Pregnancy: How Does It Happen?

For many who aren’t trying to conceive or want to wait to have kids, an unexpected pregnancy can be a very scary outcome from having unsafe sex.


It helps to know more about how it happens, to soothe your worries and help you learn just how to have safe sex. And for those who are trying to conceive, learning about what your body is doing and when it’s doing it can be a great way to make sure things go as smoothly as possible.


  • Sperm: the male reproductive cell.
  • Semen: the mixture of sperm and seminal fluid released during ejaculation.
  • Egg: the female reproductive cell, also called an ovum.
  • Fertilization: when egg meets sperm.
  • Zygote: a fertilized egg.
  • Embryo: the development stage following zygote, about three weeks after conception. This is when the internal organs form, as well as the external body structure.
  • Fetus: the development stage following embryo. This happens at around eight weeks after fertilization. The already-formed organs and structures continue to grow, sex is determinate, and movement can be felt.
  • Ovulation: the release of the egg from the ovaries.


Now, we’ve discussed anatomy previously in, “Get to Know Your Vulva.” But in that article, we didn’t talk much about the reproductive aspects of anatomy for people who have a vulva. So here’s a quick map for ye weary travelers:

uterusdiagramLet’s begin with the ovaries. The ovaries are where eggs are stored. Once per ovulation cycle (about once every 28 days), an egg, called an ovum, is released from the ovaries during ovulation down the fallopian tubes, into the uterus.

The uterus is also called the womb, and if fertilization occurs, that is where the fetus will grow. The uterine lining is a thick, wall of blood around the inside of the uterus. It is there to cushion the growing fetus. If ovulation happens and the egg is not fertilized, then the uterine lining is shed at the end of the cycle. This is often called the menses, monthly, or, most commonly, a period.

Once sperm is ejaculated into the vaginal canal, it swims up past the cervix, through the uterus, and into the fallopian tubes, where it meets up with an egg. Once the sperm breaks through, into the egg, the egg is fertilized. It travels down into the uterus where it attaches to the uterine wall. Sometimes, this implantation causes bleeding, very similar to a period.

About 50% of all fertilized eggs don’t end up implanting on the wall. They are flushed out of the body during menstruation.


The most common way that an egg is fertilized by sperm is through unprotected vaginal intercourse with a penis. When the penis ejaculates, the sperm in the semen rushes past the cervix, into the uterus, and up to the fallopian tubes in a race to fertilize the egg.


But vaginal intercourse isn’t needed to get pregnant. Pregnancy can also occur if a toy, finger, or other object that has semen on it is inserted into the vaginal canal. It can even happen during anal sex, if semen leaks from the anus into the vagina, although that is considered to be a very rare occurrence. Also, sperm can still live in the vagina for up to six days after it was put there. Which means that it is possible, however improbable, to get pregnant during period sex.

And pregnancy can also occur before ejaculation as well. The penis dribbles out pre-ejaculation when it is erect to help provide lubrication to the vagina. That pre-cum often has some traces of sperm in it, although at a much smaller rate than actual ejaculate. This is why we here at the Condom Depot Learning Center strongly advise against the pull-out method.

Artificial insemination in a way of impregnating someone without sexual contact. Often, it is used in surrogacy, or by couples who cannot have children on their own. The person who carries the child may be inseminated by doctor, or may collect the sample themselves and do it. Sometimes, an already fertilized zygote can even be implanted in the uterine lining.



Most forms of birth control prevent sperm and egg from ever meeting up. Condoms prevent semen from going past the cervix. Hormonal birth control can thicken the uterine mucous making it impossible for sperm to swim through, or, like some forms of emergency contraception, it can delay ovulation, meaning that the egg won’t leave the ovaries until enough time has passed for the sperm to die. Some forms of birth control will dislodge a zygote from the uterine lining, which is the main reason why contraception is considered so controversial.

For more information on contraception, check out our complete guide.

Seem simple? The Condom Depot Learning Center is proud to announce its Back-To-Basics campaign, answering all the questions you might have missed out on in sex ed.

[Source: Merck Manuals]


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