4 Rare Ways Pregnancy Can Happen Without Intercourse

Unless you missed sex education at school, you will probably understand the basics of how babies are conceived. For pregnancy to occur, an egg (ovum) must be fertilised by sperm during a specific point in the menstrual cycle.

Sexual intercourse creates the best conditions for reproduction. However, not every pregnancy begins in this way.

In exceptionally rare situations, women have conceived in circumstances that might seem impossible.

1. Through anal sex

Pregnancies following anal sex are extraordinarily uncommon, but they have occurred. All documented cases have involved people with a reproductive condition known as a cloacal malformation.

This condition affects one in every 50,000 girls and requires corrective surgery. Even after surgery, there remains a substantial likelihood of complications, including renal failure, incontinence, difficulties becoming pregnant and a higher risk of early labour.

A cloaca is a "common hole" used for urination, defecation and reproduction. It is normally found in reptiles, birds and even platypuses.

In humans, tissue develops downwards and separates the cloaca into two or three openings, depending on sex. In rare instances, however, that tissue does not fully divide the rectum from the vaginal cavity.

In this situation, sperm may be able to pass through openings in the tissue wall that separates them, travelling towards and fertilising the egg. As usual, the fertilised egg would generally implant in the womb.

You may wonder why sperm do not simply continue up the rectum. The reason is that they use chemotaxis, which enables them to detect tiny traces of chemicals produced by the ovum.

As sperm move closer to the ovum, they detect increasing quantities of these "chemoattractants", which tells them that they are moving in the correct direction.

2. Through oral sex (and one very heated argument)

Sperm's persistent capacity to find an egg is perhaps best illustrated by one of the most unusual case reports in medical literature.

A young girl who had been born without a vagina sought medical help for occasional abdominal pain that, in many respects, resembled contractions.

Doctors carried out further examinations and found a foetus in her uterus. Her pain was occurring because she was in labour, and the baby was delivered immediately by C-section.

Because the girl had been born without a vagina, intercourse could be excluded as the route of conception. Yet exactly 278 days earlier, she had been hospitalised with knife wounds to her stomach. She had received those injuries during a knife fight involving herself, her jealous ex and her new partner.

It emerged that, shortly before the fight, she had performed oral sex on her new partner.

When surgery was performed to treat her stomach wounds, it may have washed sperm still present around her abdominal cavity, enabling them to travel towards and fertilise the ovum.

The presence of sperm in the peritoneal cavity - the space between the abdominal organs and the body wall - is not unprecedented.

This cavity contains a particular fluid that lets organs move as food passes through the body. Research has also shown that this fluid can help sperm survive, allowing it to travel through the cavity towards the ovum.

3. Splash pregnancies

A "splash pregnancy" is another means by which someone can become pregnant without having intercourse.

As the term implies, if semen splashes onto the external genitalia, sperm can potentially enter the vagina and swim towards the ovaries.

Splash pregnancies are very unlikely. Sperm do not live for longer than half an hour outside the body. Although healthy sperm can swim at speeds of up to 5 mm per minute, they survive only for a limited time - up to five days within women's genitalia.

Of the hundreds of millions of sperm ejaculated into the vagina during intercourse, where conditions are ideal, just 200-300 reach the egg. This makes it clear why a splash pregnancy is so unusual.

A splash pregnancy cannot result from sperm in bathwater or hot tubs. Water spreads the sperm and dilutes the seminal fluid that would ordinarily shield sperm from a woman's harsh internal genitalia and from the outside environment. Chemicals in water, including chlorine, also kill sperm quickly.

4. Double pregnancy

The body has systems that stop another pregnancy occurring when a woman is already pregnant. This also applies to women born with two uteri, as these mechanisms act strongly to prevent a second pregnancy.

Hormones stop ovulation, while a thick mucus plug forms over the cervix to prevent sperm from entering the uterus and travelling towards the ovary.

However, an event known as superfetation defies these rules. In this process, a second pregnancy develops while the first pregnancy is already under way.

The phenomenon is so uncommon that scientists do not completely understand how it occurs. Most reported cases have involved women who used IVF.

The pregnancies commonly begin close together, generally within two to four weeks of each other. Consequently, the babies may be delivered together as twins.

Despite the difference in gestational age, most of these pregnancies proceed normally, with no complications beyond those more generally seen.

Naturally, these examples are exceptionally rare, so there is probably little reason to be overly concerned. But if you do not want to become pregnant soon, make sure you use contraception.

Adam Taylor, Professor and Director of the Clinical Anatomy Learning Centre, Lancaster University

This article is republished from The Conversation under a Creative Commons license. Read the original article.