21 weeks pregnant
Your baby is about 27 cm and 360 grams; the kicks are getting stronger.
Week 21 is the first week of the second half of pregnancy. Your baby’s movements grow stronger and you can feel the kicks more clearly.
This week’s ultrasound image
Expected ultrasound appearance and measurements at week 21 (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)
26.7 cm
Head diameter
50 mm
Head circumference
188 mm
Femur length
35 mm
Estimated weight
360 g
Heart rate
144 bpm
How big is your baby this week?
About the size of a carrot
What can be seen on the ultrasound?
BPD is about 50 mm, HC about 188 mm, AC about 166 mm and FL about 35 mm. The estimated weight is around 360 grams. If the anomaly scan has not been done yet, it can still be done this week.
Your baby’s development
Your baby is about the length of a carrot (about 27 cm from head to heel). The taste buds have developed, so your baby can taste the amniotic fluid they swallow. Arm and leg movements become more coordinated.
Changes in your body
Varicose veins in the legs, mild ankle swelling and back pain may begin. Some mums-to-be feel irregular, painless tightenings (Braxton Hicks contractions).
Check-ups at this stage
- Anomaly scan (if not yet done)
- Routine check: blood pressure, weight, urine
- Planning the glucose tolerance test for weeks 24–28
Tips for this week
- Avoid standing for long periods; raise your legs when you sit down
- Walking for at least 30 minutes a day supports circulation
- Take iron-rich foods together with vitamin C
When should you see your doctor?
Contact your doctor if you have regular, painful contractions, bleeding, fluid leaking from the vagina or a clear reduction in your baby’s 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
What are Braxton Hicks contractions?
They are irregular, usually painless tightenings of the womb as it prepares for birth. They ease with rest or a change of position; if they become regular and painful, contact your doctor.
How much should the baby weigh at 21 weeks?
On average, around 360 grams. The estimated weight on ultrasound can vary by up to 15 per cent; your doctor assesses growth by looking at all the measurements together.
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