As we have discussed before when describing the other pregnancy signs (please do check out our full list!), pregnancy causes an increase in the volume of blood that is pumped through your body. This is one of the factors that contributes to your beautiful skin, because more blood is circulated around your facial area too. Hormones are, of course, the other factor. Oil production working over hours on your facial skin probably sounds like a nightmare and a recipe for pimples, but this is in fact exactly what is happening to you. As a result, you will look great! The pregnancy glow is most likely to show up during your second trimester, and it might well stay with you until after you give birth.
In my experience, most women in their first trimester of pregnancy have break outs and impurities on the facial skin, and when that clears up you will be positively glowing! This is a definite pregnancy symptom, and though cosmetic companies might love to bottle that glow and sell it for lots of money, it is ultimately caused by internal things that can never be recreated when you are not pregnant. If your facial skin is too oily for your taste, you can try cleaning it with a gentle, oil-free cleanser. Of course, there is always facial powder to help you as well.