I'm on birth control [mircette] and i was wondering can you get pregnant in the first week of taking it?

Yes: It is generally advised to use some form of back-up birth control for at least the first 2 weeks of starting a birth control pill. I often advise patients to wait for the first period to be sure that the dose of the ocp is enough. If you're having "breakthrough" bleeding mid-cycle there is some risk of "breakthrough" ovulation, as well. At 45 you may want to consider a non-estrogen birth control.

Possible: A low dose ocp such as Mircette (ethinyl estradiol and desogestrel) has 20 mcg of ethinyl estradiol. If you are a new start user, we usually recommend a back-up method (condoms or abstinence) for at least the first 2 weeks. It is possible to get pregnant if you start taking the pill close to your ovulation time. Check a pregnancy test if you don't have a menstrual cycle after your first pack. Good luck.