Your baby this week
Your baby's one-of-a-kind fingerprints are forming, and the nails keep growing. Behind closed lids, the eyes move, the mouth opens and closes, and a loud noise can make your baby startle.
At 17 weeks the first fat starts to build up under your baby's skin, which will help with temperature control later. The umbilical cord is growing thicker and stronger. Hearing is developing quickly, and outside sounds reach your baby in muffled form. For you, a growing uterus often causes round ligament pain: a brief, sharp twinge low on one or both sides, especially when you move suddenly, cough or sneeze. Slower movements and rest usually help. Pain that's severe or lasting, or that comes with bleeding or a fever, needs a call to your provider. If your anatomy scan isn't booked yet, schedule it now, since many practices fill up weeks ahead.
By the numbers
Week 17 covers days 119 to 125 counted from the first day of your last period, which is 43% of a 40-week pregnancy. About 161 days remain until a 40-week due date. Since last week, an average baby gains about 1.2 oz (35 g). By date of conception, your baby is about 15 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
As your belly grows, you may feel brief, sharp twinges low on the sides as the ligaments that support your uterus stretch. Call your provider if the pain is severe or doesn't ease with rest.
Tests and to-dos this week
Book your anatomy ultrasound for 18 to 22 weeks if it isn't scheduled yet. Comfortable maternity clothes and a supportive bra can make a big difference.
Quad screen (optional) · weeks 15–22 · test
Coming up: Anatomy ultrasound (from week 18). Full prenatal visit schedule
Tips for the second trimester
- Most healthy pregnant people are advised to get about 150 minutes of moderate activity a week, such as walking or swimming.
- Your recommended weight gain depends on your pre-pregnancy BMI, and gain usually speeds up in the second trimester.
- Once you feel your baby regularly, learn their usual pattern; a change in pattern matters more than any count.
- The flu shot is recommended at any point in pregnancy during flu season.
Call your provider or labor and delivery right away if you have:
- vaginal bleeding or leaking fluid
- regular contractions or pelvic pressure before 37 weeks
- a severe headache, vision changes, or sudden swelling of the face or hands
- a fever of 100.4 °F (38 °C) or higher, or painful urination
- after 24 weeks, your baby moving less or differently
In an emergency, call 911.
Last week and next week
Last week (16): Your baby can now make fleeting facial expressions and curl the hands into fists.
Frequently asked questions
How big is the baby at 17 weeks?
About the size of a pomegranate: about 4.7 in (12 cm) · 6.3 oz (179 g), measured crown to rump. These are rounded averages, and every baby grows at their own pace.
How many months is 17 weeks pregnant?
17 weeks is in month 4 and the second trimester. About 23 weeks (161 days) remain until a 40-week due date. Months are approximate; providers count weeks and days.
What is the sharp pain on the side of my belly at 17 weeks?
Most often it's round ligament pain from the ligaments supporting your uterus stretching; it's brief and triggered by movement. Call your provider if it's severe or lasting, or comes with bleeding, fever or painful urination.
What's the next test or appointment after week 17?
Next up: Anatomy ultrasound, from week 18. 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