Doctors would ease pain with medications and sometimes shorten the labour by using forceps. Both these interventions confined women to their beds, usually lying on their back most of the time. Being in bed also made it easier for the doctor to see what was happening and to intervene if necessary, which they frequently did. It wasn't long before these procedures spread routinely throughout the Western world and is often the scene you will see on TV and in films today.
We now know that laying flat on your back isn't the best position to birth your baby and we are very lucky that our healthcare providers support this in a normal birthing situation. Many hospitals and antenatal classes will advise against using this position and recommend alteratives, such a squatting (the optimum position) and being on all fours. The poster here provides some great illustrations of alternate positions.