12 Weeks Pregnant – What to Expect Your 12th Week of Pregnancy

by Claire October 15, 2015, 4:12 am 2k Views 28 Comments

Pregnancy author Heidi Murkoff from the best selling What To Expect series tells us what’s happening at 12 weeks of pregnancy.

While it’s hard to believe, your baby has more than doubled in size the past three weeks! He or she is now the size of a plum and has a functioning digestive system.

It’s a landmark week for your little one, since most of his key body systems and vital organs are fully formed by now. Your baby will spend the rest of his gestation bringing those systems up to speed and full maturation so they’ll be able to function to perfection once his big birthday arrives.

Your fetus can now boast the achievement of having more than doubled in size in just three weeks. Crown-to-rump length is about two and a half inches, so he’s about the size of a kiwi, but weighs a lot less, just half an ounce. A fair amount of heft is in that crown: basic brain structure is complete and now it’s time for that brain mass to rapidly increase.

Your baby’s thyroid is now fully formed, the pituitary gland has started producing hormones, and the pancreas has begun to synthesize insulin. Not to be outdone, your baby’s bone marrow is churning out white blood cells, the critical weapons needed to fight infection once your little warrior is on the outside and no longer protected by your immune system.

Muscles in the digestive tract are getting primed, practicing their contractions so they can process food – and lots and lots of poop – after birth. And even though much of the small intestines are still folded up in storage in the umbilical cord, the villi – tiny, finger-like projections that absorb nutrients from food – are now in place.

The best development of all? If you haven’t already heard it, this is the week that your cutie’s heartbeat will come through loud and clear at your checkup. And that’ll be music to your ears.

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Written by Claire

Claire is our Community Manager here at New Moms Forum. A mom of two (almost grown-up babies), Claire has been building and operating community-based websites for almost 20 years. In her downtime, Claire enjoys spending time with her family and drinking copious amounts of red wine!