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Physical strain: pregnancy outcome and fertility. Marja-Liisa Lindbohm Finnish Institute of Occupational Health. Potential effects of physical strain. Pronounced physical exertion may alter hormonal balance increase intraabdominal pressure decrease uterine blood flow

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Physical strain: pregnancy outcome and fertility

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Physical strain: pregnancy outcome and fertility

Marja-Liisa Lindbohm

Finnish Institute of Occupational Health

Potential effects of physical strain

Pronounced physical exertion may

  • alter hormonal balance

  • increase intraabdominal pressure

  • decrease uterine blood flow

  • affect nutritional status

Measures of physical work load in occupational reproductive studies

  • Single factors

    • Heavy lifting and load carrying

    • Prolonged standing and/or walking

    • Bending and reaching

  • Integrated measures

    • Energy expenditure, work intensity

    • Biomechanical load

    • Fatigue score

  • Surrogate measures: job title, work duties

Working conditions and risk of preterm birth: a meta-analysis (Mozurkewich et al 2000)

Physically demanding work and adverse pregnancy outcome (Mozurkewich et al 2000)

Standing, lifting and having small-for-gestational-age infant (Fortier et al 1995)

Lifting, hectic work pace and pre-eclampsia (Wergeland et al 1997)

Prolonged standing and spontaneous abortion

  • Inconsistent results on the effects of standing at work on the risk of spontaneous abortion

  • In two studies an increased risk for standing at work >8 hours/day was observed, but only in women who had a history of previous fetal loss

  • Cervical incompetence or other anatomical abnormalities or weakness may predispose these women to the effects of standing

Job strain and fertility (Hjollund et al 1998 and 2004)

  • A follow-up study on couples trying to become pregnant

  • Job strain, defined as high job demands and low job control, had no substantial detrimental effect on fertility among women

  • Analysis restricted to couples with no suspected competitive causes of reduced fertility showed reduced fertility in women with high-strain jobs

  • No association found between any semen characteristics or sexual hormones and job strain


  • Pregnant workers should avoid extremely heavy physical exertion (close to the individual's maximum capacity) in early pregnancy

  • During second and third trimester, it is wise to reduce the physical work load and ensure that there are enough rest periods

  • Continuous standing or walking during the whole workday should be avoided, at least in late pregnancy

    Ahlborg, J Occup Environ Med 1995;37:943

EU guidelines on movements and postures (COM(2000) 466 final/2)

Pregnant workers should not be exposed to

  • manual handling involving risk of injury

  • awkward movements and postures, especially in confined spaces

  • work at heights

  • long periods spent handling loads, or standing or sitting without regular exercise or movement to maintain healthy circulation

Guidelines on lifting weights (Denmark)(AT-anvisning Nr., 1998)

  • Manual handling of heavy loads may pose a risk to pregnancy

  • If the load weights more than 10-12 kg there should be a break between each lift and the total of lifted weights should not exceed 1000 kg during a day

  • From the beginning of the 7th month of pregnancy the weight of the lifted loads should be halved because of increasing lifting distance

Shift work and spontaneous abortion among midwives (Axelsson et al 1996)

Shift or night work and preterm birth: a meta-analysis (Mozurkewich et al 2000)

  • Six studies published in 1987 – 1998

  • Pooled odds ratio 1.24 (95% CI 1.06 – 1.46)

  • Analysis of three high-quality studies revealed also a weak association (OR 1.21, 95% CI 1.00 – 1.47)

  • Conclusion: shift and night work may increase the risk of preterm birth

Shift work and fetal growth retardation

  • Inconsistent results on the effects of shift work

  • Elevated risk of giving birth to SGA babies among mothers in shift work (Nurminen et al 1989)

  • Elevated risk of having a baby with low birth weight (<2500 g) among midwives in night work (Bodin et al 1999)

  • No excess of fetal growth retardation related to shift work or to evening or night work only (Fortier et al 1995)

Council Directive 92/85/EEC: night work

  • Member States shall take necessary measures to ensure that a worker is not obliged to perform night work during her pregnancy and for a period following childbirth

  • A medical certificate stating that this is necessary for the safety or health of the worker is needed

  • Measures must entail the possibility of

    • transfer to daytime work

    • or leave from work or extension of maternity leave where such a transfer is not feasible

EU Guidelines on fatigue and working hours (COM(2000) 466 final/2)

  • Because of increasing tiredness, some pregnant women may not be able to work irregular or late shifts, night work or overtime

  • Not all women are affected in the same way; the risks vary with the type of work and the individual

  • It may be necessary to adjust working hours temporarily, including the timing and frequency of rest breaks, and to change shift patterns and duration to avoid risks

Noise and adverse pregnancy outcome

  • Noise may increase maternal catecholamine secretion, which may further stimulate or retard uterine contractions and affect uteroplacental blood flow

  • Noise exposure of 85dBL has been associated with fetal growth retardation

  • An excess of hormonal disturbances, infertility and spontaneous abortion also reported

  • EU Guidelines: pregnant workers should not be exposed to noise levels exceeding national limit values

EU Guidelines on some physical agents (COM(2000) 466 final/2)

Pregnant workers should not

  • be exposed to prolonged excessive heat or cold

  • work in a high-pressure atmosphere or dive

  • be exposed to unpleasant vibration of the entire body, particularly at low frequencies

  • be exposed to work entailing shaking, shocks or where jolts or blows are delivered to the lower body

References on physical strain, shift work and reproductive health

  • Mozurkewich EL, Luke B, Avni M, Wolf FM. Working conditions and adverse pregnancy outcome: a meta-analysis. Obstet Gynecol 2000;95:623-635.

  • Nurminen T. Shift work and reproductive health. Scand J Work Environ Health 1998;24:28-34.

  • Ahlborg G. Physical work load and pregnancy outcome. J Occup Environ Med 1995;37:941-944.

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