Apart from being used for clotting issues, which can be hereditary, it is prescribed for the clotting issues because estrogen rises in pregnancy and makes the blood thicker and therefore susceptible to clotting. In addition, according to my dr. Braverman (rip), it helps with immune issues as well. I don’t have any clotting issues, but for both my successful pregnancies (in my 30s), I was using Clexane.