13 Weeks Pregnant: Your Baby’s Development

This week, your little one’s organs are fully formed and are hard at work! The kidneys are starting to produce urine and release it into the amniotic fluid, and the spleen is busy producing red blood cells, which carry oxygen throughout the body.

Your baby's intestines have moved back into the abdomen from the umbilical cord, now that there’s enough room to accommodate them, and some of the larger bones, including those of the skull, are beginning to harden.

What else is happening with your baby? Even though you won’t hear those tiny coos and cries until after you give birth, your baby’s little vocal cords have already started to develop.

If you’re 13 weeks pregnant with twins, read more about your babies’ development in our weekly twin pregnancy overview.

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How Big Is Your Baby at 13 Weeks?

Your fetus is about the size of a large plum or a small peach.

Mom’s Body at 13 Weeks Pregnant

You’ve just about made it to your second trimester, which many moms-to-be describe as the honeymoon period of pregnancy. The discomforts you may have experienced in the first trimester — fatigue, nausea, and frequent urination — often ease up a bit, and you may even feel a surge of energy during this trimester.

By this stage, your blood supply and flow are fully linked to the placenta, which will continue to grow as your pregnancy progresses. By the time you give birth, the placenta may weigh about one and a half pounds.

At your upcoming prenatal appointments, your healthcare provider may monitor your fundal height -- the distance from your pubic bone to the top of your uterus (the fundus). This measurement helps your provider determine how your baby is doing by measuring the size of your growing uterus.

Breast tenderness may continue on and off, and other issues like constipation, bloating, and heartburn are normal at this stage, too, as your increased hormone levels can slow down digestion. Learn more about prenatal health, fitness, nutrition, and more in our downloadable pregnancy guide.

13 Weeks Pregnant: Your Symptoms

  • Vaginal discharge. A clear to milky-colored discharge known as leukorrhea may increase around this point in your pregnancy. You might be surprised to learn that this discharge has a unique purpose: It helps keep your vagina and birth canal clear of infection and irritation. If it gets a little messy, panty liners can be a big help.

  • Changing sex drive. It's perfectly normal for you and your partner to feel an increase or a decrease in sexual desire at various times during pregnancy. If your pregnancy is normal and both of you feel the urge, go ahead and enjoy the intimacy. Don't worry — your baby will be safe! Your uterus and the amniotic sac provide protection for your baby. Talk to your healthcare provider if you’re worried or have questions about this or anything else. Note that your provider might advise you to abstain from sex if you have complications including a history of miscarriage or if you are at risk of preterm labor.

  • Heartburn. Heartburn and indigestion can come and go throughout your pregnancy as your baby moves from one position to the next, and as your growing uterus puts pressure on your stomach. Pregnancy hormones also cause the muscle at the top of your stomach to relax, allowing stomach acid to travel up into the esophagus, which causes heartburn; this is more likely to happen if you lie down after having just eaten a large meal. You can reduce the discomfort by sitting upright after eating and avoiding potential triggers such as chocolate, citrus fruits, and fried or spicy foods.

  • Constipation. Hormones strike again! Progesterone and estrogen play an important role in pregnancy, but right now they might be causing your digestive system to work more slowly than usual. This means that you may be feeling a bit backed up. Adding more fruits, vegetables, and whole-grain foods to your diet increases your fiber intake and helps keep things moving along. Drinking prune juice might also help, as can drinking lots of water and doing regular exercise.

  • Leaking colostrum. You may start to notice a thick, yellow fluid leaking from your breasts right about now. This is called colostrum, and it’s the milk that appears for the first few days after you give birth. It is completely normal, but you may want to try using disposable or cotton breast pads (without plastic liners) to help absorb any leaking fluid.

Can’t wait to know whether your little one is a boy or a girl? Try our fun Chinese gender predictor* tool!


13 Weeks Pregnant: Things to Consider

  • Have you shared the good news with your family and friends? The beginning of your second trimester is a great time to do this, because the risk of miscarriage is lower after the first three months. Of course, the decision about when to start spreading the word is totally up to you! Get inspired with our creative pregnancy announcement ideas.

  • If you work, plan when you'll let your boss know that you’re expecting. Start to think about how you will share the news, and when. You’ll want to keep your employer and colleagues in the loop so they can make plans for accommodating your absence during your maternity leave.

  • Working out? If yes, keep it up! If not, consider talking to your healthcare provider about starting a basic fitness routine. If your provider gives you the all-clear, it could include things like walking, swimming, and maybe yoga. Your muscles will thank you – both during the last six months of your pregnancy, and during your new baby’s first few months, when increased fitness will help you deal with all the extra stress that’s placed on your body.

  • If you are doing abdominal exercises that have you lying flat on your back, you may want to look for alternatives during pregnancy, since the weight from your uterus can cause less blood to return to your heart when you're in that position. Ask your healthcare provider for alternatives.

13 Weeks Pregnant: Ask Your Doctor

  • Why do I sometimes feel pain in my pelvic area? (Some pelvic pain may be associated with round ligament pain resulting from things like your growing uterus, but ask your healthcare provider about what’s normal and what isn’t.)

  • Am I gaining the right amount of weight? If not, what changes can I make to get on the right track?

How we wrote this article The information in this article is based on the expert advice found in trusted medical and government sources, such as the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists. You can find a full list of sources used for this article below. The content on this page should not replace professional medical advice. Always consult medical professionals for full diagnosis and treatment.