How do contraceptives work? - NWHunter

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Contraceptives are designed to prevent pregnancy in three basic ways: they either block sperm, disable sperm before they reach the uterus, or suppress ovulation. But is one strategy better than the other? And how does each one work? NWHunter describes the mechanics behind different kinds of contraceptives.

Lesson by NWHunter, animation by Draško Ivezić.

Here's what has to happen for pregnancy
to occur after sexual intercourse.

Sperm must swim up the vagina,

through the cervical opening,

upwards through the uterus,

and into one of the two fallopian tubes.

If an egg, released during
that month's ovulation, is in the tube,

one sperm has a chance to fertilize it.

Contraceptives are designed
to prevent this process,

and they work in three basic ways.

They block the sperm,

disable sperm
before they reach the uterus,

or suppress ovulation.

Block is the simplest.

Male and female condoms prevent
sperm from coming into contact

with the vaginal space.

That barrier is also why they,
unlike other contraceptive methods,

are able to prevent transmission
of certain sexually transmitted diseases.

Meanwhile, the diaphragm,
cervical cap, and sponge

work by being placed over the cervix,
barricading the entrance to the uterus.

These contraceptives are sometimes
called barrier methods

and can be used with spermicides,

an example of
the second category, disable.

A spermicide is a chemical
that immobilizes and destroys sperm.

Today's spermicides come as foam,
cream, jelly, suppositories,

and even a thin piece of translucent film
that dissolves in the vagina.

These products can be inserted directly
into the vagina before intercourse,

or can be combined with block methods,
like a diaphragm or condom,

for added proection.

The third category
for preventing pregnancy

works by suppressing the action of an egg
maturing in the ovary.

If there isn't an egg available
in the fallopian tube,

there's nothing for sperm to fertilize.

Hormonal contraceptives,

including the pill, the patch,
the Depo shot, and the vaginal ring

all release synthetic versions of various
combinations of progesterone and estrogen.

This hormone cocktail
suppresses ovulation,

keeping the immature egg
safely sequestered in the ovary.

Synthetic progesterone also has a block
trick up its sleeve.

It makes cervical mucus too thick and
sticky for sperm to swim through easily.

There are other contraceptives that
use multiple approaches at the same time.

For example, many IUDs,
or intrauterine devices,

contain synthetic hormones
which suppress ovulation.

Some also contain copper,

which disable sperm while also making
egg implantation in the uterus difficult.

Block, disable, or suppress:

is one strategy better than the other?

There are differences, but a lot of it
has to do with how convenient

and easy it is to use
each contraceptive correctly.

For example, male condoms would be
about 98% effective

if everyone used them perfectly.

That 98% means if 100 couples correctly
used condoms for a year,

two women would get pregnant.

But not everyone uses them correctly,
so they're only 82% effective in practice.

Other methods, like the patch and pill,
are 99% effective

when they're used perfectly.

But in practice, that's 91%.

Spermicide is only 85% effective,
even with perfect usage,

and just 71% effective with typical usage.

Another important consideration in the
choice of contraceptives are side effects,

which almost exclusively affect women
rather than men.

Hormonal methods in particular
can cause symptoms like headaches,

nausea,

and high blood pressure,

but they vary from woman to woman.

That's why these methods
require a prescription from a doctor.

The choice of contraceptive method
is a personal one,

and what works best for you now
may change later.

Scientists also continue to research
new methods,

such as a male pill that would
prevent sperm production.

In the meantime,
there are quite a few options

to block sperm,

disable them,

or suppress eggs
and keep them out of reach.