Heavy physical work during pregnancy--a risk factor for small-for-gestational-age babies in Poland

Night work during pregnancy and small for gestational age: a Danish nationwide register-based cohort study

OBJECTIVE

The aim was to investigate the association between night work during pregnancy and risk of having a small for gestational age (SGA) child.

METHODS

This cohort study had payroll data with detailed information on working hours for employees in all Danish administrative regions (primarily hospital employees) between 2007 and 2015, retrieved from the Danish Working Hour Database. Pregnancies, covariates and outcome were identified from the national birth registry. We used logistic regression to investigate the association between intensity and duration of night work during the first 32 pregnancy weeks and SGA. The adjusted model included age, body mass index, socioeconomic status and smoking. Using quantitative bias analysis and G-estimation, we explored potential healthy worker survivor bias (HWSB).

RESULTS

The final cohort comprised 24 548 singleton pregnancies in 19 107 women, primarily nurses and medical doctors. None of the dimensions of night work were associated with an increased risk of SGA. We found a tendency towards higher risk of SGA in pregnancies where the women stopped having night shifts during pregnancy. Using G-estimation we found an OR<1 for the association between night work and SGA if all workers continued having night work during pregnancy compared with daywork only.

CONCLUSION

We found no increased risk of SGA in association with night work during pregnancy among healthcare workers. G-estimation was not precise enough to estimate the observed indication of HWSB. We need better data on pregnancy discomforts and complications to be able to safely rule out HWSB.

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.

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.

Shift work and pregnancy outcomes: a systematic review with meta-analysis of currently available epidemiological studies

BACKGROUND

Varying work schedules are suspected of increasing risks to pregnant women and to fetal wellbeing. In particular, maternal hormonal disturbance arising from sleep deprivation or circadian rhythm disruption might impair fetal growth or lead to complications of pregnancy. Two independent meta-analyses (from 2000 to 2007) reported a small adverse effect of shift work on the risk of preterm delivery (PTD). However, these reviews were based on few high-quality studies.

OBJECTIVES

To provide an updated review of the associations of shift work with PTD, low birthweight (LBW), small-for-gestational-age (SGA) infants and pre-eclampsia.

SEARCH STRATEGY AND SELECTION CRITERIA

We conducted a systematic search of MEDLINE using combinations of keywords and MeSH terms.

DATA COLLECTION AND ANALYSIS

For each relevant paper we abstracted standard details, used to summarise design features and rate methodological quality. We calculated pooled estimates of relative risk (RR) in random-effect meta-analyses.

MAIN RESULTS

We retrieved 23 relevant studies. The pooled estimate of RR for PTD was 1.16 (95% CI 1.00-1.33, 16 studies), but when five reports of poorer methodological quality were excluded, the estimated RR decreased to 1.03 (95% CI 0.93-1.14). We also observed increased RRs for LBW (RR 1.27, 95% CI 0.93-1.74) and for SGA (RR 1.12, 95% CI 1.03-1.22), which varied little by study quality. Little evidence was found on pre-eclampsia.

CONCLUSIONS

These findings suggest that overall, any risk of PTD, LBW, or SGA arising from shift work in pregnancy is small.

Work as a nurse and a midwife and adverse pregnancy outcomes: a Finnish nationwide population-based study

OBJECTIVE

To assess whether work as a nurse and a midwife during pregnancy increases the risk of adverse pregnancy outcomes.

METHODS

We identified from the 1990-2006 Finnish Medical Birth Registry all singleton births to nurses (n=109,542), midwives (n=3,009), and teachers (n=23,454) (referents). The main outcomes were sexual differentiation, low and high birth weight, preterm and postterm delivery, small and large for gestational age, and perinatal death.

RESULTS

The prevalence of low birth weight (2.9% vs. 2.5%), preterm delivery (4.4% vs. 4.1%), postterm delivery (4.7% vs. 4.1%), small for gestational age (1.8% vs. 1.4%), perinatal death (0.45% vs. 0.41%) and stillbirth (0.30% vs. 0.25%) was higher among the newborns of nurses than those of teachers. The adjusted odds ratio (OR) from generalized estimating equations was 1.17 (95% confidence interval [CI] 1.07-1.26) for low birth weight, 1.09 (95% CI 1.02-1.16) for preterm delivery, 1.11 (95% CI 1.03-1.18) for postterm delivery, 1.17 (95% CI 1.05-1.30) for small for gestational age, 1.12 (95% CI 0.90-1.35) for perinatal death, and 1.27 (95% CI 0.98-1.56) for stillbirth. For midwives, the risk of small for gestational age (OR=1.25, 95% CI 0.95-1.55) was elevated, but the 95% CI included unity. There was no substantial difference in the sex distribution.

CONCLUSIONS

This study provides evidence that work as a nurse may reduce fetal growth and duration of pregnancy. The inference is based on the newborns of teachers as the reference group. However, the prevalence of most of the outcomes was higher among the newborns of all other working women combined than in the newborns of both nurses and teachers.

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.

Association of maternal work with adverse perinatal outcome

OBJECTIVE

To investigate the relationship between maternal work and pregnancy outcome.

METHODS

Over a 4-month period from October 2004 through February 2005, 2,419 women were interviewed shortly after delivery in the three main public and Health Insurance hospitals in Alexandria, Egypt. Of these, 730 (30.2%) were working and 1,689 (69.8%) were not working prior to delivery. A detailed description of working status was analyzed, along with a risk profile which was compared between the two groups.

RESULTS

There was no significant association between different work characteristics and perinatal outcomes except for that between working posture, stress and delivery of small-for-gestational-age (SGA) babies. There was an excess rate of SGA and perinatal death among the non-working group, while preterm delivery was significantly increased among those who worked throughout the whole pregnancy. After adjusting for confounders, the risk of preterm delivery was no longer significant (OR = 1.2, 95% CI = 0.96-1.7). On the other hand, working status had a beneficial effect on SGA and perinatal death (OR = 0.41, 95% CI = 0.26-0.64 and OR = 0.26, 95% CI = 0.14-0.48, respectively).

CONCLUSION

These results cast doubt on the risk of adverse pregnancy outcome for women who work during pregnancy. Work per se does not constitute a health risk factor and may even have a positive social impact on pregnancy. Further research on this topic in our region is recommended.

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.

Analysis of self-reported problematic tasks for pregnant women

The objective of this study was to identify major components of, and influential factors in, problematic tasks performed by pregnant women employed in education, health care and service areas. Seventy-two pregnant women were surveyed using specially designed questionnaires consisting of an Initial Survey, a Job Analysis Questionnaire and a Task Description Questionnaire. Forty-four subjects (60%) had difficulty performing at least one work task and reported 105 tasks that were problematic at work. Reaching above the head, bending forward, bending and twisting, pushing, repeating actions and working at a fast pace were identified as the task components requiring the greatest level of effort. Excessive effort, excessive time, getting tired, repetitive actions, stress and fear of injury were identified as factors that had strong associations with the six major task components. Findings of this study suggest that these task components and factors should be considered when designing, assigning or analysing tasks for working pregnant women.

Exposure to pesticides and heavy work in greenhouses during pregnancy: does it effect birth weight?

OBJECTIVES

Work in greenhouses is performed in warm microclimate during the most time of the year, involves usually moderately intense or heavy work. The working conditions in greenhouses might involve also indirect exposure to pesticides resulting from contact with pesticide-treated flowers and vegetables. The aim of the study was to investigate whether the work in greenhouse during pregnancy adversely influenced infant birth weight and, if so, which of the two main potential hazards typical for such environment (heavy physical work or exposure to pesticides) played the major role in this process.

METHODS

The list of 14 major greenhouses (each above 5 ha) growing vegetables (cucumbers and tomatoes) was obtained from the Polish Chamber of Horticulture. Between January 2001 and December 2003, 460 women at the age below 45 years, married or who lived with a partner and who had been working for a period of at least 2 years in greenhouses in Poland were asked to participate in the project. We classified pregnancies of women working in, and out of, greenhouses on the basis of energy expenditure during mother's work into three groups: A (200-700 kcal/shift); B (701-1000 kcal/shift); and C (1001-1200 kcal/shift). Information about application of pesticides in 1997-2001 was received from persons responsible for chemical protection in each examined greenhouse. Trade names of pesticides, names and amounts of the active ingredients, type of cultivation and its area were abstracted from pesticide application registers run by each greenhouse operator. Pesticides were classified as reproductive and developmental (RD) toxins according to Pan American Pesticide Database classification.

RESULTS

The mean birth weight of infants whose mothers worked in greenhouse during pregnancy (work expenditure >1000 kcal/shift) was 177 g lower than that of those whose mothers worked out of greenhouse (light work <700 kcal/shift) (p = 0.05). Mothers who during work in greenhouse were potentially exposed to RD pesticides, delivered infants with birth weight lower by about 70 g. than infants' mothers not working at places where pesticides RD were applied, but these findings were not statistically significant.

CONCLUSION

Our results indicate that infants of mothers performing heavy work inside greenhouse during pregnancy had lower mean birth weight than infants of mothers working out of greenhouse. No similar effects of current exposure to pesticides was observed.

Risk factors for low birth weight: a review

Low birth weight (LBW) is one of the main predictors of infant mortality. The global incidence of LBW is around 17%, although estimates vary from 19% in the developing countries (countries where it is an important public health problem) to 5-7% in the developed countries. The incidence in Spain in the decade 1980-1989 was about 5.7%. LBW is generally associated with situations in which uterine malnutrition is produced due to alterations in placental circulation. There are many known risk factors, the most important of which are socio-economic factors, medical risks before or during gestation and maternal lifestyles. However, although interventions exist to prevent many of these factors before and during pregnancy, the incidence of LBW has not decreased.

The use of pesticides in a Polish rural population and its effect on birth weight

INTRODUCTION

The risk of adverse reproductive outcomes related to pesticide exposure has been investigated in few studies; however, the results have not been consistent. The goal of the present study was to evaluate the influence of maternal residual exposure to pesticides on birth weight among women in an agricultural district in Central Poland.

METHOD

Subjects included 104 women who delivered a single, live infant between 1 January 1994 and 31 December 2000. Based on maternal reports, the type of farming (crops, orchards, non-farming jobs), involvement in field work and the trade names of pesticides used within last pregnancy were established. Birth weight for the most recent pregnancy was abstracted from the medical data of the local maternity unit.

RESULTS

Mothers who reported involvement in field work had a similar pregnancy duration but delivered infants with a significantly higher birth weight than mothers not reporting such activities in the first or second trimester of pregnancy (P=0.04). However, after controlling for pregnancy duration and other factors affecting birth weight, we found that maternal exposure to synthetic pyrethroids in the first or second trimester was associated with a small but statistically significant decrease in birth weight (P=0.02).

CONCLUSIONS

We postulate that the observed effect of pyrethroids exposure was related to a slower pace of foetal development corresponding to the small-for-gestational-age (SGA) birth.