thanks for query.
Sex during period can cause pregnancy
1)sperm can survive for upto 5days in vagina and if ovulation occur early as 10th day chances of pregnancy there.
2)if it is not a period but it is ovulation bleeding chances of pregnancy is there.
3)if her period is irregular time of ovulation not fixed,chances of pregnancy is there.
4)delayed period and early ovulation can cause pregnancy.
5)take emergency contraceptive
as early as 72hrs.
6)always use condom.
don't worry,if period not come consult gynae.