Can one have periods and at the same time be pregnant?

In general no, this is not possible unless the pregnancy is an ectopic pregnancy, where the embryo implants in the fallopian tube instead of the uterus. Ectopic pregnancies are rare and require immediate medical attention.

During pregnancy, the increased levels of progesterone hormone produced by the corpus luteum and placenta, prevent ovulation.

In the absence of ovulation, there is no menstrual shedding, hence no menstrual bleeding occurs during pregnancy.