Work-related physical exertion and risk of preterm, low birthweight delivery

Summary. Although many women work during pregnancy, the effect of maternal job experience on pregnancy outcome is controversial. We investigated whether work-related physical exertion increases a woman's risk of delivering a preterm, low birthweight infant. We studied 773 employed, pregnant women included in the National Longitudinal Survey of Labor Market Experience, Youth Cohort (NLSY), a nationally representative sample of young adults. Data concerning work status, job title during pregnancy, and other factors affecting the outcome of pregnancy were obtained from the NLSY. Assessment of physical exertion was based on job title, using an established catalogue of occupational characteristics. Women in jobs characterised by high physical exertion experienced a higher rate of preterm, low birthweight delivery, defined as maternal report of delivery more than 3 weeks early and birthweight under 2 500 g (adjusted RR=5.1, 95% CI=1.5, 17.7). These findings support a policy of limiting work-related physical exertion during pregnancy.     

Work-related psychosocial stress and risk of preterm, low birthweight delivery.

We investigated whether work-related psychologic stress--defined as work characterized by both high psychologic demands and limited control over the response to these demands--increases a woman's risk of delivering a preterm, low birthweight infant. We studied 786 employed pregnant women included in the National Longitudinal Survey of Labor Market Experience, Youth Cohort (NLSY), a nationally representative sample of 12,686 young adults. Data concerning work status, job title, and other factors affecting pregnancy outcome were obtained from the NLSY. Assessment of job experience was based on job title, using an established catalogue of occupation characteristics. After accounting for the physical exertion entailed in a job, occupational psychologic stress as measured by job title was not associated with preterm, low birthweight delivery for the sample as a whole (Relative risk = 1.16, 95% confidence interval .45, 2.95). For those women who did not want to remain in the work force, work-related stress increased their risk of experiencing this outcome (RR = 8.1, 95% CI 1.5, 50.2). Personal motivation toward work, as well as the physical effort of work, should be considered in evaluating the impact of a job's psychologic characteristics on pregnancy outcome.     

Psychosocial work stress during pregnancy and birthweight

Although there is a growing interest in the health effects of psychosocial work stress, studies on the relationships between job stress and adverse reproductive outcome are limited. We, therefore, investigated the associations between prenatal maternal occupational stress and birthweight using 310 mother-infant pairs included in the Mothers and Children's Environmental Health (MOCEH) study. Information on job stress was collected by interviewing women at enrollment during the first trimester of pregnancy using standardised questionnaires, namely, the Job Content Questionnaire (JCQ) of job strain and effort-reward imbalance (ERI) questionnaires. Regression analyses were carried out. Decision latitude scores of the JCQ were found to be positively related to birthweight, while ERI ratios determined using the ERI model were found to be inversely related to gestational age. In addition, a passive job as defined by the job strain model was found to be associated with a lower birthweight, compared with a relaxed job. These results suggest that work-related psychosocial stress in pregnant women appears to affect birth outcomes, such as birthweight and gestational age.     

Women's physical activity and pregnancy outcome: a longitudinal analysis from the Philippines

We assessed the effects of physical activity on pregnancy outcome in 2741 Filipino women identified during pregnancy as part of a two-year longitudinal study. Specific elements of physical activity hypothesized to be relevant to pregnancy outcome were posture, energy expenditure, and physical stress. Variables were developed for nine household and 48 formal and informal economic activities. Analyses were stratified by whether the woman performed formal waged work outside of the home, income-related activity at home, or was economically inactive. Results show that traditional definitions of physical activity and work based on participation in the formal labour force ignore a sizeable amount of home economic production, as well as the physical demands of housework. We saw no difference in risk of low birthweight or preterm delivery in economically active compared to economically inactive women. However, we found that increased amounts of standing activity affected pregnancy outcome in certain groups of women. Accurate assessment of the effects of physical activity during pregnancy must examine specific components of the activity, rather than relying on formal employment as a proxy for exposure.     

Effects of psychosocial characteristics of work on pregnancy outcomes: a critical review

Birth outcomes may influence subsequent susceptibility to chronic diseases. With the increased number of women who continue to work during pregnancy, occupational stress has been hypothesized to be a potential contributor to adverse reproductive health outcomes. The Job Demand and Control model has been primarily used in investigating associations between work-related stress and outcomes such as preterm delivery, low birth weight, and spontaneous abortion. A literature review of occupational factors that have been associated with adverse reproductive outcomes was conducted. In studies assessing preterm delivery and low birth weight, some evidence has suggested a modest association with work-related stress but has not been conclusive. In the literature on psychosocial characteristics of work and spontaneous abortion, job strain alone was often not associated with adverse outcomes. However the presence of other risk factors resulted in a synergistic effect which strengthened the odds of an adverse outcome. Future studies should use a prospective design with a large study sample, in which work-related stress exposure data are collected before or in the early stages of the pregnancy. In addition, future research should measure psychosocial characteristics of work both objectively and subjectively.     

Partner violence during pregnancy and risk of adverse pregnancy outcomes

The purpose of this cross-sectional study was to investigate the association between partner physical or emotional abuse during pregnancy and pregnancy outcomes including perinatal death, low birthweight and preterm delivery. Women, aged 18-65, who attended one of two large primary care practices from 1997-98 were recruited for this study. Ever pregnant women were asked the frequency of abuse during each pregnancy and details of the pregnancy outcomes. Information regarding abuse during pregnancy and pregnancy outcomes was available for 755 women surveyed who reported a live birth or late fetal death, 14.7% indicated that an intimate partner was violent or abusive toward them during a pregnancy (274 of 1862 pregnancies). Abuse during pregnancy was significantly associated with an increased risk of perinatal death (adjusted relative risk [aRR] = 2.1, 95% confidence interval [CI] 1.3, 3.4) and, among live births, with preterm low birthweight (aRR = 2.4; 95% CI 1.5, 4.0) and term low birthweight (aRR = 1.9; 95% CI 1.0, 3.4). Greater abuse frequency was associated with increased risk. Abuse during pregnancy was associated with perinatal deaths and preterm low birthweight deliveries.     

Characteristics of maternal employment during pregnancy: effects on low birthweight.

BACKGROUND: Although maternal employment is considered a risk factor for low birthweight (LBW), the manner in which employment might affect birthweight is poorly understood. In this analysis, selected characteristics of employment during pregnancy were examined for effects on pregnancy outcomes. METHODS: Work characteristics included the number of hours per week, physical activities, and environmental conditions. The outcomes of interest were fetal growth retardation (less than 2500 grams at term) and preterm delivery (less than 37 weeks). The study population consisted of 2711 non-Black, married mothers who participated in the 1980 National Natality Survey (NNS). The NNS data were merged with data from the 1977 revision of The Dictionary of Occupational Titles (DOT) from which measures of occupational physical activities and environmental exposures were obtained. Logistic regression was used in the analysis. RESULTS: Those who worked 40 or more hours per week were more likely than women who worked fewer hours to have a low birthweight delivery at greater than or equal to 37 weeks. No physical or environmental characterics of work were associated with low birthweight or preterm delivery. CONCLUSIONS: Non-Black married American women may face a risk of delivering low-birthweight babies at or near term only if they work 40 or more hours each week. However, the lack of risk associated with other characteristics of work may be a function of measurement error in the DOT data source or of low levels of exposure in the analysis population.     

Socioeconomic and work related determinants of pregnancy outcome in southern Thailand

STUDY OBJECTIVE: To examine the effect of socioeconomic status on pregnancy outcome in an urbanised area in a rapidly developing country. METHODS: A cohort of 1797 pregnant women who attended antenatal care clinics at the two 700 bed hospitals in Hatyai city was recruited from September 1994 to November 1995. The pregnant women were followed up from the 17th week of gestation until delivery. The socioeconomic indicators selected were family socioeconomic status, maternal education, maternal occupation, family income and work exposure characteristics based upon Karasek's job content questionnaires. Pregnancy outcomes were birth weight, low birth weight, small for gestational age and preterm delivery. MAIN RESULTS: Mean birth weight correlated with socioeconomic status and income but after adjustment for parity, maternal age and height, weight at delivery day, baby sex, obstetrical complications and antenatal care utilisation, only family income remained correlated with birth weight. No association with any socioeconomic status indicators was found when using dichotomous outcome (low birth weight, small for gestational age or preterm delivery). Only high psychological job demand was associated with small for gestational age. Confounder adjustment indicated that the observed social status differences in pregnancy outcomes were mainly attributable to mother's characteristics and antenatal service use. CONCLUSIONS: Socioeconomic indicators alone were not associated with reduced fetal growth or preterm delivery in this study, which recruited mainly lower or middle class women. Karasek's psychological job demand was only weakly correlated with small for gestational age infant.     

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.     

Employment, job strain, and preterm delivery among women in North Carolina.

OBJECTIVES: A population-based case-control study was conducted in central North Carolina to assess the relationship between occupational stress and preterm delivery. METHODS: Four hundred twenty-one women delivering infants before 37 weeks' gestation and 612 women delivering infants at term were interviewed a median of 6 months after delivery. Exposure information was collected for all jobs held for at least 1 month during pregnancy. RESULTS: Work in a "high strain" job (i.e., high demand and low control) was not associated with increased risk of preterm delivery compared with work in "low strain" jobs (all other combinations of job demand and control). Narrowing the exposure window to the third trimester did not modify the results. However, women who worked at a high-strain job full-time (odds ratio [OR] = 1.4, 95% confidence interval [CI] = 0.9, 2.0) or for 30 or more weeks (OR = 1.4, CI = 1.0, 2.2) had a modestly increased risk. Several analyses suggested that Black women were at greater risk from job strain than White women. CONCLUSIONS: This study suggests that chronic exposure during pregnancy to work characterized by high demand and low control may be modestly associated with preterm delivery.     

Vitamin A and carotenoids during pregnancy and maternal, neonatal and infant health outcomes: a systematic review and meta-analysis

Vitamin A (VA) deficiency during pregnancy is common in low-income countries and a growing number of intervention trials have examined the effects of supplementation during pregnancy on maternal, perinatal and infant health outcomes. We systematically reviewed the literature to identify trials isolating the effects of VA or carotenoid supplementation during pregnancy on maternal, fetal, neonatal and early infant health outcomes. Meta-analysis was used to pool effect estimates for outcomes with more than one comparable study. We used GRADE criteria to assess the quality of individual studies and the level of evidence available for each outcome. We identified 23 eligible trials of which 17 had suitable quality for inclusion in meta-analyses. VA or beta-carotene (βC) supplementation during pregnancy did not have a significant overall effect on birthweight indicators, preterm birth, stillbirth, miscarriage or fetal loss. Among HIV-positive women, supplementation was protective against low birthweight (<2.5 kg) [risk ratio (RR) = 0.79 [95% confidence interval (CI) 0.64, 0.99]], but no significant effects on preterm delivery or small-for-gestational age were observed. Pooled analysis of the results of three large randomised trials found no effects of VA supplementation on neonatal/infant mortality, or pregnancy-related maternal mortality (random-effects RR = 0.86 [0.60, 1.24]) although high heterogeneity was observed in the maternal mortality estimate (I(2) = 74%, P = 0.02). VA supplementation during pregnancy was found to improve haemoglobin levels and reduce anaemia risk (<11.0 g/dL) during pregnancy (random-effects RR = 0.81 [0.69, 0.94]), also with high heterogeneity (I(2) = 52%, P = 0.04). We found no effect of VA/βC supplementation on mother-to-child HIV transmission in pooled analysis, although some evidence suggests that it may increase transmission. There is little consistent evidence of benefit of maternal supplementation with VA or βC during pregnancy on maternal or infant mortality. While there may be beneficial effects for certain outcomes, there may also be potential for harm through increased HIV transmission in some populations.     

Population-based study on occupational risk factors for preeclampsia and gestational hypertension

OBJECTIVES: Preeclampsia is a leading cause of maternal and perinatal morbidity. Work-related factors may influence the occurrence of this disorder. This case-control study estimated the associations between work-related physical and psychosocial factors and the risk of preeclampsia and gestational hypertension. METHODS: The eligible women consisted of a random sample of the women who delivered a singleton live birth in 1997-1999 in six regions of Quebec and worked during pregnancy. Cases of preeclampsia (N=102) and gestational hypertension (N=99) were compared with normotensive controls (N=4381). Information on occupational exposures at the onset of pregnancy was collected during phone interviews a few weeks after delivery. Detailed information was obtained on work schedule, postures, physical exertion, work organization, noise, vibration, and extreme temperature. Adjusted odds ratios (aOR) were estimated through polytomous logistic regression. RESULTS: Women standing daily at least 1 hour consecutively without walking experienced a higher risk of preeclampsia [aOR 2.5, 95% confidence interval (95% CI) 1.4-4.6], as well as women climbing stairs frequently (aOR 2.3, 95% CI 1.2-4.1) and women working more than 5 consecutive days without a day-off (aOR 3.0, 95% CI 1.0-9.5). Squatting or kneeling, pushing or pulling objects, whole-body vibration, forced pace, job strain, and no control on breaks were positively, but nonsignificantly, associated with preeclampsia. The associations were weaker for gestational hypertension. CONCLUSIONS: These findings suggest that being exposed to physically demanding and stressful occupational conditions at the onset of pregnancy increases the risk of preeclampsia.     

Pregnancy and its outcome among hospital personnel according to occupation and working conditions.

Relationships between occupation, working conditions, and the development and outcome of pregnancy were analysed on a sample of women employed in hospital during their pregnancy. Ancillary staff members experienced more uterine contractions during pregnancy, more preterm deliveries, and more low birthweight infants than those performing other duties; this remained true after adjusting for social characteristics. The rate of preterm delivery was significantly higher in the presence of at least two of the following arduous working conditions: stand-up work, carrying heavy loads (exclusive of patients), and heavy cleaning tasks; this was so, whatever the occupation.     

Very low birthweight in African American infants: the role of maternal exposure to interpersonal racial discrimination

OBJECTIVES: We determined whether African American women's lifetime exposure to interpersonal racial discrimination is associated with pregnancy outcomes. METHODS: We performed a case-control study among 104 African American women who delivered very low birthweight (<1500 g) preterm (<37 weeks) infants and 208 African American women who delivered non-low-birthweight (>2500 g) term infants in Chicago, Ill. RESULTS: The unadjusted and adjusted odds ratio of very low birthweight infants for maternal lifetime exposure to interpersonal racism in 3 or more domains equaled 3.2 (95% confidence intervals=1.5, 6.6) and 2.6 (1.2, 5.3), respectively. This association tended to persist across maternal sociodemographic, biomedical, and behavioral characteristics. CONCLUSIONS: The lifelong accumulated experiences of racial discrimination by African American women constitute an independent risk factor for preterm delivery.     

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.(ABSTRACT TRUNCATED AT 250 WORDS)     

Preterm delivery and low birthweight among refugees in Greece

Summary. Recently Greece received a large number of refugees mainly from Eastern European countries, Middle East, Africa and the Pontus region. Refugee status, implying psychosocial adversities and financial problems, has traditionally been associated with unfavourable pregnancy outcome. This study aimed to compare the incidence of preterm delivery and low birthweight among 638 refugees and 1231 indigenous women giving birth at the same hospital in Athens. Conditional logistic regression was used in the analysis to account for parity and delivery date (matching variables) as well as controlling explicitly for maternal age and gender of the neonate. It was demonstrated that refugee status did not overall influence the occurrence of preterm delivery or low birthweight, thus implying that these two variables are not sensitive or early indicators of the adverse effects of psychosocial stress suffered by refugees.     

Effect of n-3 long-chain polyunsaturated fatty acid intake during pregnancy on maternal, infant, and child health outcomes: a systematic review

Evidence from observational studies and randomised trials has suggested a potential association between intake of n-3 long-chain polyunsaturated fatty acids (LCPUFA) during pregnancy and certain pregnancy and birth outcomes. Marine foods (e.g. fatty sea fish, algae) and select freshwater fish contain pre-formed n-3 LCPUFA, which serve as precursors for bioactive molecules (e.g. prostaglandins) that influence a variety of biological processes. The main objective of this analysis was to summarise evidence of the effect of n-3 LCPUFA intake during pregnancy on select maternal and child health outcomes. Searches were performed in PubMed, EMBASE, and other electronic databases to identify trials where n-3 LCPUFA were provided to pregnant women for at least one trimester of pregnancy. Data were extracted into a standardised abstraction table and pooled analyses were conducted using RevMan software. Fifteen randomised controlled trials were eligible for inclusion in the meta-analysis, and 14 observational studies were included in the general review. n-3 LCPUFA supplementation during pregnancy resulted in a modest increase in birthweight (mean difference = 42.2 g; [95% CI 14.8, 69.7]) and no significant differences in birth length or head circumference. Women receiving n-3 LCPUFA had a 26% lower risk of early preterm delivery (<34 weeks) (RR = 0.74; [95% CI 0.58, 0.94]) and there was a suggestion of decreased risk of preterm delivery (RR = 0.91; [95% CI 0.82, 1.01]) and low birthweight (RR = 0.92; [95% CI 0.83, 1.02]). n-3 LCPUFA in pregnancy did not influence the occurrence of pre-eclampsia, high blood pressure, infant death, or stillbirth. Our review of observational studies revealed mixed findings, with several large studies reporting positive associations between fish intake and birthweight and several reporting no associations. In conclusion, n-3 LCPUFA supplementation during pregnancy resulted in a decreased risk of early preterm delivery and a modest increase in birthweight. More studies in low- and middle-income countries are needed to determine any effect of n-3 LCPUFA supplementation in resource-poor settings, where n-3 PUFA intake is likely low.     

The contribution of maternal working conditions to socio-economic inequalities in birth outcome

The aims of this study were to examine the association between maternal working conditions and birth outcomes, and to determine the extent to which these contributed to class inequalities in six birth outcomes. We used an existing job exposure matrix developed from survey data collected in 1977 and 1979 to apply occupational-level information on working conditions to the national Swedish Registry, including approximately 280,000 mothers and 360,000 births during the period 1980--1985. Data were analysed using multivariate logistic regressions. Low levels of job control, high levels of physical demands and job hazards were more common in manual compared to non-manual classes. The self-employed had intermediate levels of such exposures. Job exposures, particularly low levels of job control, were generally and significantly associated with higher risks for low birthweight, very low birthweight, small for gestational age, all preterm, very preterm and extremely preterm births, but not with mortality. Compared to middle non-manuals (the reference group), lower non-manual and manual classes had higher risks for all birth outcomes, and these risks were nearly all significant. The highest odds ratios were found for skilled and unskilled manual workers in the manufacturing sector, with ratios between 1.35 and 2.66 (all significant). Job control explained a considerable proportion of inequalities in all birth outcomes. Job hazards contributed particularly to very low birthweight and extremely preterm birth, and physical demands to low birthweight and all preterm births. In conclusion, class differences in maternal working conditions clearly contributed to class differences in low birthweight (explained fraction 14-38%), all preterm births (20-46%), very (14-46%) and extremely (12-100%) preterm births. For very low birthweight and small for gestational age, there was a similar contribution in the manufacturing sector only. For all birth outcomes, class differences could still be detected after working conditions were taken into consideration.     

Reproducibility and validity of maternal recall of pregnancy-related events.

We assessed the reproducibility and validity of a questionnaire that asks mothers to recall pregnancy-related events from thirty or more years ago. Among 146 women who completed the questionnaire twice, responses were highly reproducible for pre-pregnancy height and weight (r = 0.95), pregnancy complications (r = 0.74), substance use (r = 0.80), preterm delivery (r = 0.82), birthweight (r = 0.94), and breastfeeding (r = 0.89). Among 154 women whose questionnaire responses were compared to data collected during their pregnancies, recall was highly accurate for height (r = 0.90), pre-pregnancy weight (r = 0.86), birthweight (r = 0.91), and smoking (sensitivity = 0.86, specificity = 0.94). These findings suggest that long-term maternal recall is both reproducible and accurate for many factors related to pregnancy and delivery.     

Is International or Asian Criteria-based Body Mass Index Associated with Maternal Anaemia,Low Birthweight,and Preterm Births among Thai Population?—An Observational Study

An observational study was conducted in the four southernmost provinces of Thailand aiming at determining the effect of international or Asian criteria-based body mass index (BMI) in predicting maternal anaemia, low birthweight (LBW), and preterm births among pregnant Thai women and the change in haemoglobin (Hb) level during pregnancy. Maternal anaemia was defined as a haemoglobin (Hb) level of <11 g/dL. Anaemia was detected in 27.4% and 26.9% of 1,192 pregnant women at their first prenatal visit and the third trimester respectively. The proportions of overweight and obese women according to the Asian criteria-based pre-pregnancy BMI were higher than the international criteria-based BMI (22.4% and 10.1% vs 15.5% and 3.4% respectively). No significant difference between pre-pregnancy BMI and pregnancy BMI at the first prenatal visit was demonstrated (mean±standard deviation=21.8±4.0 vs 22.8±4.1). Underweight women had a significantly higher prevalence of maternal anaemia, LBW, and preterm birth compared to women with normal weight. Overweight and obese women at pre-pregnancy by the Asian criteria-based BMI had a lower prevalence of anaemia. The Hb levels did not change significantly over time. In addition to BMI, maternal age, parity, and late prenatal visit were independently associated with maternal anaemia, low birthweight, and preterm birth. Underweight pregnant women classified by international or Asian criteria-based BMI increased the risk of maternal anaemia, low birthweight, and preterm birth.Key words: Anaemia, Body mass index, Observational studies, Pregnancy, Thailand