An attempt was made to determine the effect of pregnancy on the abdominal muscles and to correlate changes in abdominal muscles strength with low-back pain during pregnancy. The study included 328 women. Group A consisted of 164 pregnant women; group B consisted of 164 non-pregnant women. The race, age, height, weight, parity, profession, time devoted to physical fitness per week, abdominal length, and relation between the abdominal length to height were recorded. A detailed history relating to backache prior to and during pregnancy was obtained. Each woman was asked to perform a single sit-up. The results of the study indicate that about 10% of pregnant women develop severe low-back pain that interferes with daily life activities. About 49% of the non-pregnant women complained of LBP. The pain did not interfere with activities of daily living. During pregnancy, due to overstretching of the abdominal muscles, the ability to perform a sit-up is significantly decreased. Whereas all non-pregnant women could perform a sit-up, 16.6% of pregnant women could not perform a single sit-up. There was no statistically significant correlation between the sit-up performance and backache. It may be concluded that during pregnancy the abdominal muscles become insufficient.