Like other combined birth control pills, Portia works by changing the hormone levels in your body. Hormonal birth control can stop ovulation, which is when the ovary releases an egg every month. If there’s no egg, there’s no pregnancy. However, ovulation doesn’t stop for everyone who takes the pill, so there are other things Portia does as well.
Normally, the lining of your uterus will grow every month so that it’s easier for a fertilized egg to implant itself there. On hormonal birth control, the lining stays thin. This is also why you’re likely to experience a shorter and lighter period on Portia. Lastly, the hormones change the consistency of your cervical mucus. The thicker mucus acts as a shield against sperm. All of these things together make it very, very unlikely that you will become pregnant while taking Portia.