This is a big week for your baby: Your little one's key body systems and vital organs are now fully formed! If you haven't already, you'll be able to hear your baby's heartbeat at your next prenatal checkup.
Meanwhile, at 12 weeks pregnant, your baby bump may be looking a little more pronounced.
Your Baby at Week 12
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 birth-day 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 music to your ears.
At a Glance
12 weeks pregnant is how many months?
If you're 12 weeks pregnant, you're in month 3 of your pregnancy. Only 6 months left to go! Still have questions? Here's some more information on how weeks, months and trimesters are broken down in pregnancy.
How big is my baby at 12 weeks?
By now your baby weighs a full half-ounce, with a crown-to-rump length of 2 to 2¼ inches: about the size of a lime.
It's hard to believe — especially from the outside, since you're probably barely showing at this point — but your baby has more than doubled in size during the past three weeks.
Baby’s digestive system begins working
This week marks a turning point for your baby. At 12 weeks pregnant, the Herculean task of developing new bodily structures is nearing an end, as most of your baby's systems are fully formed — though there's still plenty of maturing to do.
Now comes the maintenance phase, during which your fetus' systems continue to evolve for the next 28 weeks and the organs get to work. For one thing, the fetal digestive system is beginning to flex its muscles — literally — as it starts practicing contraction movements, a skill your little peanut will need after birth to push food through the digestive tract.
The bone marrow is busy making white blood cells — weapons that will one day help your baby fight infection once she's out of your safe haven and in a regular play group. And the pituitary gland at the base of the brain has started producing the hormones that'll enable her to make babies of her own in a few decades or so.
If you haven't already had the pleasure, it's likely that at this month's checkup you'll finally hear your baby's fetal heartbeat — a sound that will make your heart race with joy!
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