31 surprising things you may not know about pregnancy

It's no secret that pregnancy changes the human body. When a woman carries a child, her body has to go through many adjustments to make sure she and the baby get through the next nine months (or thereabouts) safely.

Her organs will have to shift around to make space for the baby, but there are many other subtle changes that aren't obvious at first glance.

The foetus also goes through remarkable changes while it grows in the womb, and may be more aware of what's happening in the outside world than you realise.

Here are 31 surprising facts about pregnancy, and some of the explanations for why the human body changes so much during that time.

1. The uterus gets a lot bigger

Before pregnancy, a woman's uterus is typically the size of an orange. By the third trimester, it can be about the size of a watermelon. In fact, it can expand up to 500 times the size during pregnancy.

2. The longest pregnancy ever recorded was 375 days long

The longest time on record that someone has been pregnant for is 375 days. Normally, pregnancy lasts around 280 days, so Penny Diana Hunter's baby was nearly a hundred days overdue in 1945.

Longer pregnancies are more common than you might think. Many women report being pregnant for 10 or 11 months, rather than the usual nine.

3. And the shortest was 21 weeks four days

The earliest premature baby to survive was in the womb for just 21 weeks and four days. The child, who started preschool last year, apparently has no health or developmental problems as a result of being born early.

4. A pregnant woman's blood volume increases by 40-50%

When pregnant, blood volume increases as much as 50% to help supply enough oxygenated blood to the foetus.

5. Your heart grows bigger while you're pregnant

To help pump all that extra blood around the body, the heart has to increase in size.

6. So do your feet

Many women also report that their feet got bigger while they were pregnant — as much as a whole size bigger. Ankles and feet can also swell up.

7. Your voice can change during pregnancy

With all the hormones coursing around a pregnant body, it's not surprising that there would be some changes. Another is that the voice can change. The rise in oestrogen and progesterone can cause swelling of the vocal folds, meaning some higher notes are lost and lower ones might appear.

8. Babies can hear their mother's voice from inside the womb

At about 18 weeks, a foetus is able to hear sounds. By 25-26 weeks, it is more responsive to noises and responds in the womb.

9. Some pregnant women develop diabetes

Gestational diabetes is when a pregnant person's blood sugar is too high, and the pancreas can't keep up with supplying enough insulin. It usually disappears after giving birth.

10. Your joints loosen during pregnancy

During pregnancy, the body produces a hormone called relaxin that softens ligaments — the tissues that connect your joints. This is to help make the pelvis more flexible during childbirth.

11. Your sense of smell can change

Pregnant women usually experience a heightened sense of smell in the first trimester — which can be a sign that you're pregnant in the first place. It may be an evolutionary way to help pregnant women avoid unsafe foods.

12. Parts of you may change colour

As a pregnant body changes, it can develop stretch marks, which are usually paler than normal skin. Women can also get melasma, which causes dark splotchy spots to appear on the face. The line down the stomach, called the linea nigrea, also gets darker.

The vagina can change colour too. Some women report it turning purple or blueish, which is known as Chadwick Sign. About 10% of women also get blue varicose veins appearing down there, but they should disappear a few weeks after the delivery.

13. Certain genes mean you can't get pregnant

After a year of trying to conceive, a couple is technically infertile — although that doesn't mean they won't ever have a baby. Sometimes, though, genetics mean a couple will never make a child of their own.

A chromosomal disorder called Turner syndrome affects some women. This means they have just one X chromosome rather than two, so she cannot reproduce.

A common cause of male fertility is a mutation of the CFTR gene, which causes Congenital Bilateral Absence of the Vas Deferens (CBAVD). This means sperm cannot leave the testes on their own, but luckily, treatments can help men to father children.

14. Your blood group could also have an impact

In 2010, a study found that women with type O blood may find it harder to conceive than people with different blood groups. Those with type A blood appeared to be more fertile.

15. Blood can also be dangerous to a baby

During testing, pregnant women are offered blood tests. One of them determines whether they are "rhesus positive" or "rhesus negative." Those who are positive have a certain antigen on the surface of their blood cells, which can mean problems during pregnancy.

If a woman has a baby with a man who is rhesus positive, the child may have rhesus positive blood too, even if she is rhesus negative. In this instance, the woman can develop antibodies against the rhesus antigens. This usually isn't a problem in the first pregnancy, but may cause issues for subsequent ones.

16. Pregnancy brain might be a real thing

Around 80% of women have memory impairment, according to research. But it's unclear what could be causing it. It might be the late nights, exhaustion, and the stress of welcoming a new life into the world.

17. Babies can taste certain foods in the womb

Strong flavours such as garlic can pass through amniotic fluid, so the baby can "taste" them. In fact, when pregnant mothers drank a lot of carrot juice for a study, their babies were more likely to develop a taste for it.

18. The most twins in the world are born in Central Africa

Benin in Central Africa has the highest national number of twins on average, at 27.9 per 1,000 births.

19. Pregnant women can start to lactate when they hear a baby crying

It doesn't have to be their own baby. It's all automatic.

20. Heartburn really could mean a baby with more hair

A small study found there could be some truth to the old wive's tale. Higher levels of oestrogen and progesterone can stimulate hair growth and also relax oesophagus, resulting in acid reflux, or heartburn.

21. The most amount of babies born at once is eight

Six boys and two girls.

22. At age 30 a couple has a 20% change of conceiving

But this decreases to 5% by age 40.

23. Pregnant women produce more oestrogen in a day than non-pregnant women do in a year

Women grow a placenta — an extra organ — during pregnancy, which produces hormones. At full term, a pregnant woman will produce more oestrogen in a day than a non-pregnant woman will in three years.

24. Babies can cry in the womb

Researchers discovered this by accident when studying pregnant women who smoked or used cocaine. When a sound was played on the pregnant bellies, babies could be seen on an ultrasound startling when hearing it and opening their mouths.

25. Mothers may get gingivitis and bad breath

The hormonal changes of pregnancy can make women's gums more susceptible to plaque, which can lead to inflammation and bleeding — called pregnancy gingivitis.

26. There could be a reason for strange cravings

Hormonal changes may disrupt pregnant women's taste and smell receptors, leading to them crave strange foods. Cravings could also be a sign that mother and baby are lacking in certain nutrients. For instance, craving red meat could indicate a deficiency of iron.

27. Your partner may experience some of the same symptoms

It's called couvade syndrome — or sympathetic pregnancy. According to the Mayo Clinic, more research is needed to determine whether it has psychological causes, but men have reported symptoms like nausea, heartburn, abdominal pain, back ache, anxiety, and depression.

28. Pregnant women often get thicker, shinier hair — but they also get more body hair

During pregnancy, hair can feel fuller and healthier, because it can grow faster. But women may also grow hair on other parts of their body, such as their abdomen, face, and back.

29. Fetal stem cells can travel around the body, repairing things

A few years ago researchers discovered fetal cells in mothers' brains. As it turns out, fetal cells can migrate from the placenta into the mother's organs, which can help repair damaged tissues. The cells can also spark immune disorders.

30. During birth, the pelvic bone separates

The pelvis is connected by a narrow section of cartilage and ligament, which can sometimes separate during childbirth. For some, it may never fully fuse back together again.

31. Being pregnant can cause carpal tunnel syndrome

Pregnant women can experience swelling in their hands due to a build up of fluid in tissues. Sometimes, this fluid can collect in the carpal tunnel, causing pressure on nerves, leading to tingling and numbness in hands and fingers. According to the NHS, as much as 60% of pregnant women may experience these symptoms.

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