2nd STAGE OF LABOUR
This is the period from full dilatation of the os uteri to the birth of the baby.
Physiological changes which take place are concerned with the descent of the foetus through the birth canal and its expulsion.
In addition to uterine contractions, a bearing down force on the part of the mother to overcome the resistance of the soft parts, vagina, pelvic floor and external parts.
Contractions are expulsive, occur every 2-3 minutes and last for 60-70 seconds.
There is marked retraction of the uterus which aids descent of the foetus through the birth canal.
Force of uterine contractions and secondary powers is transmitted down the foetal spine to its head this is called foetal axis pressure and helps descent of the foetus through the birth canal.
Expulsion of the foetus is further aided by voluntary muscles of the diaphragm and abdominal wall.
When 2nd stage is reached, woman compelled to push, as she holds her breath to push, diaphragm is lowered and abdominal muscles contract.
These secondary powers increase expulsive force of uterine contractions
DISPLACEMENT OF THE PELVIC FLOOR
Advancing foetus distends the vagina and pelvic floor.
Anteriorly the pelvic floor is pushed up, and the bladder is drawn up into the Abdomen.
Posteriorly, pelvic floor is pushed down in front of the presenting part.
Rectum is compressed; any faecal contents will be expelled.
Perineal body becomes elongated and paper-thin as it is flattened by the foetus.
EXPULSION OF THE FETUS
It is accompanied by marked retraction of the uterus which starts the process of placental separation.