Since I became pregnant 4 months again I have been struggling with acne on my chest and back. Two factors that make acne more prevalent with pregnancy are the hormone, progesterone, and changes in hydration.
Progesterone is the hormone that makes the bed of implatation healthy for the fertilized egg.
The ovary makes it, but after the first trimester it is usally the placenta that makes it. Besides making implantation stable, it also relaxes smooth muscle, which prevents premature labor, but also causes constipation. It loosens up the joints, especially the pubic joint which makes more room for the baby to fit through on the way out during labor. Hydration is tough to keep up with when you're pregnant. But drinking about 6-8 glasses of water a day will not only dilute out secretions to improve acne, but will also contribute to the relaxation of the uterus and even help with the constipation.