during late pregnancy is a determinant of birth weight.

Workplace reproductive problems

Occupational exposures can harm reproductive processes in men or women. Exposures may affect fertility, pregnancy outcomes or the child's health after delivery. The goal of patient management is to provide counseling at an appropriate level. Over-restricting the patient should be avoided while hazardous exposures should be identified and reduced. The occupational history can be used to estimate the magnitude of each exposure. If the exposure is a known reproductive hazard and the exposure level appears significant, there are several options for making the job safer. Modifications in work practices can be accomplished by advising the patient about changing work practices, writing formal work restrictions and talking with the employer. Temporary job transfers may be available. In some cases, a medical leave is needed. The primary care provider can play a key role in assisting patients to reduce reproductive risks.

Stress, pre-term labour and birth outcomes

Stress, pre-term labour and birth outcomes Preliminary studies have suggested that stress may be associated with the onset, treatment and outcomes of pre-term labour; however, a systematic comparison of the stress of women with and without pre-term labour has not been reported. Therefore, the purpose of this exploratory study was to compare the stress (daily hassles and mood states) and birth outcomes of black and white women who experienced pre-term labour (PTL) during pregnancy with those who did not. The convenience sample consisted of 35 pregnant women hospitalized in 1996-1997 for the treatment of PTL (24-35 weeks gestation) and 35 controls matched on age, race, parity, gestational age and method of hospital payment. Women in the PTL group had significantly higher tension-anxiety and depression-dejection on the Profile of Mood States (POMS), lower mean birthweight and mean gestational age, and a higher percentage of babies born <37 weeks and weighing 2500 g or less. Black women in the PTL group and white women in the control group had significantly higher scores on the fatigue sub-scale of the POMS and the work and future security sub-scales of the Daily Hassles Scale. Women in the PTL group whose babies weighed 2500 g or less had significantly higher scores on the health, inner concern and financial responsibility sub-scales of the Daily Hassles Scale. The findings from this study indicate the need for further exploration of the interaction of race and stress in understanding and preventing PTL and low birthweight and the need to examine the role of social support in preventing pre-term birth after an episode of PTL.

Etiology of hearing loss in children. Nongenetic causes

Every child with a hearing loss should have an evaluation to determine the cause of hearing loss. This article focuses on the nongenetic origins of hearing loss, the most frequent of which is the neonatal intensive care unit experience, followed by meningitis, cytomegalovirus, and other infections. Preventable causes such as exposure to ototoxic medications and noise are also discussed in this article.

The effect of heavy maternal workload on fetal growth retardation and preterm delivery. A study among southern Thai women

Heavy maternal workloads are considered to be hazardous to the fetus. The effects of physical activity during pregnancy on low birth weight (LBW), small for gestational age (SGA), and prematurity were assessed from a sample of 1797 women in a follow-up study at the antenatal clinic of two hospitals in southern Thailand. The women were interviewed twice, at 17 and 32 gestational weeks. Outcome data were obtained from medical records and the newborn gestational age determined using Dubowitz's score. The risk of SGA was elevated for women working > 50 hours/week, squatting in work, commuting > 1 hour/day, and having high psychological job demands; the risk of preterm delivery was increased with obstetrical complications. Women who worked long hours and had demanding work conditions had an elevated risk of giving birth to SGA infants but not of preterm delivery.

Effects of maternal work activity during pregnancy on infant malformations

This article examines the association between two birth defects, neural tube defects and oral cleft defects, and maternal physical work demands during the periconceptional period. A case-control study was conducted by comparing exposure characteristics of mothers of malformed infants, as ascertained from the New York State Congenital Malformations Registry (n = 520), with mothers of non-malformed infants (n = 1154). Case groups were further subdivided on whether infants had additional defects. Occupational exposure information was collected from a self-administered questionnaire, and demographic variables from vital records. The results showed no general differences between cases and controls in most variables. However, those infants with cleft defects plus additional defects tended to have a marginally increased risk (odds ratio = 1.76; 95% confidence interval, 1.02-3.21) in relation to maternal jobs requiring standing (> or = 75% of time). We suggest that exposure assessment be improved and defects subdivided for future studies.

Daily demands during pregnancy, gestational age, and birthweight: reviewing physical and psychological demands in employment and non-employment contexts

Although much research has focused on whether the physical demands of employment during pregnancy affect birth outcomes, this article argues that psychological demands should also be considered. Research published since 1980 is reviewed to examine how physical and psychological demands of employment are related to birth outcomes. Evidence for the effect of specific types of physical activities (e.g., lifting, standing) is equivocal, in part due to methodological limitations. However, studies combining several types of physical activities tend to find an association with more adverse birth outcomes. Too few pregnancy outcome studies have examined psychological demands in the workplace to make conclusions about birth outcomes, but the theoretical basis for further research is discussed. This article also argues that physical and psychological demands occur outside of the workplace and must therefore be considered with respect to responsibilities all women face throughout the day. An integrative model for studying these relationships is proposed.

The effects of substance use during gestation on birth outcome, infant and maternal health

This study examines the relationship of substance use to birth outcome, infant, and maternal health in a large, nationally representative sample. Multiple regression analyses, accommodating the nature of the survey data using the SUDAAN software package, indicated that drinking and smoking independently and/or interactively with depression account for poor health and serious medical conditions among pregnant women as well as negative birth outcomes or adverse health consequences in those infants who are live births. In addition, African American women and their infants are more likely than those of other racial groups to suffer these adverse outcomes. Given the risk profiles of individual illnesses, this study suggests the need for developing and targeting health education and preventive efforts specific to those groups that are clearly at greater risk.

Self-reported stress and reproductive health of female lawyers

We studied the prevalence and relationship of stress and working conditions with adverse reproductive outcomes in a cohort of female US law-school alumnae. A total of 584 female lawyers (74% response), aged 25 to 63, responded to a mailed questionnaire. Job hours per week was a strong predictor of job stress. In a logistic regression analysis, women working > 45 hours/week were five times as likely to report high stress as those working < 35 hours/week. Marriage and length of time on the job showed a small inverse association with stress. Women who worked more than 45 hours/week during their first trimester of pregnancy were more likely to report high stress at work during pregnancy. After being adjusted for confounding factors, weekly job hours during the first trimester of pregnancy showed a strong independent association with spontaneous abortion risk (odds ratio [OR], 3.0; 95% confidence interval [CI], 1.4 to 6.6). Seven or more alcohol drinks/week was also independently associated with spontaneous abortion risk (OR, 4.8; 95% CI, 1.5 to 18.1). Self-reported stress during pregnancy was positively but not statistically significantly associated with spontaneous abortion (OR, 1.4; 95% CI 0.8 to 2.3).

Health psychology: what is an unhealthy environment and how does it get under the skin?

This review explores the role of environments in creating chronic and acute health disorders. A general framework for studying the nesting of social environments and the multiple pathways by which environmental factors may adversely affect health is offered. Treating socioeconomic status (SES) and race as contextual factors, we examine characteristics of the environments of community, work, family, and peer interaction for predictors of positive and adverse health outcomes across the lifespan. We consider chronic stress/allostatic load, mental distress, coping skills and resources, and health habits and behaviors as classes of mechanisms that address how unhealthy environments get "under the skin," to create health disorders. Across multiple environments, unhealthy environments are those that threaten safety, that undermine the creation of social ties, and that are conflictual, abusive, or violent. A healthy environment, in contrast, provides safety, opportunities for social integration, and the ability to predict and/or control aspects of that environment.

The cost of poor birth outcomes in employer-sponsored health plans

OBJECTIVES

The authors examine the cost and incidence of poor birth outcomes in employer-sponsored health insurance plans.

METHODS

An extensive study of national inpatient and outpatient claims data for prenatal, delivery, and postnatal care of nearly 59,000 mother-infant pairs was conducted. All maternal and infant costs incurred over a 2-year period were analyzed, and, furthermore, the longitudinal claims experience of a cohort of 20,000 mothers and infants was examined in detail.

RESULTS

The study revealed that 25% of deliveries resulted in poor birth outcomes, which accounted for 40% of total costs over a 2-year period. Extrapolated nationwide, the net direct medical care cost of poor birth outcomes in employer plans has been estimated at approximately $5.6 billion for 1990, approximately 3% of aggregate after-tax corporate profits that year.

CONCLUSIONS

Costs related to maternity and infant care are a major source of cost for employer-sponsored health insurance plans. Poor birth outcomes represent significantly higher cost for both the mother and infant at all stages of care-prenatal, at birth, and postnatal. To the extent that poor birth outcomes relate to maternal behavior and are preventable, their very high and protracted cost may justify substantial health promotion activity by employers and insurers.

Use of public health nursing services: relationship to adequacy of prenatal care and infant outcome

Timing of initial public health nurse contact and number of nurse contacts were examined for their relationship to adequacy of prenatal physician care, infant birthweight, and gestational age. Three historical cohort groups were drawn from three downstate Illinois counties: 1) public health nursing clients (N = 506); 2) Women, Infant, and Children Nutrition Program clients (N = 314); and 3) clients receiving neither of these services (N = 403). Data were obtained from local health department records and a state birth certificate data tape. Descriptive statistics and logistic and multiple regression were used to analyze data. Timing of initial public health contact was significantly correlated to adequacy of prenatal physician contact and infant gestational age. No relationship was found between either timing of initial public health nursing contact or number of these contacts and infant birthweight. The number of public health nursing and physician contacts exerted an additive effect on birthweight and gestational age. Findings lend support for case-finding activities that result in public health nursing contacts early in pregnancy. The importance of multidisciplinary approaches to prenatal care is suggested.

Prenatal care and prevention of preterm birth. A case-control study in southern Spain

The value of prenatal care is controversial and difficult to establish. A national policy for improving perinatal outcomes was proposed and applied throughout Andalusia (Southern Spain) in 1984. Here we report the results of an evaluation of this health care program as regards the prevention of preterm delivery. Effectiveness of prenatal care was assessed on the basis of two case-control studies in a hospital setting: one performed before the program was implemented (1981-1982) and the second one six years after the program began (1990-1993). A total of 229 cases and 395 controls for the period 1981-1982, and 207 cases and 381 controls for 1990-1993 were selected. Prenatal care was assessed based on the number of prenatal care visits, the date of the first visit, and an American composite index adjusting for gestational age. Multiple-factor adjusted odds ratios and their 95% confidence intervals (CI) were estimated using unconditional logistic regression analysis. The use of prenatal care significantly improved across time: the proportion of women receiving no prenatal care decreased from over 30% to less than 5%, and the proportion of women starting prenatal care in the first trimester for 1990-1993 was three times greater than the figure for 1981-1982. In the 1981-1982 case-control study, the date of first visit and the composite index were shown to be unrelated to preterm birth risk; and the number of visits yielded a significant association, although no definite trend could be established. In the 1990-1993 case-control study, a clear and significant relationship was observed between the number of prenatal care visits, the trimester of the first visit, and the adequacy of care according to the composite index. This latter variable, reflecting a more stringent standard of prenatal care, was selected by a stepwise logistic regression analysis as the best predictor for preterm birth risk. The results suggest that the present Andalusian program helps prevent preterm delivery. Nonetheless, its minimum standards should be raised to further decrease preterm birth risk.

The association between occupational factors and preterm birth: a United States nurses' study. Research Committee of the Association of Women's Health, Obstetric, and Neonatal Nurses

OBJECTIVE

Our purpose was to evaluate factors associated with preterm birth among a national sample of U.S. nurses.

STUDY DESIGN

We conducted a case-control study of 210 nurses whose infants were delivered prematurely (< 37 weeks) (cases) and 1260 nurses whose infants were delivered at term (> or = 37 weeks) (controls). An occupational fatigue score was constructed from four sources and varied from 0 to 4. The relation between occupational activity (including hours working and fatigue score) and preterm birth was analyzed with the use of Pearson chi 2 tests, estimates of odds ratios with 95% confidence intervals, and multivariate logistic regression; we controlled for confounding factors.

RESULTS

Factors significantly associated with preterm birth included hours worked per week (p < 0.002), per shift (p < 0.001), and while standing (p < 0.001); noise (p = 0.005); physical exertion (p = 0.01); and occupational fatigue score (p < 0.002). The adjusted odds ratios were 1.6 (p = 0.006) for hours worked per week (< or = 36 vs > 36) and 1.4 (p = 0.02) for fatigue score < 3 vs > or = 3.

CONCLUSIONS

Preterm birth among working women may be related to hours worked per day or week and to adverse working conditions.

Working conditions, maternity legislation, and preterm birth

The review of the scientific literature on the role of employment-related physical activity suggests that prolonged standing and long working hours may increase the risk of preterm delivery. Although maternity legislation in many European countries has regulated work schedules and working conditions for pregnant women, none of the European countries except for France seems to have experienced a reduction in preterm rates. France has had both a comprehensive maternity legislation and a national program specifically aimed to reduce preterm birth. Despite the lack of reduction in preterm rates, paid maternity leave, guaranteed job protection, and regulation of hazardous working conditions remain a desirable societal goal for any industrialized nation.

Employment-related stress and preterm delivery: a contextual examination

Studies of employment-related stress as a risk factor for preterm delivery suggest that contextual factors unrelated to occupation, as well as work-related characteristics, must be examined in assessing this relationship. In this study, the relationship of work and contextual characteristics--assessed at midpregnancy and including scores on an occupational fatigue index--to preterm delivery was examined among 943 black and 425 white low-income multiparous women who were at risk for a poor pregnancy outcome. At 24 to 26 weeks gestational age, a 77-item questionnaire was self-administered to obtain detailed information on sociodemographic and contextual characteristics, home physical activities, and occupational characteristics. Questions in the occupational section of the questionnaire included most of those previously used by Mamelle and coworkers in 1984 and 1987 to construct an occupational fatigue index. The overall preterm delivery rate for black women was 14.0 percent and for white women, 9.6 percent. No relationships were observed between age, education, or marital status and preterm delivery, or between work status, hours per week, transportation, travel time, reliability of child care, or home physical activity and preterm delivery for either black women or white women. Black (but not white) women who continued to work at midpregnancy and who reported being able to take rest breaks when they felt tired had a lower preterm delivery rate (10.4 percent versus 21.9 percent; P = 0.031) compared with those who could or did not. Generally, scores for individual sources and levels of occupational fatigue, as well as total occupational fatigue index scores, were unrelated to preterm delivery in this relatively homogeneous group of low income high-risk women.

Work in pregnancy

Pregnant women in the western world are increasing their part in paid employment. This can be added to their work in the home which, with their leisure and athletic activities, might add up to a considerable load; the possible effects this exertion could have on the woman and her unborn child has been realized only in the last twenty years and many attempts have been made to quantify it. The patterns of work in the home, in employment, and at sporting activity are assessed. There are two distinct areas of possible influence on the fetus: the work with its physical effort might affect respiratory and metabolic acid-base balance and specific teratogens related to activity at work may be encountered and act at nodal points during fetal growth at specific times, causing congenital abnormalities of organs. Potential hazards under chemical, physical, and biological headings are considered, while both the psychological and physical effect of energy expenditure are discussed. Possible measures of outcome are assessed and three recently published studies from the U.S. and U.K. are examined to show the difficulties of making valid measurements about the effect of work on the pregnancy, as well as that of pregnancy on the work. It is probable that ordinary work done by a fit young woman has no serious effect on herself or a healthy fetus. Research will continue, for it may be that with an impaired afferent nutrition and oxygen supply to the fetus, certain specific increases in degrees of work could have an exaggerated effect.

Pregnant women at work: sociodemographic perspectives

The 1988 National Maternal and Infant Health Survey, a stratified random sample of 9,953 live births, shows that women who work during pregnancy are more likely to be non-Hispanic white, married, of higher income and education, to have medical insurance, and of lower parity than nonemployed pregnant women (p < .0001). They begin prenatal care earlier, are less likely to smoke, and are more likely to state that the birth was wanted (p < .0001). Similar trends are seen for full-time as compared to part-time workers. Women employed as precision production workers, operators/fabricators, or in service occupations are disadvantaged with regard to sociodemographic and behavioral risks for pregnancy outcomes relative to women in professional and managerial occupations. Black race, parity, body mass index, and smoking, but not employment, are associated with low birth weight when gestational age is controlled. The effects of stress and its buffers, paternal characteristics, physical activity, and toxic exposures, both in and out of the workplace, should be considered, as should the normative and social policy context.