The rib muscles were used in a study of tummy pressure during a push whilst giving birth. The ribs were found to be significant in the amount of pressure recorded in the tummy. Adjusting the thorax could improve your co-ordinated pushing during your delivery. I have found in practice that the pressure of the thorax and pressure of the tummy are related. Sometimes when a chiropractor adjusts a different part of your body to that which you were expecting they may be looking to improve the co-ordinated efforts of your body. Giving birth need not lead to a loss of bladder control.
Demaria F et al (2004) Intercostal EMG to Quantify Maternal Expulsive Efforts during Pregnancy. Neurology and Urodynamics J 23 675-678