10 bizarre facts about newborns you won't read in your Facebook mum's group.

These days we are inundated with information about our babies before we even give birth. From 3D ultrasounds to Facebook mother’s groups, we know every tiny detail – and sometimes way too many facts.

But there are a few you may not know. A few that might surprise you just as much as they surprised me.

1. Newborns get all hairy in the womb then eat their own hair.

Yep. Those cute fuzzy little heads of hair you ruffle and snuggle with delight when they are born once stretched right across your baby's entire body, like a teeny-tiny baby ape.

Dr Stephen Juan has written that when a fetus is about four months into pregnancy it develops a mustache that, over the course of a month, spreads over its entire body. The unborn baby remains completely hairy for many weeks.

Don't worry its a soft, downy coat called lanugo and is usually shed before birth.

But did you know how? Well your baby swallows it  - each of the tiny hairs and then expelled in their first poo.

2. Babies don't have bony kneecaps.

While they do have kneecaps it’s just a structure of cartilage that eventually forms into a kneecap as we know it. We are told that this lack of proper kneecaps is nature’s way of helping babies crawl as the cartilage absorbs the hard surfaces they encounter.

3. Your baby’s eyes are 75% their adult size at birth.

Those large doe-like eyes gazing at you isn’t just unique to your newborn, in fact baby eyeballs are gigantic compared to their heads, already 75% their adult size. Your newborn is also near-sighted. Upon birth they are 20/400 but by the time they're six months old the majority can see 20/20.

4. Baby boys get erections while in the womb.

We might just leave that fact there for you to ponder.

5. And while you are on that – baby girls can menstruate.

When babies are in the womb, they absorb hormones from their mothers. That means that female babies shed their uterine lining and can have a mini period. It’s called pseudomenstruation and is similar to menstruation in young and adult women.

6. Mothers will retain some of their baby’s cells.

This is kind of beautiful in a science way. The process, called fetal-maternal microchimerism describes the way that fetal cells are retained in a mother after birth. Science News reports that fetal cells can be woven into a mother’s brain, her blood, liver, lungs and even hearts.

Think giving birth is the hard bit? Wait till you have to work out how to breastfeeding in public. Post continues after video..

7. Your baby can’t taste salt.

According to Parenting Science while newborns can taste sweetness, saltiness, bitterness, sourness and umami from birth the one they can’t taste is salt.

Experiments suggest that babies can’t taste salt until they are about 4 months old.

So save those salt and vinegar chips for yourself....

8. Newborns don't actually cry tears.

It isn't until at least the third week of their life that they start to produce tears when they're crying.

But don’t worry when they cry there is no doubt you will hear it.

9. Your baby has drunk their own pee.

Delicious little creatures aren’t they, all squishy and innocent and filled to the brim with their own pee they drank while in your womb.

The little mites start urinating in the womb just a few months after conception and as it mixes with amniotic fluid they drink it.

Tasty.

10. Your baby can remember tastes from when they were in utero.

Speaking of tastes, did you have a penchant for spicy foods when you were pregnant?

Garlic?

Or the sweet stuff? Turns out that your child probably will too when they start on solid foods.

From around 21 weeks babies can taste the foods you eat through the amniotic fluid they intake ( thats the same stuff they are pee-ing into and drinking.)

Julie Mennella has written for Pediatrics that there isn't a single flavor they have found that doesn't show up in utero.

"Things like vanilla, carrot, garlic, anise, mint — these are some of the flavors that have been shown to be transmitted to amniotic fluid or mother's milk,” she said.

Your baby is a truly fascinating, amazing little unique creature.

Enjoy each and very moment - and those salt and vinegar chips.

What fun facts surprised you during your pregnancy?