The combination of high estrogen and progesterone
levels suppresses further ovulation
during pregnancy. Progesterone also encourages the growth of milk-producing glands in the breast during pregnancy.
High progesterone levels are believed to be partly responsible for symptoms of premenstrual syndrome (PMS), such as breast tenderness, feeling bloated, and mood swings. When you skip a period, it could be because of failure to ovulate and subsequent low progesterone levels.