<s>[INST] hi i had unprotected sex with my girlfriend 2 weeks ago ... she is on the pill though but she had just went back on it that night after having her period and i am just wondering would that pill work for that night .... and would it be possible is she pregnant cause a bit of sperm went in .. we are always really carefull apart for that time [/INST] Hello,Thanks for asking at Healthcaremagic!I have gone through your query and I can understand your concerns.Birth control pills are highly effective and failure rate is very low.The failure rate is very low and it is approximately one in thousand.The chance for pregnancy is quite low and you don't need to worry much regarding this.You can do a UPT(urine pregnancy test) for your own reassurance.Thanks. </s>