The abortion-breast cancer (ABC) hypothesis (also known as ABC link) posits a causal relationship between induced abortion and an increased risk of developing breast cancer. In early pregnancy the level of estrogens increases, leading to breast growth in preparation for lactation. The abortion-breast cancer hypothesis proposes that if this process is interrupted with an abortion – before full differentiation in the third trimester – then more relatively vulnerable undifferentiated cells could be left than there were prior to the pregnancy, resulting in a greater potential risk of breast cancer.