Islam And Over Population
Abu Dawood, Kitaab al-Nikaah, 1856 hadith can be interpreted as to use contraceptive if both husband and wife agrees and has no permanant damage to organs(Scholar endorsement needed) The practice was known as Azal and it has not been prohibited by Prophet Mohammad saw. However, once life has been given to child, you cannot kill them as they have same hurmat as of grown human being.
Please also refer to the video below from 1:40:20 to 1:49:10 https://youtu.be/H6VN-tW-wGk?t=6020