Second trimester, week 17
17 weeks pregnant: Unique fingerprints
- Size of a
- Pear
- Length
- 13 cm crown to rump
- Weight
- 140 g approximate
- Heart rate
- 110–160 bpm typical range
- Due date
- 161 days away 43% of the way
At 17 weeks pregnant, your baby is about the size of a pear: roughly 13 cm from crown to rump, weighing about 140 g. You’re in your second trimester, with about 23 weeks to go until your due date.
Your baby this week
- The ridge pattern of the fingerprints is being set around now. It is unique, even between identical twins.
- The skeleton is changing from soft cartilage to bone.
- Fat is starting to build under the skin, including brown fat, which helps with warmth after birth.
Your body this week
- Your centre of gravity is shifting. Low, supportive shoes help.
- Appetite often increases. US guidance suggests roughly 340 extra calories a day in the second trimester.
- Stretch marks may appear on the belly, breasts or hips. Genetics matter more than creams.
- Typical weight gain so far
- 2.1–4.1 kg
- Your uterus
- Between pubic bone and belly button
Weight gain range is for a pre-pregnancy BMI of 18.5–24.9 (IOM guideline). Your provider may advise differently.
Scans, tests and checkups
-
This weekSecond-trimester (quad) screening Blood test
A blood test (AFP, hCG, estriol, inhibin-A) for chromosomal conditions and neural tube defects, if you didn’t have first-trimester screening or NIPT. The NHS offers it at 14–20 weeks.
-
This weekAmniocentesis Diagnostic
Diagnostic test on a small sample of amniotic fluid. Offered after a high-chance screening result. The NHS gives the miscarriage risk as about 1 in 200. A 2019 review estimated the added risk at about 0.3%.
Baby’s sex: Diagnostic, only done for medical reasons
-
From week 18Anatomy scan (anomaly scan) Ultrasound
A detailed ultrasound of the baby’s brain, heart, spine, face, kidneys, limbs and growth, plus the placenta position and fluid. The NHS usually does it at 18–21 weeks.
Baby’s sex: Sex usually visible if the baby’s position allows. Ask if your hospital reports it
Real size, next to an adult hand
Growth curve
When to call your midwife or doctor at 17 weeks
Call your midwife, doctor or maternity unit straight away, day or night, if you have any of these:
- Vaginal bleeding, or a gush or steady trickle of fluid.
- Severe belly pain that doesn’t go away.
- Regular tightenings, period-like cramps or lower back pressure that keep coming. This could be early labour.
- Fever of 38 °C (100.4 °F) or higher, or pain or burning when you pee.
- Pain or swelling in one leg, chest pain, or sudden shortness of breath. These can be signs of a blood clot.
- Feeling very low, hopeless or anxious most days. If you feel you might harm yourself, get emergency help.
Based on NHS and ACOG guidance. This list isn’t complete. If something feels wrong, call anyway. In an emergency, call your local emergency number.
Tip for this week
Plan the anatomy scan (18–22 weeks) if it isn’t booked yet, and decide whether you want to know the sex.
Myth or fact?
Do you need to eat for two when pregnant?
MythNo. The NHS says there’s no need to “eat for 2”. US guidance suggests no extra calories in the first trimester, about 340 extra a day in the second, and about 450 in the third.
Read the evidenceCommon questions at this stage
Questions people ask about week 17
How much should I eat in the second trimester?
US guidance suggests about 340 extra calories a day. The NHS says there’s no need to “eat for 2”. That is roughly a sandwich or a yoghurt with fruit and nuts. Your provider may advise differently based on your weight and health.
When do fingerprints form?
The first ridges start forming at around 10 to 11 weeks, and the pattern is largely set by about 16 to 17 weeks. It then grows larger over time.
References
- NHS Best Start in Life: 17 weeks pregnant
- NHS: Your antenatal appointments
- Mayo Clinic: Fetal development, the second trimester
- NHS: Your baby’s movements
- MedlinePlus (US National Library of Medicine): Fetal development
- US National Institute of Justice, The Fingerprint Sourcebook: Embryology of friction ridge skin
Advice differs between countries, so follow your own care team’s plan. Weights from week 20 are the WHO median, and earlier weights are approximate. How we check this.
All 40 weeks
First trimester Weeks 1–13
From conception to a fully formed, tiny fetus. The most rapid change of the whole pregnancy.
Second trimester Weeks 14–27
Growth, movement and senses. Often the most comfortable stretch for parents.
Third trimester Weeks 28–40
Weight gain, brain and lung maturation, and getting into position for birth.
