Standard birth control does not kill a fetus or end an established pregnancy. Hormonal contraceptives like the pill, patch, ring, and IUD work by preventing pregnancy from occurring in the first place, primarily by stopping ovulation. If you’re already pregnant, taking birth control pills will not terminate the pregnancy or harm the fetus. This is one of the most common points of confusion around contraception, and the science is clear.
How Birth Control Actually Prevents Pregnancy
Hormonal birth control works through several layers of defense, all aimed at preventing fertilization. The estrogen in combination pills suppresses the hormonal signals that trigger ovulation each month. No egg released means no pregnancy. Progestins, found in all hormonal methods, thicken the cervical mucus so sperm can’t easily reach an egg and interfere with the chemical changes sperm need to penetrate an egg.
Some medical references list “inhibiting implantation” as an additional theoretical mechanism, meaning the uterine lining could become less hospitable to a fertilized egg. This is where much of the concern originates. However, research on emergency contraceptives (which use higher doses of the same hormones) has found that these drugs are ineffective at preventing pregnancy once ovulation has already occurred. This strongly suggests that blocking implantation is not a significant real-world mechanism. The primary action is preventing ovulation and fertilization.
What Happens If You Take the Pill While Pregnant
A large Danish study tracking over 880,000 live births found no increase in birth defects among babies whose mothers used oral contraceptives right up to or even after the point of conception. The rate of major birth defects was virtually identical across all groups: 25.1 per 1,000 births among women who never used the pill, and 24.8 per 1,000 among women who used it after pregnancy onset. The adjusted risk showed no statistically significant difference.
The American College of Obstetricians and Gynecologists states directly that hormonal emergency contraception poses no risk to an established pregnancy or a developing embryo. For women who have a breakthrough pregnancy while on the pill, or who become pregnant shortly after stopping, the exposure is unlikely to cause birth defects.
Birth Control Is Not the Same as Abortion Medication
The confusion sometimes stems from conflating birth control with medication abortion. These are pharmacologically different. Medication abortion uses a progesterone blocker combined with a drug that causes uterine contractions. This combination is specifically designed to end a pregnancy up to 9 to 13 weeks. Birth control pills contain synthetic versions of estrogen and progesterone that support the body’s existing hormonal cycles to prevent ovulation. They do not block progesterone’s action, and they do not cause uterine contractions.
The morning-after pill (Plan B) also does not end a pregnancy. It contains a higher dose of the same progestin found in regular birth control pills, and it works by delaying or preventing ovulation. If ovulation has already happened and fertilization has occurred, Plan B will not disrupt the pregnancy. As the Cleveland Clinic puts it: “The morning-after pill doesn’t end a pregnancy; it prevents pregnancy from happening.”
Ella Works Differently but Still Does Not End Pregnancy
Ella (ulipristal acetate) is a prescription emergency contraceptive that belongs to a class of drugs called selective progesterone receptor modulators. Because it interacts with progesterone receptors, some have questioned whether it could interfere with implantation or harm an embryo. The research suggests it does not. A review of clinical and laboratory evidence found that at the dose used for emergency contraception, Ella does not appear to have a direct effect on the embryo or prevent implantation.
In lab studies comparing Ella to the abortion drug mifepristone, mifepristone significantly suppressed embryo attachment to uterine tissue while Ella did not. Miscarriage rates among women who conceived after taking Ella were 13.6%, which is no different from the background miscarriage rate in the general population. Animal studies also showed no effect on early embryo development.
What About IUDs and Pregnancy
IUDs are among the most effective contraceptives, but on rare occasions pregnancy does occur with one in place. In this situation, the IUD itself can pose risks to the pregnancy, though not because it’s “killing” the fetus in the way the question implies. The physical presence of the device in the uterus creates complications.
A study comparing outcomes found that when the IUD was left in place, the combined rate of adverse outcomes (miscarriage, fetal growth problems, preterm birth) was 63.3%, compared to 36.8% when the IUD was removed early. The risk was especially high when the IUD sat in a low-lying position: miscarriage and adverse outcomes jumped from 16.9% in the removal group to 66.7% when the device was retained. A meta-analysis confirmed that removing an IUD after a pregnancy is diagnosed reduces the odds of miscarriage and bleeding during gestation.
This is why doctors typically recommend removing an IUD as soon as pregnancy is confirmed, as long as the strings are visible and removal is straightforward.
A Note on Older Progestins
One historical footnote is worth mentioning. In the 1950s and 1960s, early synthetic progestins derived from testosterone were prescribed during pregnancy to prevent miscarriage. These older compounds caused masculinization (virilization) in over 400 female newborns and were linked to certain genital abnormalities in male infants. These drugs are not the same as modern birth control hormones, and they were given in much higher doses with the explicit intent of sustaining pregnancy. Modern oral contraceptives use different formulations, and the large-scale evidence from current studies shows no increased risk of birth defects from today’s pills.