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Lots of things go crazy in a woman's body when she's pregnant, but Hank tells you about three cool phenomena you might not have heard about. You'll want to thank your mom when you find out what they are!

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Hank Green: Your consciousness has been hanging around inside of a human body for a while, so you'd know that it's capable of some really amazing, weird, and often unexpected stuff, whether you want to control that stuff or not.  But there few things that corpus humanus goes through that are weirder and more amazing than when a female body is making another body inside of it.

Pregnancy is enormously taxing on a body, of course, because it's basically making all kinds of arrangements to accommodate another separate body within it, in addition to being incredibly uncomfortable and demanding, it also creates crazy carnival of hormones, those chemical signals that tell your organ systems what to do and when, all of which have distinct purposes to help nurture the baby and prepare for its arrival.  A whole alphabet soup of these chemicals spill out from glands all over a woman's body with names like LH, FSH, and HGC, and many of them are just triggers to release more hormones that you probably have heard of, like estrogen and progesterone, but some of these effects of these hormones are more useful than others.  

For example, most women, especially when they first become pregnant, experience a heightened sense of smell.  This change can be so sudden and acute that it's often used to diagnose an early pregnancy.  But rather than making women able to better detect smells, a rare condition known as hyperosmia, they instead just make women extremely sensitive to smells of all kinds.  Food, perfume, smoke, happy bunny farts, old fashioned B.O, all seem equally intense and usually unpleasant.  No one is sure what, if any, purpose this heightened olfactory activity might serve, but some scientists think it's the real root of morning sickness, the queasiness and vomiting that often accompanies the first trimester of pregnancy.  This hypothesis has been supported by the fact that pregnant women who have no sense of smell, a condition known as anosmia, have been found to not get morning sickness at all.  

Another odd and arguably even less useful symptom of pregnancy is physically visible even before the baby bump starts to show: in many women, a dark stripe appears right down the middle of their bodies, from the belly button to the genitals.  Doctors call it linea nigra, and it, too, has been linked to maxed out levels of estrogen and other hormones.  In some cases, women's skin can get darker everywhere, with freckles and moles appearing, even in women who already have dark skin.  And some develop chloasma, a darkening of facial skin, especially around the eyes.  That's something known as the mask of pregnancy.  I guess this is nature's way of saying 'congratulations on having a person inside you, in addition to being bloated and constipated, you also look a little bit like a raccoon!  

And it is tempting to think that there's some evolutionary point to these discolorations, like, just making it abundantly obvious to others when a female is pregnant, but again, scientists are stumped about why this happens.  

But at least some good can come from having a totally out of control body--you can have a clean house.  Though it's long been part of the folklore surrounding pregnancy, scientists have recently verified that many pregnant women go through a bout of nesting.  Not long before a baby arrives, women often exhibit an uncontrollable urge to clean and organize their homes: sorting dishes in the kitchen, folding and sorting the baby's clothes, while they also become more sensitive about who they let in their home and who they spend time with.  A study at McMaster University in 2013 compared the behavior of pregnant and non-pregnant women over the same extended period.  They found that sometime in the last trimester, pregnant women consistently exhibited these same behavior patterns, while the non-pregnant ones just walked around like normal people.  And even though it might seem kind of weird or neurotic, scientists say that this nesting instinct is an ancient adaptation which eases the transition for both mother and offspring, and promotes bonding even before the mother and child meet.  

So thank you, for all of the mothers out there, for going through all that weird stuff, and especially thanks to my mom.  And also thanks to you for watching this episode of SciShow.  If you have any questions, comments, or ideas for us, we're down at the comments below, and on Facebook and Twitter, and if you want to keep getting smarter with us here at SciShow, you can go to and subscribe.  

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