IF you've attended a sex ed class or been given a 'birds and bees' talk, you probably have an idea of how people go about making babies.
Conception happens when sperm swims up through the vagina and fertilises an egg, usually during a precise window of the menstrual cycle.
But, as it turns out, this isn't the only way you can get pregnant.
From "splash pregnancies" to oral sex, people have managed to get pregnant in pretty implausible ways, according to professor and director of the Clinical Anatomy Learning Centre at Lancaster University, Adam Taylor.
"There are also examples of women conceiving in extremely rare circumstances that you’d expect to be impossible," Dr Taylor wrote in .
1. 'Splash pregnancies'
It's basically in the name - "splash pregnancies" can occur from semen splashing onto external genitalia.
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For this highly unlikely form of conception to occur, sperm would then need to find their way into the vagina and swim towards the ovaries.
These kinds of pregnancies are so rare, according to Dr Taylor, as "sperm don’t survive for more than half an hour outside the body".
Even under typical conditions, it can be hard for sperm to fertilise an egg in the first place, the clinical anatomy expert said.
"While healthy sperm swim at up to 5mm a minute, they only survive for a limited period of time - up to five days - in women’s genitalia," he added.
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"Of the hundreds of millions of sperm that are ejaculated into the vagina during intercourse, where conditions are ideal, only 200-300 will make it to the egg," Dr Taylor added.
He noted that you can't get pregnant from sperm in bathwater or hot tubs, as water tends to disperse the sperm and chlorine kills it.
2. Through oral sex
Getting pregnant through oral sex can be nigh impossible - but Dr Taylor pointed to a bizarre medical case report to demonstrate "sperm’s dogged ability to navigate towards the egg".
The report, , details the case of a woman born without a vagina who went to the doctors complaining of intermittent abdominal pain that felt strangely like contractions.
Doctors discovered that these were in fact labour pains, as she was pregnant, and delivered the baby via C-section.
"Given the girl was born without a vagina, this ruled out intercourse as the method of conception," Dr Taylor said.
"But precisely 278 days before, the girl had been admitted to hospital with stab wounds in her stomach.
"The wounds were the result of a knife fight between her, her jealous ex and her new partner."
The report details a truly bizarre chain of events.
The woman performed oral sex on her new male partner just before the knife fight.
"So when the surgery was done to repair her stomach wounds, it potentially washed any sperm that still existed around her abdominal cavity – allowing them to migrate towards and fertilise the ovum," Dr Taylor explained.
"Sperm in the peritoneal cavity - the space between your abdominal organs and body wall - is not unheard of.
"This cavity contains a special fluid that helps your organs move around when food is passing through.
"And research has shown this fluid can also support the survival of sperm, enabling it to travel through this cavity to the ovum."
3. Through anal sex
Most people tend to assume that you can sidestep the possibility of getting pregnant if you have anal sex.
This is true in most cases, as pregnancy from backdoor penetration is extremely rare.
But Dr Taylor explained that it can happen in people with a reproductive abnormality called a cloacal malformation, which occurs in one in every 50,000 girls.
I gave birth by myself just six minutes after realising I was pregnant
A host of symptoms will usually tip mums off to the fact that they're pregnant - not to mention the bump.
But in rare cases, what's known as a cryptic or hidden pregnancy can occur.
This is when a person isn't aware that they are pregnant until they are at least five months along, either because they're explaining away symptoms or denying them.
Some mums won't even have a noticeable bump.
This was the case for Lauren Newey, 22, who gave birth just six minutes after realising she was pregnant.
The mum woke up with stomach cramps, which got so bad she thought she might have appendicitis.
But to Lauren's shock, her waters broke - and she found herself pushing to deliver her baby.
She told The Sun: "I didn't have much time to get my head around it all. It happened so fast."
Read more on Lauren's incredible story here.
In humans, tissue grows and divides the cloaca - the “common hole” for urination, defecation and reproduction - into two or three openings, depending on your sex.
But in rare cases, this tissue doesn't completely split the rectum from the vaginal cavity.
"When this happens, it may allow sperm to swim through any opening in the dividing tissue wall towards the egg to fertilise it," Dr Taylor said.
"The fertilised egg will normally implant into the womb, as usual."
4. Superfetation
If you're already pregnant, mechanisms will usually kick in to prevent your body from becoming pregnant again.
Hormones will course through your body to prevent ovulation and produce a thick mucus that plugs the cervix and prevents sperm from entering the uterus.
"This is true even for women who are born with two uteri," Dr Taylor noted.
"But one event, called , throws those rules out the window.
"This process sees a second pregnancy manifest while the first is already progressing.
"This phenomenon is so rare that scientists don’t fully understand how it happens. Most recorded cases have been in women who used IVF."
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If this happens, you may get pregnant two to four weeks apart, often meaning the babies can be delivered together as twins.
In most cases, these pregnancies will have no complications and progress without a hitch.