Hormone birth control, such as birth control pills, contains synthetic forms of estrogen and/or progestin. While becoming pregnant on birth control pills is rare, some women worry about the effects of their birth control on their fetuses. However, according to the Mayo Clinic, "despite the years of [using birth control pills while pregnant] happening, there is very little evidence that exposure to the hormones in birth control pills causes birth defects." In addition, the Mayo Clinic states that birth control pills do not cause a miscarriage during early pregnancy. However, they should be discontinued once the pregnancy is confirmed.
Chances of Becoming Pregnant
Hormone birth control is highly effective in preventing pregnancy. However, all forms of hormone birth control have a small margin of error. When birth control pills are used correctly---every day at the same time---less than 1 percent of users will become pregnant. However, if a woman misses a pill or it is not absorbed, such as the woman vomiting, 8 percent of users will become pregnant.
Estrogen
Combination birth control pills and extended cycle pills contain low doses of estrogen, which prevents ovulation and implantation. While the levels of estrogen are lower in newer forms of birth control pills, the estrogen is still potent. The effects of strong estrogen on a woman's body can be detrimental, which raises the question about the effect of hormone birth control on a fetus. However, the Mayo Clinic states that the estrogen in birth control pills cannot cause birth defects in a fetus.
Miscarriage
One of the fears from using a hormone birth control while pregnant is the risk of miscarriage during early pregnancy. However, that is no longer a fear. The Mayo Clinic refers to the drug diethylstilbesterol, a synthetic form of estrogen; diethylstilbesterol was later linked to cancer. While the levels of estrogen in diethylstilbesterol could cause a miscarriage, the levels of estrogen in birth control pills do not. Nevertheless, women should cease using birth control pills once they find out that they are pregnant.
