When someone gets pregnant while on birth control and then continues taking it daily until realizing they are pregnant, how does this not harm the fetus? Are there notable side effects from this?
The active ingredients in birth control pills are estrogen and progesterone…two hormones that would be present in the female body anyway. The pill works by elevating your hormone levels to mimic pregnancy levels. (this is what prevents you from ovulating.) In a healthy pregnancy, your levels of estrogen and progesterone steadily increase throughout the pregnancy anyway. These hormones do a lot of the heavy lifting during fetal development, so they are not in and of themselves harmful to the fetus. There can be side effects from taking the pill during pregnancy, however. While it is not known to increase the risk of congenital defects, it may increase the risk of premature birth or miscarriage (or at least there appears to be a correlation in certain studies.)
Birth control are synthetic *Progestins* AKA Progestogens that trick the body into thinking it’s already pregnant.
Normally progestins are produced by the ovaries and uterus in response to the complex ballet of events that occurs during implantation and early pregnancy.
Progestins have several effects. It interferes with the development and release of Ova, a.k.a. egg cells, although doesn’t, in practice, stop it. It also causes the cervical mucus to thicken making it very difficult, though not impossible for sperm to enter the uterus.
Progestins also have numerous other effects on the body, but these are the two effects most relevant.
The point of this is essentially push pause on the normal ovulation cycle while the fetus is developing, so you don’t end up with a second, concurrent fetus several months later. That would mean labor would not only certainly be fatal to the second fetus, but would present an additional risk to the mother, while using up blood supply and nutrients.
This doesn’t generally effect an embryo that has already implanted.
Indeed, levels of progesterone and other related natural progestins would begin to rise already after implantation, in response to the production of HCG by the embryo, which is the hormone that pregnancy tests detect. In that case increased progestins in the body are actually beneficial by improving the quality of them endometrial lining of the uterus.
Most birth control works by increasing levels of hormones that tell the body it is pregnant already, basically fooling it.
Those hormones would, by necessity, be present during a real pregnancy. A fetus is expected to be exposed to them.
Birth control pills aren’t some anti-baby poison.
As far as we can tell this does not cause any harm at all. The female birth control pills is essentially designed to mimic the natural bodies hormones when pregnant. So if you get pregnant anyway you are just doubling up on your dose. Kind of like having twins.