Parental occupation and preterm births: a nationwide epidemiological study in Sweden

Prevalence of preterm birth in Scandinavian countries: a systematic review and meta-analysis

OBJECTIVES

As welfare societies, Scandinavian countries share characteristics of equality related to healthcare access, gender, and social services. However, cultural and lifestyle variations create country-specific health differences. This meta-analysis assessed the prevalence of preterm birth (PTB) and its categories in Scandinavian countries.

METHODS

A systematic search in key databases of literature published between 1990 and 2021 identified studies of the prevalence of PTB and its categories. Following the use of the Freeman-Tukey double arcsine transformation, a meta-analysis of weighted data was performed using the random-effects model and meta-prop method.

RESULTS

We identified 109 observational studies that involved 86,420,188 live births. The overall pooled prevalence (PP) of PTB was 5.3% (PP = 5.3%, 95% confidence interval [CI] 5.1%, 5.5%). The highest prevalence was in Norway (PP = 6.2%, 95% CI 5.3%, 7.0%), followed by Sweden (PP = 5.3%, 95% CI 5.1%, 5.4%), Denmark (PP = 5.2%, 95% CI 4.9%, 5.3%), and Iceland (PP = 5.0%, 95% CI 4.4%, 5.7%). Finland had the lowest PTB rate (PP = 4.9%, 95% CI 4.7%, 5.1%).

CONCLUSIONS

The overall PP of PTB was 5.3%, with small variations among countries (4.9%-6.2%). The highest and lowest PPs of PTB were in Norway and Finland, respectively.

Changes in preterm and extremely preterm birth rates in Japan after the introduction of obstetrical practice guidelines in 2008

AIM

Obstetrical guidelines were established in Japan in 2008, and obstetrical diagnoses and treatments were subsequently standardized nationally. We examined changes in the preterm birth rate (PTBR) and extremely preterm birth rate (EPTBR) following the introduction of such guidelines.

METHODS

Information on 50 706 432 live births in Japan between 1979 and 2021, including Japanese reproductive medicine, the childbearing age of pregnant women, and the employment status of reproductive-age women between 2007 and 2020, were obtained from the Japanese government and academic societies. Regression analysis was used to compare chronological changes nationally and those of eight Japanese regions. Regional and national average PTBRs and EPTBRs from 2007 to 2020 were compared by using a repeated measures analysis of variance.

RESULTS

From 1979 to 2007, PTBRs and EPTBRs in Japan increased significantly. However, from 2008, the national PTBR and EPTBR decreased until 2020 (p < 0.001) and 2019 (p = 0.02), respectively. From 2007 to 2020, overall PTBR and EPTBR were 5.68% and 0.255%, respectively. A significant difference in the PTBR and EPTBR existed between the eight Japanese regions. During this period, the number of pregnancies using assisted reproductive technology increased from 19 595 to 60 381, pregnant women became older, the employment rate of those of reproductive age increased, and nonregular employment was 54%, which was 2.5 times higher than for men.

CONCLUSIONS

In Japan, after obstetrical guidelines were enacted in 2008, PTRBs decreased significantly even under the pressure of increasing preterm births. Countermeasures may be necessary for regions showing high PTBRs.

Pregnancy Outcome in Women Exposed to Metal Fume in Welding: A Canadian Cohort Study

OBJECTIVES

Welding is a physically demanding job that entails exposure to metal fume and particles. There is little information on the effect of welding exposures on the outcome of a pregnancy conceived during a period when a woman was employed as a welder.

METHODS

Women welders recruited to the Workers Health in Apprenticeship Trades-Metal and Electrical (WHAT-ME) study were followed-up every 6 months for up to 5 years (January 2011-August 2018), and every pregnancy recorded. At the first 6-month follow-up, a detailed questionnaire was completed for the most recent day in welding, and this information was collected again at each follow-up and also from questionnaires completed during pregnancy. The date of conception was estimated for each pregnancy and the job at that date identified. Exposures to ergonomic factors, work schedule and perceptions of noise, heat and cold were extracted for the job at conception. Exposures to metals (aluminum, chromium, manganese, and nickel) and particles in welding fume were estimated from previously validated exposure algorithms reflecting the welding process, base metal and consumables of the job at the conception date. The effects of exposures were estimated in multilevel multivariable models allowing for confounding.

RESULTS

There were 242 pregnancies conceived by a welder working in her trade, 87 were before the first follow-up, 3 were after first follow-up but detailed information was not collected, 22 of those potentially included in the assessment group were in-trade but not welding leaving 122 pregnancies in 90 welders for analysis. Of these 91 resulted in a live birth and 31 in a fetal loss (27 miscarriages and 4 stillbirths). Mean birth weight for live births was 3365 g and gestation 39.4 weeks. Final models showed that risk of fetal loss increased with manipulating heavy objects [odds ratio (OR) = 5.13, 95% confidence interval (CI) 2.04-12.92], whole-body vibration (OR = 5.86, 95% CI 1.81-18.92), a higher rating for noise exposure intensity (OR = 1.52, 95% CI 1.24-1.85), and decreased with use of local exhaust ventilation (OR = 0.20, 95% CI 0.03-1.18). Gestation decreased with perceived heat intensity (β = -0.15, 95% CI -0.29 to -0.02) and number of previous pregnancies (β = -0.35, 95% CI -0.65 to -0.05). Birth weight was lower in those reporting whole-body vibration (β = -596 g, 95% CI -924 to -267) and increased with the welder's body mass index (β = 36 g, 95% CI 12-61). Estimates of exposure to metals and particles were unrelated to gestation or birth weight. In a bivariate analysis, allowing for the same welder reporting >1 pregnancy, estimated airborne aluminum exposure (and to a lesser degree exposure to nickel and particles) was related to greater risk of fetal loss (OR = 1.52, 95% CI 1.04-2.24) but neither aluminum nor the other estimated elements of welding fume added to the final model.

CONCLUSIONS

In this group of women actively engaged in welding during the time surrounding conception, the outcome of pregnancy was strongly related to work exposures, particularly vibration (reported in grinding tasks), manipulation of heavy objects, and perceived intensity of noise and heat. The study was unable to show an independent effect of exposure to metal fume constituents.

Internal and External Resources and the Adjustment of Parents of Premature Infants

Studies have shown premature birth and infant hospitalization to be associated with increased levels of parental distress. Internal and external psychological resources have been found to mitigate distress among persons coping with stressful medical events. The current study evaluated psychological resources and distress in 87 parents (57 mothers and 30 fathers) to whom an infant was born prematurely and hospitalized in the NICU of a large tertiary medical center. Parents were administered standardized measures of internal (problem-solving skills) and external (total spousal support, adequacy of spousal support) psychological resources and of psychological distress (depression, posttraumatic symptoms, and mood). Findings indicated that higher levels of problem-solving skills and more adequate spousal support, but not total spousal support, were related to lower levels of parental distress. Adequacy of spousal support and parents' problem-solving skills accounted for 18% of the variance in overall mood and 13.8% of the variance in posttraumatic stress symptoms. A significant two-way interaction was found between adequacy of spousal support and problem-solving skills such that individuals with better problem-solving skills reported better overall mood independent of the adequacy of spousal support they receive. However, for individuals with poor problem-solving skills, the adequacy of the spousal support they receive was a significant factor in determining their overall mood. The theoretical and clinical implications of these findings are discussed in terms of the accessibility of these resources to assessment and their potential for change via existing intervention approaches.

Gestational age at birth and risk of intellectual disability without a common genetic cause

Preterm birth is linked to intellectual disability and there is evidence to suggest post-term birth may also incur risk. However, these associations have not yet been investigated in the absence of common genetic causes of intellectual disability, where risk associated with late delivery may be preventable. We therefore aimed to examine risk of intellectual disability without a common genetic cause across the entire range of gestation, using a matched-sibling design to account for unmeasured confounding by shared familial factors. We conducted a population-based retrospective study using data from the Stockholm Youth Cohort (n = 499,621) and examined associations in a nested cohort of matched outcome-discordant siblings (n = 8034). Risk of intellectual disability was greatest among those born extremely early (adjusted OR_{24 weeks} = 14.54 [95% CI 11.46-18.44]), lessening with advancing gestational age toward term (aOR_{32 weeks} = 3.59 [3.22-4.01]; aOR_37weeks = 1.50 [1.38-1.63]); aOR_{38 weeks} = 1.26 [1.16-1.37]; aOR₃₉ weeks = 1.10 [1.04-1.17]) and increasing with advancing gestational age post-term (aOR_{42 weeks} = 1.16 [1.08-1.25]; aOR_{43 weeks} = 1.41 [1.21-1.64]; aOR_{44 weeks} = 1.71 [1.34-2.18]; aOR_{45 weeks} = 2.07 [1.47-2.92]). Associations persisted in a cohort of matched siblings suggesting they were robust against confounding by shared familial traits. Risk of intellectual disability was greatest among children showing evidence of fetal growth restriction, especially when birth occurred before or after term. Birth at non-optimal gestational duration may be linked causally with greater risk of intellectual disability. The mechanisms underlying these associations need to be elucidated as they are relevant to clinical practice concerning elective delivery around term and mitigation of risk in post-term children.

Pathways of job style and preterm low birth weight

Introduction

Preterm and low birth weight tend to occur as a direct result of prenatal risky behaviors, diseases, as well as fetal exposure to harmful social and environmental factors. The present study aimed to investigate the relationship between job style and preterm low birth weight.

Methods

The present case-control study was conducted in the Kamali hospital, Teheran, Iran in 2014. Participants included 156 mothers having a gestational age of less than 37 weeks and infants weighing less than 2500 gm. Additionally, the control group consisted of 433 mothers with a gestational age of over 37 weeks and having infants weighing between 2500–4000 gm. The data were collected using the Mother’s Lifestyle Scale (MLS) during pregnancy based on recognized social determinants of health and those developed by the researchers. The domain of the mother’s job style was assessed using a questionnaire consisting of 18 items on topics such as working conditions, job satisfaction, and perceived employer empathy. Higher overall scores in this instrument indicate the mother’s poorer job style. The data were analyzed using SPSS version 16 and Lisrel version 8.8 through a statistical path analysis.

Results

The model fit indices indicated that there was found to be high favorability, demonstrated that the model fit and that there were rational relationships (CFI=1, RMSEA=0.00), and showed that on the direct path that the mother’s job style had the most adverse effect (B=−0.3) with weight gain during pregnancy showing the most positive effect (B=0.16) on PLBW. The mother’s level of education was found to be the only variable that affected PLBW negatively in both the direct and indirect paths through the mother’s job style and household income (B=−0.17).

Conclusion

According the path analysis model, job style has a direct influence on preterm low birth weight. Thus, special consideration should be placed on aspects surrounding a mother’s job situation in order to prevent any adverse effects.

Psychosocial factors in pregnancy and birthweight: Path analysis

AIM

Birthweight is known to be affected by several factors. In the present study a relationship model of psychological and economic determinants of birthweight was designed and tested.

METHODS

This prospective study involved 400 pregnant women in four districts of Tehran, Iran. The subjects were selected through a multistage sampling method. Seven questionnaires (socioeconomic status; Holmes and Rahe Stress Scale; Perceived Stress Scale; 21-item Depression, Anxiety, and Stress Scale [DASS-21]; perceived social support; pregnancy-related anxiety scale; and domestic violence questionnaire) were used to assess participant psychosocial and economic conditions. In order to collect post-partum information about the mother and the infant, the women were followed up until delivery. Data were analyzed using SPSS-16 and Lisrel-8.8.

RESULTS

Based on the obtained path diagram, the greatest adverse effects on birthweight were exerted directly by DASS-21 score (B = -0.14) and indirectly by stressful life events (B = -0.037). Among variables that affected birthweight in both paths, socioeconomic status and perceived stress had the strongest overall effects on birthweight (B = 0.203 and -0.1024, respectively).

CONCLUSION

According to the path analysis model, psychosocial and economic factors can directly/indirectly affect birthweight.

Environmental and socio-economic determinants of infant mortality in Poland: an ecological study

BACKGROUND

Health status of infants is related to the general state of health of women of child-bearing age; however, women's occupational environment and socio-economic conditions also seem to play an important role. The aim of the present ecological study was to assess the relationship between occupational environment, industrial pollution, socio-economic status and infant mortality in Poland.

METHODS

Data on infant mortality and environmental and socio-economic characteristics for the 66 sub-regions of Poland for the years 2005-2011 were used in the analysis. Factor analysis was used to extract the most important factors explaining total variance among the 23 studied exposures. Generalized Estimating Equations model was used to evaluate the link between infant mortality and the studied extracted factors.

RESULTS

Marked variation for infant mortality and the characteristics of industrialization was observed among the 66 sub-regions of Poland. Four extracted factors: "poor working environment", "urbanization and employment in the service sector", "industrial pollution", "economic wealth" accounted for 77.3% of cumulative variance between the studied exposures. In the multivariate regression analysis, an increase in factor "poor working environment" of 1 SD was related to an increase in infant mortality of 40 (95% CI: 28-53) per 100,000 live births. Additionally, an increase in factor "industrial pollution" of 1 SD was associated with an increase in infant mortality of 16 (95% CI: 2-30) per 100,000 live births. The factors "urbanization and employment in the service sector" and "economic wealth" were not significantly related to infant mortality.

CONCLUSION

The study findings suggested that, at the population level, infant mortality was associated with an industrial environment. Strategies to improve working conditions and reduce industrial pollution might contribute to a reduction in infant mortality in Poland.

Preterm birth and prenatal maternal occupation: the role of Hispanic ethnicity and nativity in a population-based sample in Los Angeles, California

OBJECTIVES

We investigated preterm birth (PTB) in relation to maternal occupational exposure and whether effect measures were modified by Hispanic ethnicity and nativity in a population-based sample with high proportion of Hispanics.

METHODS

We used a case-control study (n = 2543) nested within a cohort of 58,316 births in Los Angeles County, California, in 2003. We categorized prenatal occupations using the US Census Occupation Codes and Classification System and developed a job exposure matrix. Odds ratios for PTB were estimated using logistic regression.

RESULTS

Odds ratios for PTB were increased for all women in health care practitioner and technical occupations, but the 95% confidence intervals included the null value; effects were more pronounced among Hispanics. We estimated elevated odds ratios for foreign-born Hispanic women in building and grounds cleaning and maintenance occupations. Shift work and physically demanding work affected births among US-born but not foreign-born Hispanics.

CONCLUSIONS

Hispanic women are at particular risk for PTB related to adverse prenatal occupational exposure. Nativity may moderate these effects on PTB. Maternal occupational exposures likely contribute to ethnic disparities in PTB.

Growth of Korean preterm infants in a family-centered tradition during early infancy: the influence of health risks, maternal employment, and the sex of infants

AIM

The physical growth of mild preterm infants (<32 weeks of gestation at birth) needs to be explored in terms of bio-sociocultural factors considering the sociocultural aspects of child-care practice.

METHODS

A retrospective cohort study was conducted with 238 Korean mild preterm infants from birth up to 6 months of corrected age regarding four of the biological and sociocultural factors such as health risks (at birth and discharge), maternal employment status, and the infant sex.

RESULTS

There were four noteworthy findings on growth variation in Korean mild preterm infants during early infancy: (i) the secular trend of intrauterine growth; (ii) the cumulative adverse effects of four risk factors; (iii) the possible burden of maternal employment if insufficient support; and (iv) the possibility of the cultural favoritism to male infants regardless of the modern industrialized society.

CONCLUSION

The study suggests that, in a modern society, while mild preterm infants could sustain typical fetal growth, the early postnatal growth may vary based on health risks and sociocultural circumstances related to child-bearing and -rearing practices surrounding them.

Multiple pregnancy, short cervix, part-time worker, steroid use, low educational level and male fetus are risk factors for preterm birth in Japan: a multicenter, prospective study

AIM

To examine the relationship between preterm birth and socioeconomic factors, past history, cervical length, cervical interleukin-8, bacterial vaginosis, underlying diseases, use of medication, employment status, sex of the fetus and multiple pregnancy.

METHODS

In a multicenter, prospective, observational study, 1810 Japanese women registering their future delivery were enrolled at 8⁺⁰ to 12⁺⁶ weeks of gestation. Data on cervical length and delivery were obtained from 1365 pregnant women. Multivariate logistic regression analysis was performed.

RESULTS

Short cervical length, steroid use, multiple pregnancy and male fetus were risk factors for preterm birth before 34 weeks of gestation. Multiple pregnancy, low educational level, short cervical length and part-timer were risk factors for preterm birth before 37 weeks of gestation.

CONCLUSION

Multiple pregnancy and cervical shortening at 20-24 weeks of gestation was a stronger risk factor for preterm birth. Any pregnant woman being part-time employee or low educational level, having a male fetus and requiring steroid treatment should be watched for the development of preterm birth.

Preterm delivery and psycho-social determinants of health based on World Health Organization model in Iran: a narrative review

Background:

Preterm delivery is still the primary cause of mortality and morbidity in infants, which shows a problematic condition in the care of pregnant women all over the world. This review study describes prevalence and psycho - socio-demographic as well as obstetrical risk factors related to live preterm delivery (PTD) in the recent decade in Iran.

Methods:

A narrative review was performed in Persian and international databases including PubMed, SID, Google Scholar, Iran Medex, Magiran and Irandoc from 2001 to 2010 with following keywords: preterm delivery and pregnancy outcomes with (prevalence, socioeconomic condition, structural determinant, Intermediary determinants, Psychosocial factor, Behavioral factor and Maternal circumstance, Health system) All of article was reviewed then categorized based on WHO model.

Results:

Totally 52 article were reviewed and 35 articles were selected, of which 26 were cross-sectional or longitudinal, 9 were analytical (cohort or case-control). The prevalence rates of preterm delivery in different cities of Iran were reported between 5.6% in Quom to 39.4% in Kerman. The most common social factors in structural determinant were educational level of mother, and in intermediary determinants were Psychosocial factor (maternal anxiety and stress during pregnancy), Behavioral factor and Maternal circumstance (violation and trauma) and in Health system, lack of prenatal care.

Conclusion:

The prevalence rate of preterm delivery is a matter of concern. Since many psycho-social factors may affect on the condition and its high rate in poor communities might reveals a causal relationship among biological and psychosocial factors, performing etiological investigations is recommended.

Occupational exposure to chemicals and fetal growth: the Generation R Study

BACKGROUND

Developmental diseases, such as birth defects, growth restriction and preterm delivery, account for >25% of infant mortality and morbidity. Several studies have shown that exposure to chemicals during pregnancy is associated with adverse birth outcomes. The aim of this study was to identify whether occupational exposure to various chemicals might adversely influence intrauterine growth patterns and placental weight.

METHODS

Associations between maternal occupational exposure to various chemicals and fetal growth were studied in 4680 pregnant women participating in a population-based prospective cohort study from early pregnancy onwards in the Netherlands (2002–2006), the Generation R Study. Mothers who filled out a questionnaire during mid-pregnancy (response: 77% of enrolment) were included if they conducted paid employment during pregnancy and had a spontaneously conceived singleton live born pregnancy (n = 4680). A job exposure matrix was used, linking job titles to expert judgement on exposure to chemicals in the workplace. Fetal growth characteristics were repeatedly measured by ultrasound and were used in combination with measurements at birth. Placental weight was obtained from medical records and hospital registries. Linear regression models for repeated measurements were used to study the associations between maternal occupational exposure to chemicals and intrauterine growth.

RESULTS

We observed that maternal occupational exposure to polycyclic aromatic hydrocarbons, phthalates, alkylphenolic compounds and pesticides adversely influenced several domains of fetal growth (fetal weight, fetal head circumference and fetal length). We found a significant association between pesticide and phthalate exposure with a decreased placental weight.

CONCLUSIONS

Our results suggest that maternal occupational exposure to several chemicals is associated with impaired fetal growth during pregnancy and a decreased placental weight. Further studies are needed to confirm these findings and to assess post-natal consequences.