How long until birth control is effective?

Patient: I just started the Pill a week ago, on Monday the 5th and my partner ejaculated on the outside of my vagina, what is the chance of me getting pregnant?

Symptoms: Nothing yet

Doctor: Hello,An oral contraceptive pill has to be started from the day 1/2 of your fresh cycle as the concentration levels o f the hormones take at least a week to 10 days to reach a ovulation inhibitory level which then prevents ovulation which normally occurs in the mid-cycle.So if the pill is started after the menses end, then there are chances that contraceptive efficacy may not be established by the time of ovulation and hence ovulation would occur and leading to failure of contraceptive efficacy and increasing the chances of pregnancy if unprotected intercourse is experienced under the fertile period then.If there has been an ejaculate outside the vagina and you have dealt it responsibly then the chances o pregnancy are minimal unless there has been a pre cum ejaculated inside the vagina.It is advisable that you may continue your pills without gap and without missing them,. In case your periods are missed even on placebo pills then you may undergo a serum beta hcg test to rule out pregnancy, if resumed then you would be pregnancy safe.I hope i have answered your query in detail,wishing you good health,regards