You are now 12 weeks pregnant and in the final stretch of the first trimester! Your little one has come such a long way already, and your body continues to do amazing things. Let’s take a look inside week 12 of your pregnancy!
Estimated reading time: 7 minutes
Table of contents
Week 12 Pregnancy: Baby’s Development
You’re twelve weeks pregnant, and in just 10 weeks since your baby was conceived, pretty much all structures have formed! They will still need a lot of time to grow and develop, though. At around 2 1/2 inches crown-to-rump, baby is about the size of a plum… though he or she weighs considerably less at just 1/2 ounce. (1) Still, it’s amazing that this tiny one is twice the size it was in week 9, just three weeks ago! This week:
- Baby’s heartbeat can probably be heard with a doppler, a special listening machine that magnifies the sound
- Baby has a cute little face with eyes that have moved to the front and ears that are just where they should be
- Hair begins to appear on baby’s body
- The small intestine can push food through the bowels and absorb sugar
Week 12 Pregnancy: Pregnant Belly
Your bump likely looks similar to last week and is still a cute, tiny thing. We’ve talked a lot about baby’s development, and about what your bump might look like from the outside. This week, let’s take a closer look at what’s going on inside your uterus in week 12 pregnancy.
Before pregnancy, your uterus holds 10 ml (1/3 ounce). By the time you deliver, it will have grown to the size of a watermelon, with its capacity increasing 500 to 1,000 times. It will be able to hold a full-term baby, placenta, and amniotic fluid (and even more in pregnancies of multiples!). Your uterus itself will grow from a pre-pregnancy weight of about 2 1/2 ounces to almost 40 ounces! For right now, your uterus is grapefruit-sized, containing a 2 1/2 inch baby who weighs around half an ounce, a placenta, and about 1 1/2 ounces of amniotic fluid. (1)
By week 12 of pregnancy, the placenta is completely formed. This important, hard-working organ is the lifeline between you and your baby. Not only does it exchange nutrients and waste products between you and baby, it also produces hormones and signaling molecules that are necessary for both of you during pregnancy.
The Placenta as a Delivery System
Your blood and baby’s blood don’t mix during pregnancy. The placenta absorbs nutrients, immune molecules, and oxygen molecules from your blood as is flows through your uterus. It passes these through the umbilical cord to your baby. Waste products pass from your baby through the umbilical cord to the placenta where they can pass into your blood to be eliminated by your kidneys and lungs. (2)
The Placenta as a Security System
In addition to delivering the good things your baby needs to grow and develop, the placenta helps to block things that could harm him. It is pretty good at keeping out bacteria, though not as effective at keeping viruses out. It also keeps baby’s cells from entering your bloodstream where your body could see them as foreign material and reject the baby. As amazing as the placenta is, though, it isn’t able to filter out everything that could possibly harm your baby. This is why it’s vital that you don’t drink alcohol while pregnant, and consult your doctor before taking any medications.
Your baby is surrounded by the amniotic sac, sometimes called the membranes or bag of waters. It is a pair of membranes, the amnion and chorion, that are thin and transparent but tough. The amniotic fluid helps maintain an even temperature, provides for easy movement, and keeps your baby protected by absorbing outside bumps. (2)
Week 12 Pregnancy: Symptoms
A Little Relief
Many pregnant women who suffer from morning sickness find that it is beginning to improve by week 12 pregnancy. The fatigue and exhaustion of the first couple months often improves as well. The wild ride of early hormonal changes has settled down a little bit, and you’re not big enough to be too uncomfortable. The second trimester is the most comfortable part of pregnancy for many women.
Hair and Nails
Many women notice changes, for better or worse, in their hair or nails during pregnancy. Some women see an increase in hair and nail growth, while others find that their hair thins or their nails break more easily. Both of these are normal, and are likely the result of either increased circulation or — you guessed it — hormone changes.
Pregnancy can cause a number of skin changes due to things like the stretching of the skin itself and hormonal effects on things like melanin, which produces pigment in your skin.
Also called “mask of pregnancy,” melasma, also known as cholasma, gives some women brownish marks around their eyes and on their cheeks and noses. This increases with sun exposure, so the best way to prevent it is to avoid sun exposure, use sunscreen, wear hats, etc. The marks usually fade after delivery. (1, 3)
The faint line that runs from belly button to the pubic hair often gets darker during pregnancy. This may fade after pregnancy but is sometimes permanent.
Dry, Itchy Skin
Many pregnant women have dry, itchy skin. Moisturizers can help, but you can also improve it by staying hydrated and eating omega-3 fatty acids. Good sources of omega-3s are fish, olive oil, almonds, and macadamia nuts. (1)
While they usually don’t appear until later, no discussion of skin changes in pregnancy is complete without covering stretch marks. The skin on your belly and breasts (and sometimes even buttocks, thighs, and hips) may develop streaks that are red, purple, or reddish-brown depending on your skin color. Changes in the elastic supportive tissue beneath the skin are responsible for stretch marks, and there are no proven ways to keep them from developing or make them go away once they do. (3)
Check in next week to learn what’s going on in your body and your baby’s in week 13!
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- Glade, B.C., Schuler, J. (2011). Your Pregnancy Week by Week, 7th edition. First Da Capo Press
- Simkin, P. (2010). Pregnancy, Childbirth and the Newborn, 4th edition. Meadowbrook Press
- The American College of Obstetricians and Gynecologists. (2010). Your Pregnancy and Childbirth Month to Month, 5th edition.