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Ergonomic demands and fetal loss in women in welding and electrical trades: A Canadian cohort study

Abstract Objectives To determine the relationship between ergonomic demands of the job at conception and fetal loss (miscarriage or stillbirth). Methods Women with a welding or electrical trade apprenticeship were identified across Canada for the Women's Health in Apprenticeship Trades–Metal and Electrical study. They completed a reproductive and employment history at recruitment and every 6 months for up to 5 years to provide details on pregnancies and work demands. Job at conception was identified and fetal loss examined in relation to ergonomic exposures/demands, allowing for potential confounders. Results A total of 885 women were recruited; 447 in welding and 438 in electrical trades. Of these, 574 reported at least one pregnancy. Analysis of 756 pregnancies since the woman started in her trade suggested no increased risk of fetal loss in those choosing welding rather than electrical work. Among 506 pregnancies conceived during a period working in a trade, 148 (29.2%) ended in fetal loss: 31.2% (73/234) in welding, and 27.6% (75/272) in electrical work. Detailed exposure information was available for 59% (299/506) of these pregnancies. In welders, the risk of fetal loss was increased with whole‐body vibration (prevalence ratio [PR] = 2.14; 95% confidence interval [CI] 1.39–3.31) and hand‐arm vibration for > 1 hour/day (PR = 2.15; 95% CI 1.33–3.49). In electrical workers risk increased with more than 8 days working without a rest day (PR = 2.29; 95% CI 1.25–4.17). Local exhaust ventilation reduced risk in welders. Conclusions There was no significant increase in fetal loss in welding trades compared to electrical work. Vibration, largely from grinding, and extended work rotations appear to be potentially modifiable factors of some importance.


| INTRODUCTION
As women move into work previously carried out mainly by men, there may be justified concern that exposure guidelines based on the experience of male workers may be ill-suited to protect either woman with the same exposures or the fetus if a woman becomes pregnant. Welding is one trade that has raised concerns about pregnancy. Since women have, until recently, entered welding in small numbers, information on pregnancy outcomes has been based on women identified as metal workers or welders in community-based studies. [1][2][3][4][5] Data reported from these studies are consistent with increased risk of spontaneous abortion, 3 low birth weight, 1,2,4,5 and prematurity. 5 Multiple hazards to the fetus may be in play, including substantial ergonomic demands, from the welding itself, the manipulation of heavy components, and the body postures needed to reach parts to be welded. Recent systematic reviews and meta-analyses have supported the role of heavy physical work in poor pregnancy outcomes. 6,7 In Western Canada, much of the demand for welders and other tradespeople has been in the oil fields, with exposure to harsh conditions, including long working schedules implicated in adverse pregnancy outcomes. 8 In response to a request from the Canadian Standards Association, a protocol was developed to recruit women welders and, as a comparison group, women in the electrical trades. This study, of Women's Health in Apprenticeship Trades-Metal and Electrical (WHAT-ME), was designed to investigate whether work as a welder was associated with adverse pregnancy outcomes and to help identify any exposures responsible. The present paper addresses one outcome, fetal loss (miscarriage or stillbirth), poorly addressed in record linkage or point of delivery studies 2 | METHODS Preparations to set up cohorts of women in the welding and electrical trades began in 2010, following preliminary work to determine whether such a study would be acceptable to women in the trades and to develop self-report questionnaires that accurately reflected welding tasks. 9 Women entering apprenticeships from 2005 to 2014 in welding (welding, boiler-making, steam fitting, and pipefitting) and electrical (commercial, industrial, or residential) trades were identified by apprenticeship boards (or equivalent) across Canada. 10 The board sent a letter to each apprentice or tradesperson identified, inviting them to complete a consent form and forward it to the research team. Baseline information was collected by telephone or online, in English or French, when the consent form was received. Women were subsequently contacted at 6-month intervals for up to 5 years.
Participants were not paid for taking part in the study.
The baseline questionnaire collected demographic and health information, a job history, use of tobacco and alcohol, and details of all pregnancies and births. At each 6-month follow-up, the use of tobacco and alcohol was brought up to date, all jobs since the last contact were recorded and questionnaires were completed about tasks and activities on the last day on which they carried out their trade.
Women were asked to notify us as soon as they became pregnant (with a positive pregnancy test), by phoning a toll-free line, by email, or by sending back a "pregnancy card," a distinctive prefranked postcard distributed at recruitment and at intervals during the study. Every follow-up questionnaire also asked about pregnancies since the last contact, and a "wrap-up" questionnaire sent at the end of the study, included a question specifically on miscarriages, potentially underreported at the periodic follow-up contacts.
Pregnancy outcomes reported by the participant were: fetal loss (spontaneous abortion or stillbirth) at any gestation, and, for live births, gestation in weeks and birth weight. For those living in Alberta, linkage was made (with consent) to the administrative health database from which dates of physician-consulted miscarriages were retrieved. Stillbirths were found also from the provincial perinatal register. When a woman reported a pregnancy, she was asked to complete two questionnaires (usually in the first and third trimester) and a further one post-pregnancy. The conception date was estimated for each pregnancy, from the date of the last menstrual period where reported on a pregnancy questionnaire, or from reported gestation. Where no gestation data were available for a miscarriage, this was assumed to be at eight weeks (the median length for those with such data). The estimated date of conception was linked to the employment record to determine occupation and exposures close to the time of conception.
Exposures of interest were, for all women, whether or not they were in paid employment at the date of conception and, if they were, whether this was in their trade (welding or electrical work) or elsewhere. For those working in trade at conception, we considered ergonomic demands (hours manipulating heavy objects, standing, crouching, working above shoulder height, driving, working in a noisy, hot or cold job environment, work with tools or equipment causing hand/arm or whole-body vibration, work schedules (hours of work, maximum days worked without a rest day, and number of consecutive nights worked after midnight) and factors influencing respiratory exposure (percentage of time using a respirator, working with general mechanical ventilation, local exhaust ventilation (LEV), outdoors, or in a confined space). Six participants had missing information on the perceived intensity of heat, cold, and noise: for those with missing values ratings were estimated from the median intensity of those with the same hours of exposure.
An example of the follow-up questionnaire used for welders is included as Appendix A and information on the construction of exposure variables in Appendix B.

| Statistical methods
Differences between those in the welding and electrical trades in baseline characteristics and pregnancy outcomes were evaluated by χ 2 tests. Mean differences in exposures were examined by analysis of variance. The effects of exposures at conception were estimated in multilevel Poisson models with robust standard errors, allowing for more than one conception for each participant (clustering) and adjusting for confounders. Where the Poisson model failed to converge an estimate was made (and noted) using a logistic model. Exposures were considered either as continuous factors (hours, percentage of time, rating of noise, heat, and cold) or as categorical variables. For this they were grouped first into approximate tertiles, using the closest whole unit as the breakpoint, and the lowest tertile of exposure used as the comparison group. The tertiles were collapsed to binary factors for later analyses. Where less than a third had been exposed, the binary (any/none) grouping was used throughout.  Table 1. Women in welding were younger at recruitment than those in the electrical trades, more likely to smoke cigarettes and, if they drank alcohol, to report rather more drinks per week.
Pregnancies since started in a trade that ended in miscarriage or stillbirth (fetal loss) are shown in Table 2. In this unadjusted analysis, there was a little evident difference in outcome for those recruited from the welding and electrical trades. Fetal loss was not more common among those working in their trade, but all eight stillbirths among these 756 pregnancies were conceived while the woman was in her trade, five in welders, three in electricians. The relation of potential confounders to outcome is shown in Table 3 for welders and those in electrical work in their trade at conception. Age, smoking cigarettes, the number of previous pregnancies, and a previous fetal loss were retained as potential confounders for the analysis of in-trade pregnancies. In a multivariable analysis of Table 2, allowing for clustering within women, work status, and potentially confounding factors from Table 3, no overall difference in risk of fetal loss was found between women entering the welding and electrical trades, among the 756 women who conceived after entering the trade (odds ratio [OR] for welder = 1.09 95% confidence interval [CI] 0.88-1.35).
The means of the 18 dimensions of work for in-trade pregnancies in welders and electrical workers are shown in Table 4. Those in welding spent more time than those in electrical work manipulating heavy objects, standing, and exposed to whole body and hand/arm vibration. They were also more likely to report wearing a respirator and working with general mechanical ventilation and to work in noisy and hot jobs. Those in the electrical trades spent more time crouching or kneeling down. The relation of fetal loss to each exposure is shown as a crosstabulation in Table 5 which includes only factors that showed some relation (p < 0.10), in at least one trade group, to fetal loss. After adjustment for clustering, only long hours of work (>10 h), work in confined space or in a colder job and a job requiring long rotations without a rest day (maximum > 8 days) were associated with an increased risk of fetal loss for those in the electrical trades (Table 6). Working in an environment with consistent general mechanical ventilation decreased risk. Among welders, the use of tools

| DISCUSSION
The study reported here was designed to establish whether pregnancy outcomes were worse than expected in women who conceived while working in the welding trades and to determine factors that might be responsible. Overall, the results for fetal loss did not suggest the worst outcome in welding than in the comparison group of women entering the electrical trades.
The strength of the study lies in the repeated measures prospective design, in which information about work demands around the time of conception was collected before the outcome of the pregnancy was known. Where this did not happen as planned, this was also a weakness: when a woman sustained an early miscarriage, exposure estimates were taken from whichever questionnaires described the job at conception. If this was collected post-event, the possibility of reporting bias cannot be excluded. The design did, however, give confidence that very few pregnancies were missed completely and the quality of the information on numbers, dates, and outcomes of pregnancies is likely to be higher than in a retrospective design. Moreover, it allowed analysis of miscarriages using nearcontemporary exposure data. Although the level of collaboration was high in those recruited, those who took part may have been unrepresentative of all women in these trades. Estimates suggest a take-up rate of at most 15% of tradeswomen 10   In the present study, vibration, which arose largely from the use of grinding tools, was associated with fetal loss in welders.
Vibration was included as a risk factor by McDonald and colleagues 3 in their study of fetal loss and found to relate particularly to an increase in late abortions and stillbirths. Whole-body vibration, assigned by a job exposure matrix, has recently been reported, from Sweden, to relate to preterm birth but not low birthweight, 11 with similar findings, using self-report of vibration exposure, in Nigeria 12 and Canada. 13 The observed protective effects of consistent mechanical ventilation for those in the electrical trades and of local exhaust ventilation in welders, flags up the need for wider implementation, but we cannot rule out the possibility that these may be markers for a particular type of task or employer (e.g., one willing to invest in the safety of the worker) rather than necessarily a direct effect of a reduced concentration of airborne contaminants toxic to the fetus.

CONFLICTS OF INTEREST
The authors declare no conflicts of interest.

DISCLOSURE BY AJIM EDITOR OF RECORD
John Meyer declares that he has no conflict of interest in the review and publication decision regarding this article.

ETHICS APPROVAL AND INFORMED CONSENT
The project was reviewed by the Health Ethics Review Board of the University of Alberta (Pro00017851). All participants gave written informed consent.

AUTHOR CONTRIBUTIONS
The project was conceived by Nicola Cherry and Jeremy Beach and data collected under their guidance. The analysis was carried out by Jean-Michel Galarneau and Nicola Cherry. Nicola Cherry drafted the final report which was critically reviewed and amended by all authors.
All have approved the final version and agree to be accountable for all aspects of the work.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the corresponding author upon reasonable request.   h. Ratings on a scale from 1 to 10 of the noisiest, hottest, coldest job done on the most recent day at work CHERRY ET AL.