31 weeks pregnant
Your baby is about 41 cm and 1.5 kg; all five senses are working.
At week 31, all five of your baby’s senses are working. Your baby can turn their head from side to side and reacts to the world outside.
This week’s ultrasound image
Expected ultrasound appearance and measurements at week 31 (illustrative, to-scale drawing).
Abbreviations on the screen
- GS
- Gestational sac diameter
- YS
- Yolk sac
- CRL
- Crown–rump length
- NT
- Nuchal translucency
- BPD
- Biparietal diameter (head width)
- HC
- Head circumference
- AC
- Abdominal circumference
- FL
- Femur (thigh bone) length
- EFW
- Estimated fetal weight
- FHR
- Fetal heart rate (beats per minute)
- GA
- Gestational age (weeks + days)
- UA PI
- Umbilical artery Doppler resistance (PI)
Length (head to heel)
41.3 cm
Head diameter
80 mm
Head circumference
290 mm
Femur length
60 mm
Estimated weight
1502 g
Heart rate
137 bpm
UA PI
0.93
How big is your baby this week?
About the size of a coconut
What can be seen on the ultrasound?
BPD is about 80 mm, HC about 290 mm, AC about 274 mm and FL about 60 mm. The estimated weight is around 1,500 grams.
Your baby’s development
Your baby is about the size of a coconut. Nerve connections in the brain are multiplying rapidly. As fat builds up under the skin, your baby looks plumper.
Changes in your body
Braxton Hicks tightenings may be felt more often. A yellowish fluid (colostrum) may leak from your breasts.
Check-ups at this stage
- Routine check: blood pressure, weight, urine
- Growth and Doppler scan (if needed)
- Discussing your birth plan
Tips for this week
- Time your contractions: if they become regular, call your doctor
- Breast pads help with colostrum leaks
- Stay active with short walks
When should you see your doctor?
Before week 37, seek care straight away if you have more than 4 contractions an hour, bleeding, leaking fluid or reduced baby movements.
Growth by week
Values are averages; differences of a few days or a few millimetres between babies are normal.
| Pregnancy weeks | Crown–rump length (cm) | Weight (g) |
|---|---|---|
| Week 4 | — | — |
| Week 5 | — | — |
| Week 6 | 4 mm | — |
| Week 7 | 10 mm | — |
| Week 8 | 16 mm | 1 g |
| Week 9 | 23 mm | 2 g |
| Week 10 | 32 mm | 4 g |
| Week 11 | 43 mm | 8 g |
| Week 12 | 55 mm | 14 g |
| Week 13 | 68 mm | 23 g |
| Week 14 | 85 mm | 43 g |
| Week 15 | 100 mm | 70 g |
| Week 16 | 115 mm | 100 g |
| Week 17 | 128 mm | 140 g |
| Week 18 | 140 mm | 190 g |
| Week 19 | 152 mm | 240 g |
| Week 20 | 25.6 cm | 300 g |
| Week 21 | 26.7 cm | 360 g |
| Week 22 | 27.8 cm | 430 g |
| Week 23 | 28.9 cm | 501 g |
| Week 24 | 30 cm | 600 g |
| Week 25 | 31.9 cm | 660 g |
| Week 26 | 33.8 cm | 760 g |
| Week 27 | 35.6 cm | 875 g |
| Week 28 | 37.5 cm | 1005 g |
| Week 29 | 38.8 cm | 1153 g |
| Week 30 | 40 cm | 1319 g |
| Week 31 | 41.3 cm | 1502 g |
| Week 32 | 42.5 cm | 1702 g |
| Week 33 | 43.6 cm | 1918 g |
| Week 34 | 44.8 cm | 2146 g |
| Week 35 | 45.9 cm | 2383 g |
| Week 36 | 47 cm | 2622 g |
| Week 37 | 48 cm | 2859 g |
| Week 38 | 49 cm | 3083 g |
| Week 39 | 50 cm | 3288 g |
| Week 40 | 51 cm | 3462 g |
Frequently asked questions
Is it normal to leak colostrum?
Yes. Colostrum, your baby’s first food, may leak from the breasts in small amounts in the last months of pregnancy. It is also normal not to leak any.
How can I tell Braxton Hicks from real labour?
Braxton Hicks contractions are irregular and ease with rest. Real labour contractions come at regular intervals and get closer together and stronger.
Your pregnancy care at SoftCare Clinic
Book an appointment with our specialist doctors for your ultrasound check-up and any questions you may have.
The information on this page is for general guidance only and does not replace a medical examination. Measurements are average values; please discuss your own results with your doctor.
Medical content editor: Op. Dr. Şükrü Sanus