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Obstetrics & Gynecology 2001;97:361-365
© 2001 by The American College of Obstetricians and Gynecologists
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ORIGINAL RESEARCH

Blood Pressure in Late Pregnancy and Work Outside the Home

SUSAN P. WALKER, FRANZCOG, MICHAEL PERMEZEL, MD, FRANZCOG, SHAUN P. BRENNECKE, DPhil, (Oxon), FRANZCOG, ANTONY M. UGONI, MS and JOHN R. HIGGINS, MD, FRANZCOG

From the University Department of Obstetrics and Gynaecology, Mercy Hospital for Women, and Department of Perinatal Medicine, Royal Womens’ Hospital, and Department of General Practice and Public Health, University of Melbourne, Melbourne, Australia.

Address reprint requests to: Susan P. Walker, FRANZCOG, University Department of Obstetrics and Gynecology, Mercy Hospital for Women, Clarendon Street, East Melbourne, 3002, Victoria, Australia, E-mail: s.walker{at}pgrad.unimelb.edu.au


   Abstract
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Abstract
Materials and Methods
 Results
 Discussion
 References
 
Objective: To assess maternal blood pressure (BP) responses to working outside the home in late pregnancy, using 24-hour ambulatory BP monitoring.

Methods: Our paired observational study involved 24-hour ambulatory BP monitoring of 100 normotensive women (51 primiparas, 49 multiparas) on work and nonwork days. Mean BP differences were calculated for working, postworking, sleeping, and 24-hour periods on both days. Main outcome measures were BP differences between work and nonwork days and subsequent pregnancy hypertension. Comparisons in BP between work and nonwork days were done with Student paired t test. Comparisons between study subgroups were done with unpaired t test. Potential predictors of change in BP were examined using multiple linear regression.

Results: During job time, BP was significantly higher on work days than on nonwork days. The mean increase in BP associated with work was 2.6 mmHg (systolic BP, P < .001), 2.8 mmHg (diastolic BP, P < .001), and 2.9 mmHg (mean arterial BP, P < .001). Those observations were independent of parity. More than 10% of our subjects had increased mean arterial BP of 10 mmHg or more during job time on work days compared with nonwork days. Higher absolute BP levels (regression coefficient 0.21, P = .04) and greater perceived job stress (regression coefficient 1.34, P = .04) correlated positively with BP increases at work. Twelve women developed hypertension. Those women had a larger increase on work days in mean systolic (6.6 mmHg compared with 2.1 mmHg, P = .013), mean diastolic (6.4 mmHg compared with 2.3 mmHg, P = .014), and mean arterial (7.4 mmHg compared with 2.3 mmHg, P = .002) BP compared with normotensive women. The magnitude of BP responses to work was a significant predictor of pregnancy hypertension, independent of absolute BP level.

Conclusion: Blood pressure increased in women when they worked outside the home. The effect of maternal work is important when treating pregnancy hypertension. Ambulatory BP monitoring makes assessment of maternal BP responses to work a practical clinical option.

Increasing numbers of women continue to work outside the home during late pregnancy.1 The impact of work on pregnancy outcomes is controversial. Most research has focused on the effect of maternal work on preterm delivery and fetal growth restriction (FGR). Recent literature reviews have confirmed the controversial effect of work on those outcomes.2,3 Those conflicting results might be explained partly by not accounting for confounding effects of differing domestic workloads and the healthy worker effect, in which women who work are more likely to be educated, of higher socioeconomic status, smoke less, and present for antenatal care earlier in pregnancy.

Associations between work and an increased incidence of pregnancy hypertension also have been described.4 Those associations appear stronger when work is physically strenuous5 or perceived as stressful.6,7 Studies in nonpregnant populations, using ambulatory blood pressure (BP) monitoring, found that work is associated with significant increases in BP.8–10 Ambulatory BP monitoring enables multiple BP readings to be taken in a nonclinic environment over 24 hours and overcomes many problems with clinic BP measurement, including measurement error, observer error and bias, and "white coat" responses.11 Therefore, ambulatory BP monitoring is the ideal instrument to examine BP responses to work. Several devices have been validated specifically in pregnancy.12,13 Working women have higher daytime ambulatory BP in midpregnancy compared with nonworking women (J. Higgins, personal communication). Blood pressure responses to work in the third trimester might be greater, when the absolute BP level is highest, vascular reactivity is highest, and the physical burden of pregnancy is greatest.

We compared maternal ambulatory BP in the same individuals, recorded on work days and nonwork days in late pregnancy. We also compared maternal BP at work and at home in women without children and in women with higher domestic workloads associated with caring for young children.


   Materials and Methods
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Abstract
 Materials and Methods
Results
 Discussion
 References
 
One hundred women were recruited from public antenatal clinics and obstetricians’ practices. This was a convenience sample, with women recruited by information posters and leaflets. All women were at least 30 weeks’ gestation, normotensive (BP under 140/90 mmHg), with singleton pregnancies, and were working outside the home. Shift and part-time workers were excluded. Basic demographic details, including age, gestation at the time of monitoring, parity, and weight were recorded. The occupational characteristics included number of hours worked per day, percentage of work time spent sitting (versus standing and walking), subjective perception of job stress (on a Likert scale of 0–5), and access to regular work breaks. Information on domestic workloads included number of children at home, estimated number of housework hours per day, hired domestic help, and whether moving or renovating. Women were also asked to estimate differences in their caffeine and tobacco intakes between work and nonwork days.

Throughout the study we used the Spacelabs 90207 ambulatory BP monitor (Spacelabs Inc., Redmond, WA), which has been specifically validated for use in pregnancy.12 Recordings were made every 30 minutes over both 24-hour periods, and women were masked to their BP readings. Women kept a diary, which allowed us to individualize job, postjob, and sleeping time on monitoring days. To avoid effects of habituation to wearing the monitor, half the women did their work day monitoring first and the other half did their non-work day first. This nonrandom order was determined by the day on which women did their first monitoring.

At completion of the study, data on maternal hypertensive status during the current pregnancy were collected from medical records. We used the definitions of the International Society for the Study of Hypertension in Pregnancy for gestational hypertension (two BP readings at least 140/90 mmHg or one isolated reading at least 160/100 mmHg) and preeclampsia (hypertension plus at least 300 mg proteinuria per 24 hours or at least + + on two separate occasions).14 When a diagnosis of gestational hypertension or preeclampsia was recorded, it was confirmed independently by two investigators. Written informed consent was obtained from all subjects, and we had the approval of the participating hospitals’ research and ethics committees.

For analysis, each patient’s two 24-hour ambulatory BP profiles were edited into four separate periods (job, postjob, sleep, and 24-hour) using patient diaries, which ensured that identical periods on the work and non-work days were compared. Mean systolic, diastolic, mean arterial BP and mean heart rate were calculated for each period. Comparisons between work and non-work days were done with Student paired t test. Comparisons in BP between study subgroups were done with unpaired t test. The effects of demographic, occupational, and domestic variables on BP differences were analyzed using multiple linear regression. Although not the primary hypothesis of the study, because of its clinical relevance, the relationship between BP changes associated with work and subsequent pregnancy hypertension was examined using logistic regression. Based on a sample of 100, and assuming the standard deviation (SD) of the change in BP between the 2 days to be 5 mmHg, with a two-sided significance set at .05, this study had 98% power to detect a difference in work day and nonwork day BP of 2 mmHg. Based on between-group variability of 7 mmHg, this study had 95% power to detect a difference of 5 mmHg between primigravidas and multigravidas. All analyses were done with the statistical software package SPSS for Windows 95 7.0 (SPSS Inc., Chicago, IL).


   Results
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Abstract
 Materials and Methods
 Results
Discussion
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The clinical and delivery characteristics of subjects are summarized in Table 1Go. The mean ± SD number of days between monitoring was 2.7 ± 2 days. Mean systolic, diastolic, mean arterial BP and mean heart rate were higher for job periods and 24-hour periods when work and nonwork days were compared. There were no significant differences between the 2 days of monitoring for postjob or sleep times (Table 2Go). Diastolic BP, mean arterial BP, and heart rate were significantly higher during job time compared with postjob time, on working days (Table 3Go). Those observations were not altered significantly by parity or order in which the days of monitoring were done.


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  		Table 1. Clinical and Delivery Characteristics
 

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  		Table 2. Mean Blood Pressures on Work and Nonwork Days
 

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  		Table 3. Mean Blood Pressure Differences Between Job and Postjob Periods
 
Although the mean difference between the 2 days for the group was small, many responses were substantial. More than 10% of women had differences in mean arterial BP between the 2 days of 10 mmHg or more during the job time. Given that this level of response has greater clinical relevance, a regression model was developed to identify factors that influenced BP responses to work. The BP difference during job time between work and nonwork days was the dependent variable. The woman’s average mean arterial BP for 48 hours of monitoring and all the demographic, occupational, and domestic variables were explored as potential predictors. Factors associated positively with a larger BP difference between the 2 days were higher absolute BP levels (regression coefficient 0.21, P = .04), greater perceived job stress (regression coefficient 1.34, P = .04), and hired domestic help (regression coefficient 4.25, P = .02). Renovating the house was negatively associated with higher BP at work (regression coefficient -2.91, P = .05). No other variables associated significantly with changes in BP at work.

Twelve women were subsequently classified as having either gestational hypertension (n = 9) or preeclampsia (n = 3). In those women, the increase in systolic, diastolic, and mean arterial BP associated with work was significantly greater than normotensive women (Table 4Go). To confirm that this finding was not caused by higher levels of absolute BP in those women, a logistic regression model was created in which hypertensive outcome was the dependent variable. This analysis confirmed that there remained a significant independent association between change in mean arterial BP at work and subsequent development of pregnancy induced hypertension even after adjusting for absolute mean BP levels (odds ratio 1.24 [OR] 95% confidence interval [CI] 1.07, 1.43; P = .004).


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  		Table 4. Mean Blood Pressure Differences in Job Time Between Work and Nonwork Days: Hypertensive Outcome
 

   Discussion
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Abstract
 Materials and Methods
 Results
 Discussion
References
 
We confirmed a significant increase in BP associated with work outside the home. This increase is at the lower range of that reported in the literature for non-pregnant populations. Enstrom and Pennert9 reported a mean increase of 3 mmHg for systolic and diastolic BP in normotensive men on work days using 24-hour ambulatory monitoring. Pieper et al10 reported a 6 mmHg increase in diastolic BP on work days. Turjanmaa et al8 used intra-arterial monitoring to document changes associated with work; they found a 10 mmHg/5 mmHg (systolic BP/diastolic BP) decrease in BP in the postwork time. Arco-Galan et al15 compared 24-hour BP profiles in doctors during on-call compared with at home days. They found that 40% and 23% of doctors, respectively, had increases of more than 10 mmHg in systolic and diastolic BP.15 In contrast, we found a mean increase in pregnant women of only 2.6 mmHg/2.8 mmHg (systolic/diastolic BP) during job time on working days. However, 10% of pregnant women had increases in mean arterial BP greater than 10 mmHg. Women with higher absolute BP also were more likely to have significant pressor responses to work.

Two studies addressed the effects of differing domestic workloads on ambulatory BP in nonpregnant women. King et al16 found that systolic BP was higher at home than at work in women caring for an ill or frail relative at home. James et al17 did 24-hour ambulatory BP monitoring on 50 women of mixed parity on a work day and found that having more children was strongly associated with higher diastolic BP at home. Although we did not confirm that finding in pregnant women, we found that having hired domestic help was positively associated with higher BP at work. That finding could be interpreted that women with lighter domestic workloads have a greater decrease in BP when they return home. James et al17 also reported that the most powerful behavioral predictor of systolic BP in women at work was perceived job stress. In our study, perceived job stress, reported on a scale of 0–5, associated positively with increased work and nonwork BP differences.

In our study, women who developed pregnancy hypertension were then analyzed separately. We observed significant differences in the magnitude of BP increases between work and nonwork days in women who developed pregnancy hypertension. Logistic regression analysis found that this change in BP was a significant predictor of subsequent pregnancy hypertension. That association was independent of absolute BP level and is consistent with the observation that women who eventually developed pregnancy hypertension had exaggerated pressor sensitivity.18,19 Stratified analysis of women with gestational hypertension and preeclampsia would be ideal, but our small sample precluded such analysis.

Several epidemiologic studies described an association between work and pregnancy hypertension. Eskenazi et al4 reported an OR of 2.1 (95% CI 1.1, 4.4) for preeclampsia among working women compared with unemployed women. Klebanoff et al20 reported that 8.8% of pregnant resident physicians with long work hours developed preeclampsia, compared with 3.5% of male residents’ pregnant spouses. Wergeland and Strand5 reported increased prevalence of preeclampsia in women with heavy physical workloads. Landsbergis and Hatch6 prospectively collected job strain data on 717 women and found that stressful job characteristics were associated with pregnancy-induced hypertension. Klonoff-Cohen et al7 retrospectively assigned job strain scores to 110 preeclamptic women and 115 controls and found that employed women were at higher risk of developing preeclampsia than unemployed women (OR 2.3; 95% CI 1.2, 4.6). There was a trend toward women in high-strain jobs being at increased risk compared with other working women (OR 2.1; 95% CI 0.7, 6.2). The mechanisms underpinning that association are not understood, but higher sympathetic nervous activity recently has been reported in preeclampsia.21 This study lends support to the concept of sympathetic overactivity associated with work preceding preeclampsia in some women.

The limitations of this study need to be appreciated. The commitment required of the women involved in the study means some degree of selection and participation bias is inevitable and that healthy workers might be overrepresented. Manual workers were underrepresented in this cohort, as were women of non-English–speaking background. Those factors might explain why our primigravid population was older than the hospital average (28 years) because older women are more likely to have established careers that enable them to work later in pregnancy. Our study participants might not have displayed the full range of BP responses associated with work. More importantly, the number of women in this low-risk population who developed pregnancy-induced hypertension is predictably low. Thus, whereas this study found that mean BP responses to work showed a significant statistical association with the subsequent pregnancy hypertension, further studies are needed to confirm these findings prospectively.


   Footnotes
 
PII S0029-7844(00)01166-2

Received July 5, 2000. Received in revised form October 10, 2000. Accepted October 26, 2000.


   References
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Abstract
 Materials and Methods
 Results
 Discussion
 References
 
1. Shehan CL. Sociodemographic perspectives on pregnant women at work. Semin Perinatol 1996;20:3–10.[Medline]

2. Walker SP, Higgins JR, Michael MJ, Brennecke SP. Maternal work and pregnancy. Aust N Z J Obs Gyn 1999;39:144–51.

3. Gabbe SG, Turner LP. Reproductive hazards of the American lifestyle: Work during pregnancy. Am J Obstet Gynecol 1997;176: 826–32.[Medline]

4. Eskenazi B, Fenster L, Sidney S. A multivariate analysis of risk factors for preeclampsia. JAMA 1991;266:237–41.[Abstract]

5. Wergeland E, Strand K. Working conditions and prevalence of pre-eclampsia, Norway 1989. Int J Gynecol Obstet 1997;58:189–96.[Medline]

6. Landsbergis PA, Hatch MC. Psychosocial work stress and pregnancy induced hypertension. Epidemiology 1996;7:346–51.[Medline]

7. Klonoff-Cohen HS, Cross JL, Pieper CF. Job stress and preeclampsia. Epidemiology 1996;7:245–9.[Medline]

8. Turjanmaa V, Tuomisto M, Fredrikson M, Kalli S, Uusitalo A. Blood pressure and heart rate variability and reactivity as related to daily activities in normotensive men measured with 24-h intra-arterial recording. J Hypertens 1991;9:665–73.[Medline]

9. Enstrom I, Pennert K. Does it matter whether ambulatory blood pressure is recorded during a work day or a non-work day? J Hypertens 1996;14:565–9.[Medline]

10. Pieper C, Warren K, Pickering TG. A comparison of ambulatory blood pressure and heart rate at home and work on work and non-work days. J Hypertens 1993;11:177–83.[Medline]

11. Pickering TG. Ambulatory monitoring and blood pressure variability. London: Science Press, 1991.

12. Shennan AH, Kissane J, deSwiet M. Validation of the SpaceLabs 90207 ambulatory blood pressure monitor for use in pregnancy. Br J Obstet Gynaecol 1993;100:904–8.[Medline]

13. Halligan A, O’Brien E, O’Malley K, Mee F, Atkins N, Conroy R, et al. Twenty-four ambulatory blood pressure measurement in a primigravid population. J Hypertens 1993;11:869–73.[Medline]

14. Davey DA, MacGillivray I. The classification and definition of the hypertensive disorders of pregnancy. Am J Obstet Gynecol 1988; 158:892–8.[Medline]

15. Arco-Galan C, Suarez-Fernandez C, Gabriel-Sanchez R. What happens to blood pressure when on-call? Am J Hypertens 1994;7: 396–401.[Medline]

16. King AC, Oka RK, Young DR. Ambulatory blood pressure and heart rate responses to the stress of work and caregiving in older women. J Gerontol 1994;49:M239–45.[Medline]

17. James GD, Cates EM, Pickering TG, Laragh JH. Parity and perceived job stress elevate blood pressure in young normotensive women. Am J Hypertens 1989;2:637–9.[Medline]

18. Gant WF, Daley GL, Chand S, Whalley PJ, MacDonald PC. A study of angiotensin II pressor response throughout primigravid pregnancy. J Clin Invest 1973;52:2682–9.

19. Dekker GA, Makovitz JW, Wallenburg HCS. Prediction of pregnancy-induced hypertensive disorders by angiotensin II sensitivity and supine pressor test. Br J Obstet Gynaecol 1990;97:817–21.[Medline]

20. Klebanoff MA, Shiono PH, Rhoads GC. Outcomes of pregnancy in a national sample of resident physicians. N Engl J Med 1990;323: 1040–5.[Abstract]

21. Schobel HP, Fischer T, Heuszer K, Geiger H, Schneider RE. Pre-eclampsia—a state of sympathetic overactivity. N Engl J Med 1996;335:1480–5.[Abstract/Free Full Text]




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