Table 5

 Occupational activity and the risks of pre-eclampsia and pregnancy-induced hypertension

First author (year)OutcomeNumbers in analysisRR (95% CI)ExposureHigher potential forIncomplete reporting
h/wk, hours per week; kg/d, kilograms per day; PE, pre-eclampsia.
RR is used generically to encompass a variety of published effect measures (odds ratios, incidence density ratios, hazard ratios etc).
Weekly working hours
    Cohort studies
        Landsbergis PA (1996)22PIH5751.1 (0.2 to 5.7)41–49 vs <35 h/wkTrimester 1NoNoNo
    Case–control studies
        Marcoux S (1999)28PIH2670.85 (0.48 to 1.54)⩾35 vs ⩽21 h/wkFirst 20 weeksNoNoNo
Shift work
    Cross-sectional studies
        Nurminen T (1989)34PIH8900.9 (0.4 to 1.9)2 or 3 shift work vs noneMost of pregnancyNoYesNo
        Wergeland E (1997)53PE32811.3 (0.8 to 1.9)Shift work (yes vs no)Trimester 1NoNoNo
    Cross-sectional studies
        Irwin DE (1994)19PIH24131.1 (0.8 to 1.6)⩾13.6 vs ⩽4.5 kg/dNot statedNoYesNo
        Irwin DE (1994)19PE24200.68 (0.47 to 0.98)⩾13.6 vs ⩽4.5 kg/dNot statedNoYesNo
        Wergeland E (1997)53PE32841.7 (1.2 to 2.5)Lifting heavy loads (10–20 kg; yes vs no)Trimester 1YesNoNo
    Cohort studies
        Saftlas AF (2004)41PIH10091.26 (0.83 to 1.91)Sitting <34% vs ⩾67% of the timeTrimester 1NoNoNo
        Saftlas AF (2004)41PE10090.72 (0.32 to 1.59)Sitting <34% vs ⩾67% of the timeTrimester 1NoNoNo
    Cross-sectional studies
        Irwin DE (1994)19PIH28821.0 (0.71 to 1.4)⩾2/3 vs ⩽1/3 of timeNot statedNoYesNo
        Nurminen T (1989)35PIH6871.1 (0.6 to 2.0)Standing work vs sedentaryTrimester 3YesYesNo
        Irwin DE (1994)19PE28790.82 (0.57 to 1.2)⩾2/3 vs ⩽1/3 of timeNot statedNoYesNo
        Wergeland E (1997)53PE32940.7 (0.5 to 1.0)Standing/walking (yes vs no)Trimester 1YesNoNo
Physical activity
    Cohort studies
        Landsbergis PA (1996)22PIH5750.7 (0.2 to 2.5)Physical activity score (>200 vs ⩽200)Trimester 1NoNoNo
        Landsbergis PA (1996)22PE5750.7 (0.2 to 2.5)Physical activity score (>200 vs ⩽200)Trimester 1NoNoNo
    Case–control studies
        Spinillo A (1995)48PE4802.1 (1.18 to 3.75)Activity score (moderate/high vs mild/none)Trimester 1YesNoNo
    Cross-sectional studies
        Irwin DE (1994)19PIH26651.2 (0.83 to 1.6)⩾2/3 vs ⩽1/3 of timeNot statedNoYesNo
        Irwin DE (1994)19PE26680.75 (0.52 to 1.1)⩾2/3 vs ⩽1/3 of timeNot statedNoYesNo
        Nurminen T (1989)35PIH5291.1 (0.4 to 3.2)Work with a moderate physical load vs sedentaryTrimester 3YesYesNo
        Saurel-Cubizolles MJ (1985)42PIH5913.47 (2.04 to 5.83)Activity score (2/3 vs 0/1 strenuous items)Not statedYesYesYes