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.
Moreover, caffeine is diuretic and causes dehydration, and it is important to be hydrated particularly while nursing. Thus, it is advisable to limit caffeine consumption while breastfeeding with not more than two or three cups of tea, coffee, or caffeine beverage each day (4). In the US, not more than 200 mg caffeine a day is recommended for breastfeeding mothers. It comes to about two mugs of tea or one mug of filter coffee or two mugs of instant coffee, a day. NHS recommends that you have caffeine drinks occasionally, rather than every day, if your baby is young.