Physical strain: pregnancy outcome and fertility

1
Physical strain pregnancy outcome and fertility

• Marja-Liisa Lindbohm
• Finnish Institute of Occupational Health

2
Potential effects of physical strain

• Pronounced physical exertion may
• alter hormonal balance
• increase intraabdominal pressure
• decrease uterine blood flow
• affect nutritional status

3
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

4
Working conditions and risk of preterm birth a
meta-analysis (Mozurkewich et al 2000)
Exposure No. studies Pooled odds ratio 95 CI
Standing ?3 hours/day 14 1.26 1.13 1.40
Physically demanding work 21 1.22 1.16 1.29
Long working hours (?40 h/w or ?8 h/d) 10 1.03 0.92 1.16
High cumulative work fatigue score 6 1.63 1.33 1.98
5
Physically demanding work and adverse pregnancy
outcome (Mozurkewich et al 2000)
Pregnancy outcome No. studies Pooled odds ratio 95 CI
Small for gestational age 10 1.37 1.30 1.44
Hypertension or preeclampsia 4 1.60 1.30 1.96
6
Standing, lifting and having small-for-gestational
-age infant (Fortier et al 1995)
Exposure Number of women Adjusted odds ratio 95 CI
Standing lt 3 2160 1.00 .
3 5 hours 888 1.13 0.83 1.55
? 6 hours 1342 1.42 1.02 1.95
Lifting, none 2500 1.00 .
1 9 kg 876 1.03 0.77 1.38
? 10 kg 578 1.03 0.71 1.51
7
Lifting, hectic work pace and pre-eclampsia
(Wergeland et al 1997)
Exposure Number Adjusted OR 95 CI
Lifting 10-20 kg
gt20 times weekly 279 2.0 1.2 3.2
10 - 20 times daily 307 1.7 1.1 2.7
gt20 times daily 196 1.4 0.8 2.6
Hectic work pace
Not daily 1992 1.5 0.8 2.9
Daily lt half the time 513 2.1 1.0 4.2
Daily gt half the time 443 2.5 1.2 4.9
8
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 gt8 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

9
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

10
Recommendations

• 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 199537943

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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

12
Guidelines on lifting weights (Denmark)(AT-anvisn
ing Nr. 4.0.0.2, 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

13
Shift work and spontaneous abortion among
midwives (Axelsson et al 1996)
Exposure Preg- nancies Adjusted OR 95 CI
Always day 422 1.0
Always night 286 1.6 1.0 2.8
Two shift 638 1.2 0.7 1.8
Three shift 371 1.5 0.9 2.6
Late spontaneous abortion Always night 285 3.3 1.1 9.9
14
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

15
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 (lt2500 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)

16
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

17
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

18
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

19
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

20
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 200095623-635.
• Nurminen T. Shift work and reproductive health.
  Scand J Work Environ Health 19982428-34.
• Ahlborg G. Physical work load and pregnancy
  outcome. J Occup Environ Med 199537941-944.