Contraception, with a variety of methods available many people are able to avoid
unintended pregnancies. But what happens when things don’t go quite as planned?
Thanks to modern science a second chance is possible. So how does emergency
contraception or ‘plan-b’ work? And what exactly is happening inside the female
body? During the female menstrual cycle many hormones are released
beginning a chain reaction. The pituitary gland in the brain releases FSH
which stimulates the growth of follicles and a premature egg in the ovaries.
These follicles then release estrogen
which helps prepare the uterus lining and triggers the brain to release leutinizing
hormone or LH. LH then triggers ovulation in which the egg is
released into the fallopian tubes where it will spend around twelve to twenty-four
hours waiting to be fertilized. If the egg isn’t fertilized in this time it
begins to dissolve and is shed away with the uterine lining during menstruation.
Though this window of opportunity is brief it’s increased by the fact that sperm
can live for up to five days.
So the keen sperm from days ago show up early to the show anxiously awaiting
Birth control pills taken on a regular basis modify these hormone levels. By
increasing progestin levels the body thinks it’s already released an egg or
It effectively decreases FSH and LH and the cycle halts. But in the case
of emergency contraception which is only taken if regular contraception methods
a few different mechanisms take place. The most important thing to understand
is that fertilization doesn’t happen immediately or even within hours after
intercourse. Instead the sperm must undergo a few biological changes in the
fallopian tube first which takes time. This is why emergency contraception is
still possible the morning after.
It can actually work up to five days after intercourse. If taken during the
first half of the menstrual cycle, emergency contraception works
specifically to prevent ovulation.
This way the egg is not released even though it may be ready and the available
sperm cannot fertilize it.
In cases where it’s too late to inhibit ovulation
emergency contraception is thought to also thicken cervical mucus trapping sperm.
As well, it may directly inhibit fertilization between sperm and egg.
Clinical studies show that emergency contraception prevents pregnancy
before fertilization. No studies have shown an effect from emergency
contraception if fertilization has already occurred. It does not stop
implantation from happening nor does it have any effect after implantation has
In this way, its unable to cause an abortion.
And while there are some minor side effects to these drugs, such as nausea and headaches,
scientific studies have demonstrated its safety in women of all ages and found
that the benefits far outweigh any risks. Got of burning question you want answered?
Ask it in the comments or on facebook and twitter, and subscribe for more weekly science videos.
B计划的科学 - 紧急避孕