The genotype of the mother and the fetus influences the efficacy of a teratogen. For example, genotype determines the prevalence of cleft palate in inbred strains of mice whose mothers are administered cortisol during pregnancy.
Most women will not start ovulating in the first six weeks after giving birth.1 Breastfeeding typically delays the onset of ovulation.2 Depending on the intensity of breastfeeding, it can be several months or over a year before you regain your fertility.
If they don't breastfeed, most women begin to ovulate again about four to six weeks after having their baby. Ovulation can occur before a woman has her first period after childbirth. Women who breastfeed usually don't begin to ovulate again until five to six months after the baby is born. Every woman is different, however, and ovulation may begin again at different times. To avoid an unwanted pregnancy, use birth control after having a baby even if you haven't started having your period again.