Dear student, Lactational amenorrhea: It is the absence of menstruation during lactation. So, in the lactation period, the chances of conception are almost zero.Periodic abstinence is a natural method of birth control in which the couples avoid or abstain from coitus from day 10 to 17 (fertile period) of the menstrual cycle, when ovulation could be expected and by doing so conception could be prevented. Thanks and regards