Technically yes, but the chances are relatively low. While there is always a risk of pregnancy even with birth control, PCOS (Polycystic Ovary Syndrome) does not affect the patch’s ability to prevent pregnancy. The patch is 91% effective with typical use. When starting the patch, it takes up to 7 days to become effective, so after 2 weeks of use it will be acting to prevent pregnancy.
To ensure the patch is working properly, make sure it is put on dry and clean skin (i.e., do not put lotion on prior to use), and although it is very sticky, check that it stays stuck on properly. If it falls off, replace immediately.
Also, to be extra safe against pregnancy, you may want to use another method in addition to the patch, such as a condom. Barrier methods, such as condoms, also prevent against sexually transmitted infections, while the patch alone does not.