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.
The question of how soon after you stop breastfeeding can you get pregnant is slightly complex, because you do not need to stop breastfeeding to get pregnant. You can get pregnant while you are still breastfeeding although the chances of this are slim. It is a common misconception that breastfeeding poses as natural birth control.