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13 Weeks Pregnant: The Second Trimester Begins & Your Baby's Bones Start to Harden

Medically reviewed by

Verena Brehm, Midwife Jul 29, 2026

Line illustration of a plum: at 13 weeks pregnant your baby is about the size of a plum, roughly 6.4 to 7.6cm

Line drawing of a 13-week foetus with the head growing more proportionate to the body and longer, slimmer limbs

Line drawing of a woman's torso at 13 weeks pregnant, showing the uterus rising toward the navel with the first gentle curve of a bump

Your baby is the size of a

Plum

Small and climbing — ~45 g (1½ oz) by week 14

~6.4–7.6 cm / ~2.5–3 in

Key Takeaways

At 13 weeks pregnant, you're crossing into the second trimester. The SOGC notes the nausea and vomiting of early pregnancy usually "eases up by the 12th week" — so for many women, this is where queasiness lifts and some energy returns.

Your baby is roughly the size of a plum — about 2.5 to 3 inches (6.4 to 7.6 cm) at the close of the first trimester, per Cleveland Clinic. Vocal cords are forming and bones are starting to harden, especially in the skull and limbs, per Mayo Clinic.

The risk of miscarriage "drops considerably after 12 weeks," according to Cleveland Clinic. Keep taking 400 mcg of folic acid daily, and hold caffeine to no more than 300 mg a day — the maximum Health Canada recommends during pregnancy.

Your Baby at 13 Weeks: Development & Growth

At 13 weeks pregnant, your baby is roughly plum-sized — about 2.5 to 3 inches (6.4 to 7.6 cm) at the close of the first trimester, according to Cleveland Clinic. Bones are beginning to harden in the skeleton, "especially in the skull and long bones of the arms and legs," according to the Mayo Clinic.

Your baby is small but no longer abstract. Cleveland Clinic describes the fetus at the end of the first trimester as "about 2.5 to 3 inches long — about the size of a plum," which is roughly 6.4 to 7.6 cm. By week 14, the Mayo Clinic puts it at about 8.7 cm (3½ inches) crown to rump, weighing about 45 g (1½ ounces). Your 13-week baby sits between those two points.

The skeleton is stiffening. The Mayo Clinic notes that at "thirteen weeks into pregnancy, or 11 weeks after conception, bones start to harden in your baby's skeleton, especially in the skull and long bones of the arms and legs." The same source adds that the skin is still "thin and transparent" — but that soon it will start to get thicker.

Proportions are catching up, too. Cleveland Clinic notes that around week 13 the "vocal cords form and the fetus's large head begins to grow proportionate to its body." That oversized head, so striking on earlier scans, is slowly becoming the head of a baby rather than the head of an embryo.

Most of the hard construction is behind you now. Cleveland Clinic notes that by the end of week 12 all the organs, limbs, bones and muscles are present and "will continue to develop in order to become fully functional." From here, the work is mostly growing and refining what's already there — which is exactly why this stage feels like a turning point.

Your Body at 13 Weeks: Symptoms & Changes

At 13 weeks pregnant, many women find early nausea easing — Pregnancy Info, from the Society of Obstetricians and Gynaecologists of Canada, notes it "eases up by the 12th week." Common symptoms across pregnancy include fatigue, tender breasts, frequent urination, constipation and mood swings. Any vaginal bleeding should be checked — contact your health care provider as soon as you notice it.

The most welcome change is often the one you stop noticing. Pregnancy Info, from the Society of Obstetricians and Gynaecologists of Canada, notes that nausea and vomiting "usually starts around the sixth week of pregnancy and eases up by the 12th week." For some women it lingers longer, and that happens — but week 13 is frequently where the worst of it starts to loosen its grip.

Some symptoms carry on regardless. Pregnancy Info lists fatigue, tender or swollen breasts, frequent urination, constipation, bloating, backaches, headaches and mood swings among the common symptoms of pregnancy. Some of these ease as the trimester goes on. Others come and go. As the same source puts it, "every pregnant woman is different" — some "sail through pregnancy with very few symptoms," while others are "dogged with multiple discomforts."

One thing to take seriously at any stage: bleeding. Pregnancy Info advises that "it's important for you to take any vaginal bleeding seriously" and to "contact your health care provider as soon as you notice any bleeding." It notes that about one-third of pregnancies have some bleeding before the 20th week, and about half of these continue without further issues — but it should always be assessed, not waited out.

You may be starting to show, or you may not be. Cleveland Clinic notes that many people "begin showing signs of being pregnant at this point in pregnancy, especially if you've been pregnant before." If your body hasn't changed visibly yet, that's within the normal range too.

What to Do at 13 Weeks Pregnant

NUTRITION AT 13 WEEKS PREGNANT

Eat a varied, nutrient-dense diet. Pregnancy Info, from the Society of Obstetricians and Gynaecologists of Canada, recommends "a varied, nutrient-dense diet, as recommended by Canada’s Food Guide," and notes that eating well "doesn’t always mean eating more, but it does mean being conscious of the quality of your diet."
Don’t rush to eat much more just yet. Pregnancy Info notes that "during the first trimester, you likely don’t need any extra calories," and that "in the second trimester you need about 340 extra calories per day" — roughly 2 or 3 extra servings from Canada’s Food Guide, not a free-for-all.
Keep caffeine to no more than 300 mg a day. Health Canada recommends a maximum daily caffeine intake of 300 mg for people who are pregnant — about two 8 oz (237 ml) cups of brewed coffee, which it lists at roughly 135 mg each.
Include folate-rich foods and foods fortified with folic acid. Note that folate-rich foods don’t replace supplements. The Public Health Agency of Canada lists corn, oranges, beans, lentils and dark green vegetables like peas, spinach, broccoli and brussels sprouts as sources of folate — while stressing that "dietary sources on their own are not enough" to protect against neural tube defects.

WHAT SUPPLEMENTS TO TAKE AT 13 WEEKS PREGNANT

Keep taking 400 mcg of folic acid every day. The Public Health Agency of Canada recommends "a daily multivitamin with 400 mcg (0.4 mg) of folic acid" for anyone who could become pregnant, continued "throughout your pregnancy and while breastfeeding." It also warns: do not increase your dose "beyond 1 mg per day without talking to your health care provider."
Ask your provider about iron. Pregnancy Info notes that iron needs rise to 27 mg daily "during the final six+ months of pregnancy," and that iron "is safe to stop supplementing" during the first trimester if you’re dealing with nausea. Now is a sensible time to check where you stand.
Take supplements only as directed on the label.

LIFESTYLE TIPS AT 13 WEEKS PREGNANT

Use returning energy to move. Pregnancy Info advises that "all pregnant women should be physically active throughout pregnancy" and should "accumulate at least 150 minutes of moderate intensity physical activity each week" — walking, swimming and stationary cycling are all good options. Reduce your activity if you’re experiencing physical discomfort.
Ask about first-trimester screening. If the first-trimester ultrasound has not yet been performed, this can still be done. Pregnancy Info notes that "all women should be offered prenatal genetic screening," and that tests like nuchal translucency and chorionic villus sampling (usually done "between 10 and 13 weeks") fall in this window. Whether to have them is your choice.
Check any medicine before you take it. Pregnancy Info advises talking to your health care provider before taking prescriptions, over-the-counter drugs or natural and herbal products.

When to Contact Your Doctor or Midwife

Contact your doctor, midwife or other health care provider if you experience:

Any vaginal bleeding — even if it is light. Pregnancy Info, from the Society of Obstetricians and Gynaecologists of Canada, advises taking any bleeding seriously and contacting your health care provider as soon as you notice it.
Signs of infection, such as fever — Pregnancy Info advises you should see your care provider right away if you have these signs.
Severe or persistent vomiting — vomiting so severe that you're missing meals, struggling to get through normal activities, or losing weight. Pregnancy Info notes this is not normal and that other treatments can help, so see your health care provider.
Cramping, pain, or passing clots — passage of clots or tissue, or cramping and pain in the lower pelvis or back. Pregnancy Info lists these among the signs of a pregnancy loss; contact your provider for guidance.
Severe pain or feeling faint — severe abdominal pain, heavy bleeding, or feeling faint. Seek emergency medical care immediately.
Any concern that's worrying you — your health care provider is there for exactly this.

Frequently Asked Questions

How big is my baby at 13 weeks pregnant?

At 13 weeks pregnant, your baby is roughly plum-sized. Cleveland Clinic puts the fetus at "about 2.5 to 3 inches long" — around 6.4 to 7.6 cm, crown to rump — at the close of the first trimester, and the Mayo Clinic puts it at about 8.7 cm (3½ inches) and 45 g (1½ ounces) by week 14. Your 13-week baby sits between those two figures. Bones are just beginning to harden in the skull and the long bones of the arms and legs, according to the Mayo Clinic.

Is it normal to still feel nauseous at 13 weeks pregnant?

Yes. While Pregnancy Info, from the Society of Obstetricians and Gynaecologists of Canada, notes that nausea and vomiting usually "eases up by the 12th week," it also says that "for some women it persists throughout pregnancy." What is not normal, per the same source, is nausea and vomiting so severe that you’re missing meals, struggling with normal activities, or losing weight — see your health care provider, as other treatments can help.

Does the miscarriage risk drop at 13 weeks?

The risk becomes lower once you’re past the first trimester. Cleveland Clinic notes that your chance of miscarriage "drops considerably after 12 weeks (the end of the first trimester)," once the most critical development has taken place. Pregnancy Info notes that pregnancy losses are most common in the first 8 weeks. If you have any vaginal bleeding, contact your health care provider as soon as you notice it.

How much caffeine can I have at 13 weeks pregnant?

Health Canada recommends a maximum of 300 mg of caffeine a day for people who are pregnant. That’s roughly two 8 oz (237 ml) cups of brewed coffee, which Health Canada lists at about 135 mg of caffeine each. Remember that tea, cola and chocolate contain caffeine too, so they count toward your daily total.

What tests happen around 13 weeks pregnant?

This is a common window for first-trimester screening. Pregnancy Info notes that "all women should be offered prenatal genetic screening," which can include a blood test and a nuchal translucency ultrasound that measures fluid at the back of the baby’s neck. Chorionic villus sampling, when it’s used, is "usually" done "between 10 and 13 weeks." These are screening tests and your choice.

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Sources & References

Public Health Agency of Canada — Folic acid, healthy pregnancy and neural tube defect prevention
Health Canada — Caffeine in Foods
Pregnancy Info (SOGC) — Nausea and vomiting
Pregnancy Info (SOGC) — Symptoms of pregnancy
Pregnancy Info (SOGC) — Healthy eating
Pregnancy Info (SOGC) — Exercise during pregnancy
Pregnancy Info (SOGC) — Prenatal genetic screening
Pregnancy Info (SOGC) — Pregnancy Loss
Mayo Clinic — Fetal development: The 2nd trimester
Cleveland Clinic — Fetal Development: Week-by-Week Stages of Pregnancy

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