ObjectiveTo assess maternal blood pressure (BP) responses to working outside the home in late pregnancy, using 24-hour ambulatory BP monitoring.MethodsOur 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 pairedttest. Comparisons between study subgroups were done with unpairedttest. Potential predictors of change in BP were examined using multiple linear regression.ResultsDuring 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.ConclusionBlood 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.