Acne is mostly caused because of the fluctuations in the hormonal levels. Pregnancy is one such stage where there is a drastic change in the hormonal level of the body, which aggravated the sebaceous glands of the body to produce excess oil, which gets trapped in the pores of the skin with dirt, pollutants, dead skin cells etc. However, the situations may be different for each and every woman.
Some women may experience an increase in the androgen level, which stimulates the formation of acne while some may experience an increase in the estrogen level, which reduces and in fact clears the skin of such acne if you already had it.
Whatever be the situation, it usually settles after the first trimester as your body goes through a lot of changes during that period. And if you acquire acne during your pregnancy it usually fades after the first few months post delivery. During pregnancy it is always good to consult your dermatologist and gynecologist regarding any medication/treatment (whether over the counter or oral).
As some oral antibiotics and prescription drugs may be harmful to the fetus like isotretinoin (Accutane and Retinoids), which causes certain birth defects like heart, central nervous system disorder and tetracycline which cause some bone defect and discoloration of teeth. Hence, all these treatments are not prescribed to those women who are or intend to get pregnant in the near future.
Some of the measures that can be taken to treat acne at home are the application of the paste of a ripe tomato on the face and washing it off after it dries. Toothpaste too is a wonderful and effective substance used in order to treat acne. Apply it at night; the acne would be gone by morning! Lime and aloe vera are known for their antibacterial properties. Apply a mixture of lime with cinnamon on the affected area; the juice of aloe vera too would be helpful.
Always keep your body hydrated and exercise on regular basis in order to improve the circulation of blood to your body. Include fresh vegetables and fruits in your diet. Wash your face with an oil free cleanser and use an oil free moisturizer. Also, if you use an astringent see that it is non-medicated.