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Unless you skipped your sex ed class, you probably have at least a basic understanding of how a baby is formed.
The egg needs to be fertilized by sperm during a specific window in the menstrual cycle for conception to occur.
Sexual intercourse provides ideal conditions for reproduction. But that doesn’t mean that every pregnancy will occur.
There are also examples of women getting pregnant under extremely rare circumstances where you would think it was impossible.
1. For anal sex
Although pregnancies resulting from anal sex are extremely rare, they do happen. But they only occur in people with a reproductive abnormality called a cloacal malformation.
This abnormality affects one in 50,000 women and requires corrective surgery.
Even so, there is a high risk of complications such as kidney failure, urinary incontinence, difficulty conceiving, and increased risk of premature birth.
The cloaca is the “common orifice” for urination, defecation, and reproduction. Typically, it is found in reptiles, birds, and even platypuses.
In humans, this tissue grows and divides the cloaca into two or three openings, depending on the sex. However, in rare cases, this tissue fails to completely separate the rectum from the vaginal cavity.
When this happens, sperm can swim through any openings in the wall of the mitotic tissue to reach the egg, fertilize it, and, as usual, the fertilized egg usually implants in the uterus.
If you’re wondering why the sperm can’t just keep swimming through the rectum, it’s because they work by chemotaxis. This means they’re able to detect traces of chemicals released by the egg.
As sperm swim toward the egg, the amount of a “chemical attractant” they detect increases, which is an indicator that they are continuing to move in the right direction.
2. Through oral sex
There is perhaps no better demonstration of the sperm’s tenacious ability to swim to the egg than one of the strangest case studies recorded in the medical literature.
A young woman who was born without a vagina goes to her doctor complaining of intermittent abdominal pain that in many ways resembles uterine contractions.
Later, doctors’ examination revealed that there was a fetus in her uterus and she was in pain due to labor.
The baby was immediately born via cesarean section.
As the young woman was born without a vagina, sexual intercourse as a method of conception had been ruled out. However, just 278 days earlier, she had been admitted to hospital with stab wounds to her abdomen. These injuries were caused by a knife fight between her, her jealous ex and her new partner.
It was revealed that she performed oral sex on her new partner shortly before the fight.
So when she had surgery for her stomach injury, sperm still resisting around her abdominal cavity could have penetrated, allowing them to migrate to the egg and fertilize it.
It is not unheard of for sperm to be present in the peritoneal cavity, the space between the abdominal organs and the body wall. This cavity contains a special fluid that helps organs move when food passes through it.
Research suggests that the fluid also helps sperm survive, allowing them to pass through the cavity to reach the egg.
3. Pregnancy through water splashing
A “temporary pregnancy” is another way a woman can become pregnant without having sexual intercourse.
As the name implies, if semen splashes onto the external genitalia, sperm can enter the vagina and swim to the ovaries.
This type of pregnancy is unlikely, as sperm cannot survive outside the body for more than half an hour. Although healthy sperm can swim at a speed of up to 5 millimeters per minute, they can only survive for a limited time (up to five days) in the female genitalia.
Of the hundreds of millions of sperm that are ejaculated into the vagina during intercourse, only 200 to 300 reach the egg when conditions are ideal. You can understand why splash pregnancies are so rare.
However, it is not possible to get pregnant by splashing sperm into bath water or a hot tub, as the water disperses the sperm and dilutes the seminal fluid that normally protects the sperm from the acidity of the vagina and the outside world.
Chemicals present in water, such as chlorine, can also quickly kill sperm.
4. Twin pregnancy
When a woman is already pregnant, the body has a mechanism to prevent another pregnancy.
This is true even for women who are born with two uteruses, as the mechanisms work to prevent a second pregnancy.
The hormones prevent ovulation and produce a thick mucus plug that covers the cervix, preventing sperm from traveling to the ovaries.
But a phenomenon known as “cult” throws those rules out the window.
This process can result in a second pregnancy occurring at the same time as the first.
The phenomenon is so rare that scientists don’t fully understand how it happens. Most documented cases have occurred in women undergoing in vitro fertilization.
The two pregnancies tend to be very close together, usually two to four weeks apart, which means the babies can be born at the same time, making them twins.
Despite the variability in gestational age, most pregnancies progressed normally without complications, except for more widely observed conditions.
Of course, these cases are extremely rare, so you probably don’t need to worry too much. But if you’re not planning on getting pregnant anytime soon, make sure you’re using birth control.
By Adam Taylor
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*Adam Taylor is Professor and Director of the Clinical Anatomy Learning Centre at Lancaster University, UK.
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