In the past three decades there has been a large increase in the number of women employed outside the home and remaining in the workforce during pregnancy (Laughlin, 2011). Although I have previously addressed pregnancy and functional testing in the WorkSaver newsletter, I feel this subject warrants additional focus.
First of all, let me point out that I totally disagree with the permissible lift weight limits during pregnancy published by the American Medical Association (AMA, 1984)). Although it has been almost 35 years since the American Medical Association’s Council on Scientific Affairs published its report on the Effects of Pregnancy on Work Performance, these guidelines continue to influence clinical decisions and workplace policies.
According to AMA’s guidelines the following weights are listed that can be lifted with normal uncomplicated pregnancies:
- Lifting more than 23 kg (51 lbs) is permitted repetitively for the first half of pregnancy (up to Week 20) and intermittently through Week 30.
- Between Weeks 20 and 24, repetitive lifting up to 23 kg (51 lbs) is permitted. A weight limit of 11 kg (24 lbs) is specified after Week 24.
- After Week 30, intermittent lifting up to 11 kg (24 lbs) is permitted.
McDonald et al (2013) compared the National Institute for Occupational Safety and Health’s (NIOSH) recommended lifting levels (RWLs) to the AMA guidelines for lifting during pregnancy. The NIOSH lifting equation has been widely used as an ergonomic tool that quantifies safe lifting and has also been used in legal proceedings, often in an attempt to impugn an employer’s liability in causing a lifting injury. The parameters used in the NIOSH Lift Equation include:
- Horizontal reach distance
- Vertical height of the lift
- Symmetry (with respect to twisting of the spine during the lift)
- Duration of lifting
- Frequency of lifting
- Type of hand holds in the item to be lifted
McDonald’s study found that the original AMA guidelines for tolerable lift capacities during pregnancy were substantially higher than the ergonomic calculated limits using the NIOSH lifting equation. In essence, lifting guidelines published by the AMA in 1984 and by NIOSH in 1981 (revised in 1991) are incongruent. Several factors were ignored by AMA. The AMA guidelines did not define the terms repetitive and intermittent lifting, limiting their application. The NIOSH equation also did not take into account pregnancy-related physiological and physical changes that can increase overexertion risk. For example, increased antero-posterior, lateral, and rotational shear forces in the spine during symmetrical and asymmetrical lifting are totally ignored. Very importantly, both the AMA Guidelines and the NIOSH Lift Equation fail to consider evidence linking lifting demands with reproductive or developmental effects.
Of special note is that the American Conference of Governmental Industrial Hygienists (ACGIH) lifting threshold limit value restricts most lifting from the floor in its guidance for the general working population (ACGIH, 2012). Practical application of the ACGIH lifting threshold limit value after 20 weeks’ gestation would preclude lifting from the floor because abdominal protrusion would extend the distance that objects are handled in front of the body.
Additionally, research among those who are pregnant indicates that a significant majority of women entering the third trimester have difficulty in picking up objects from the floor, (Cheng, et al., 2006) and evidence by Bonzini et al (2009) and Florack et al (1993) each showed a nearly 3-fold increased risk of preterm labor and spontaneous abortion, respectively, for women whose job required bending at the waist more than 1 hour per day. McDonald et al further recommended no overhead lifting because of reports of increased task performance difficulties (Cheng, 2006) coupled with an increased risk of postural instability (Mens et al, 2012; Dunning et al, 2010) and an increased anteroposterior postural sway (Oliveira et al, 2009) because of center-of-mass (COG) changes with increased gestation that increase shear forces in the spine during spinal compression.
Although McDonald’s study indicated that the recommended weight limits (RWLs) determined by the NIOSH lift equation represent lifting thresholds that most pregnant workers with uncomplicated pregnancies should be able to perform without increased risk of adverse maternal and fetal health. The bottom line is that the FFD evaluator and the employer are taking a significant risk any time the pregnant mother has to perform lift testing. Any lifting guidelines accepted by an evaluator do not account for the effects of hormonal induced joint laxity and increasing shear forces during pregnancy.
It is opined by this author that pregnancy-related joint laxity reduces the load-bearing capacity of pregnant women. More research is certainly needed to examine joint stabilization of the spine and pelvic girdle regions during pregnancy and the postpartum period to determine whether laxity is associated with increased muscle recruitment and co-contraction, factors known to significantly increase spinal loading (Marras, 2008)
Summary
Due to the relative paucity of reliable clinical and biomechanical research related to inherent risk factors present during pregnancy when lifting, it is my opinion, and the position taken by WorkSaver, that lifting (in particular low-level lifting such as squat lifting, and overhead lifting) should not be conducted on a woman during any phase of her pregnancy. Besides the possibilities of aggravating pregnancy-related medical conditions that may not be detected at the time of lifting such as preeclampsia (Spinillo et al, 1995), low level bending should always be avoided due to higher lumbar compressive forces and increased intraabdominal pressure associated with this type of lifting. High level (overhead) lifting should be avoided due to postural instability as the COG changes during gestation. Finally, for the same reasons, repetitive or sustained bending of the trunk should be avoided. These same limitations should be applied by the employer as work accommodations until a woman is no longer pregnant and has been cleared post-partum by a medical physician. These types of accommodations are in compliance with the Pregnancy Discrimination Act (PDA).
For more information regarding this topic and WorkSaver’s policies, please call (800) 414-2174 or e-mail Dr. Bunch at dr.bunch@worksaversystems.com or Trevor Bardarson, PT, OCS, CBES, President at trevor@worksaversystems.com
References:
American Medical Association Council on Scientific Affairs. (1984) Effects of pregnancy on work performance. JAMA. 251:1995–7.
American Conference of Governmental Industrial Hygienists. (2012) Lifting. 2012 TLVs and BEIs: based on the documentation of the threshold limit values for chemical substances and physical agents and biological exposure indices. Cincinnati, OH: ACGIH Signature Publications. 177–180.
Bonzini M, Coggon D, Godfrey K, Inskip H, Crozier S, Palmer KT. (2009) Occupational physical activities, working hours and outcome of pregnancy: findings from the Southampton Women’s Survey. Occup Environ Med. 66:685–90.
Cheng PL, Dumas GA, Smith JT, Leger AB, Plamondon A, McGrath MJ, et al. (2006) Analysis of self-reported problematic tasks for pregnant women. Ergonomics. 49:282–92.
Donald, LA et al. (2013). Clinical guidelines for occupational lifting in pregnancy: evidence summary and provisional recommendations. Am J Obstet Gynecol. 2013 August; 209(2): 80–88.
Dunning K, Lemasters G, Bhattacharya A. (2010) A major public health issue: the high incidence of falls during pregnancy. Matern Child Health J. 14:720–5.
Florack E, Zielhuis G, Pellegrino J, Rolland R. (1993) Occupational physical activity and the occurrence of spontaneous abortion. Int J Epidemiol.22:878–84.
Laughlin, LL. (2011) Maternity leave and employment patterns of first-time mothers: 1961–2008.
Washington, DC: US Department of Commerce, Economics and Statistics Administration, US Census Bureau.
Marras WS. (2008). The working back: a system view. Hoboken, NJ: Wiley-Interscience.
Nicholls JA, Grieve DW. Performance of physical tasks in pregnancy. Ergonomics. 35:301–11.
Mens JM, Huis in ‘t Veld YH, Pool-Goudzwaard A. (2012) Severity of signs and symptoms in lumbopelvic pain during pregnancy. Man Ther. 17:175–9.
Oliveira L, Vieira T, Macedo A, Simpson D, Nadal J. (2009) Postural sway changes during pregnancy: a descriptive study using stabilometry. Eur J Obstet Gynecol Reprod Biol.147:25–8.
Spinillo A, Capuzzo E, Colonna L, Piazzi G, Nicola S, Baltaro F. (1995) The effect of work activity in pregnancy on the risk of severe preeclampsia. Aust N Z J Obstet Gynaecol. 35:380–5.
Waters, T., MacDonald, L., Hudock, S. & Goddard, D. (2014). Provisional Recommended Weight Limits for Manual Lifting During Pregnancy. Human Factors, 56 (1): 203–214.