Your baby this week
Ovaries or testes have developed. Movements are becoming more purposeful, and your baby may even suck a thumb. You probably won't feel any of it for a few more weeks.
Week 13 is the last week of the first trimester. Your baby's intestines, which partly developed inside the umbilical cord, are moving back into the abdomen. Vocal cords are forming, and the bones are strengthening quickly. The placenta has fully taken over nourishment and hormone production. You may notice more white, milky discharge, which is normal. Itching, a strong smell or a green or gray color can signal an infection, so tell your provider; it's very treatable in pregnancy. If you haven't seen a dentist recently, now's a good time: gums are more sensitive in pregnancy, and routine dental care, cleanings and X-rays with shielding are considered safe.
By the numbers
Week 13 covers days 91 to 97 counted from the first day of your last period, which is 33% of a 40-week pregnancy. About 189 days remain until a 40-week due date. Since last week, an average baby gains about 0.5 oz (15 g). By date of conception, your baby is about 11 weeks old.
Pregnancy is dated from the first day of your last period, so conception happens around week 2. Your due date is 280 days (40 weeks) from that day, and an early ultrasound may adjust it.
Your body
You may notice more white, milky discharge, which is normal. Call your provider if it smells bad, turns green or itches.
Tests and to-dos this week
As the first trimester ends, make sure your initial blood work and any screening you chose are done. Checkups are typically monthly until 28 weeks.
First-trimester labs · weeks 6–13 · test
Blood type and Rh factor, antibody screen, blood count, and infection screening including syphilis (ACOG recommends syphilis testing at the first visit, in the third trimester and at delivery).
First-trimester screening (blood test + NT ultrasound) · weeks 10–13 · test
Optional genetic screening, usually done together between 10 and 13 weeks.
Coming up: Quad screen (optional) (from week 15). Full prenatal visit schedule
Tips for the first trimester
- Take 400 micrograms of folic acid a day; your provider may advise a higher dose if neural tube defects run in your family.
- Avoid alcohol, smoking, raw or undercooked meat, fish and eggs, and unpasteurized dairy.
- For nausea, try small, frequent meals and sipping fluids; call your provider if you can't keep anything down.
- Check every medicine and supplement you take with your provider or pharmacist before continuing.
Call your provider or labor and delivery right away if you have:
- severe or worsening belly pain, especially on one side or spreading to your shoulder
- heavy bleeding or passing clots
- feeling faint, dizzy or very pale
- a fever of 100.4 °F (38 °C) or higher
- vomiting so severe you can't keep fluids down
In an emergency, call 911.
Last week and next week
Last week (12): Your baby's organs and muscles are in place and now mainly need to grow and mature.
Next week (14): Your baby's head is coming into better proportion with the body.
Frequently asked questions
How big is the baby at 13 weeks?
About the size of a lemon: about 2.7 in (6.8 cm) · 2.6 oz (73 g), measured crown to rump. These are rounded averages, and every baby grows at their own pace.
How many months is 13 weeks pregnant?
13 weeks is in month 3 and the first trimester. About 27 weeks (189 days) remain until a 40-week due date. Months are approximate; providers count weeks and days.
When does the second trimester start?
At 14 weeks 0 days. The first trimester runs through 13 weeks 6 days, the second through 27 weeks 6 days, and the third until birth.
What's the next test or appointment after week 13?
Next up: Quad screen (optional), from week 15. Your provider may schedule things differently depending on your health and local practice.
Sources
- WHO Fetal Growth Charts (Kiserud et al., PLoS Med 2017)
- INTERGROWTH-21st crown-rump length standard (Papageorghiou et al., 2014)
- Hadlock et al.: In utero fetal weight standard (Radiology 1991)
- NHS: Week-by-week guide to pregnancy
- NHS: Pregnancy symptoms you need to get help for
- ACOG: How Your Fetus Grows During Pregnancy
- ACOG: Routine Tests During Pregnancy
- ACOG: Prenatal Genetic Screening Tests
- CDC: Vaccine Recommendations Before, During, and After Pregnancy
- Office on Women's Health: Prenatal care and tests
- Hungarian Decree 26/2014 (IV. 8.) EMMI on prenatal care
- NNGYK (Hungary): 2026 vaccination methodology letter
- ACOG – Group B Strep and Pregnancy (Committee Opinion 797)
- ACOG – The Rh Factor
Last reviewed: November 14, 2026 · Kitpebble editorial team
This page is for general information. It isn't medical advice or a diagnosis and doesn't replace your OB-GYN or midwife. Sizes are rounded averages. Our editorial policy