How does the birth control pill work?

All birth control pills:

Act to suppress ovulation - but does not always succeed in doing this. What doe this mean? That "breakthrough" ovulation can occur.

Cause changes in the cervical mucus- but this doesn't always have its intended effect, which is to prevent the sperm from reaching the ovu.

Cause change in the lining of the womb- so that it doesn't grow to its proper natural thickness. If a fertilized ovum (in essence, a human embryo and therefore a human life) comes into the thinner, altered lining of the womb, the embryo cannot implant,a nd so dies. This is chemical abortion.

Slow the movement in the fallopian tubes. This sometimes results in an ectopic pregnancy.

-Love Life Magazine Volume 1 no. 2, page 15