Ergonomics And Pregnancy

If you are a working woman and are pregnant or are thinking about becoming pregnant, the following will be of particular interest to you. This fact sheet is about pregnancy and ergonomics. Ergonomics is the science of fitting the job to the worker, rather than fitting the worker to the job. You should also be aware of the possible dangers from chemical exposures in your workplace, which can be the most harmful during the first trimester (three months) of pregnancy. The Occupational Health Clinics for Ontario Workers, Inc. can give you chemical hazard information. This factsheet is about ergonomic hazards which are a problem mainly in the last trimester (three months) of pregnancy.

   You need to understand some basic health issues before you can understand the importance of ergonomic factors related to pregnancy. Pregnancy is a normal, healthy condition during which the woman's body changes in many ways. During the first trimester (the first three months), the different parts of the baby are formed and the baby is at the greatest risk for harm. In the second and third trimesters the baby's organs develop and mature, and the size and weight increase.

Figure 1: During pregnancy the large abdomen causes the centre of gravity to move forward. A curve in the spine results causing backache and strain. From: John T. Queenan and Carrie Neber Queenan; (Eds.) A New Life, Toronto; Stoddart Publishing Co., 1989; 40.

   The body's changes during pregnancy are caused by special hormones or "chemical messengers", two of which are progesterone and estrogen. Progesterone relaxes muscles of the uterus (where the baby develops), the stomach and the blood vessels. Progesterone may also cause some unwanted effects such as indigestion, constipation, heartburn and varicose veins. The second hormone, estrogen, plays an important role in the baby's growth, as well as the woman's breast development. During the latter stages of pregnancy, the growing uterus causes pressure beneath the lungs. For this reason pregnant women often find themselves short of breath.

   Throughout the pregnancy, the muscles of the pelvis relax, softening and stretching to increase pelvic size. Several joints, especially in the spine, become less stable and show signs of separation and movement to accommodate the growing baby. The back muscles have additional strain added to them, causing some of the low back pain often experienced during pregnancy. In a non-pregnant woman the centre of gravity is located just in front of the spine and level with the kidneys. In a pregnant woman the centre of gravity is shifted forward, straining the spine and throwing the woman off balance (see Figure 1). This may cause her to throw back her shoulders, lean backward on her heels, and place additional strain on her lower back. The ligaments, which add support and strength, are weakened, so the woman relies only on the muscles of the back to stand upright. The back muscles become tight and tired, leading to low back pain. Postures that would further weaken and stretch her muscles, such as leaning forward at the waist, should be avoided during the pregnancy.