40 weeks pregnant
Your due week; your baby is about 51 cm and 3.4 kg.
Week 40 is your due week. Only a small proportion of babies are born exactly on this date; birth anywhere between weeks 37 and 42 is normal.
This week’s ultrasound image
Expected ultrasound appearance and measurements at week 40 (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)
51 cm
Head diameter
95 mm
Head circumference
339 mm
Femur length
74 mm
Estimated weight
3462 g
Heart rate
132 bpm
UA PI
0.75
How big is your baby this week?
About the size of a watermelon
What can be seen on the ultrasound?
BPD is about 95 mm, HC about 339 mm, AC about 352 mm and FL about 74 mm. The estimated weight is around 3,400 grams. The amniotic fluid and your baby’s wellbeing are assessed.
Your baby’s development
Your baby is about the size of a watermelon (about 51 cm from head to heel). All the organs are ready for life outside. With the first breath after birth, the lungs fill with air.
Changes in your body
Waiting can feel hard. Contractions, your waters breaking or a show could start at any moment.
Check-ups at this stage
- Checking your baby’s wellbeing with NST and ultrasound
- Assessing the cervix
- Discussing an induction plan if labour does not start (usually at week 41)
Tips for this week
- Keep a close eye on your baby’s movements
- Keep your hospital bag and documents with you
- Rest and keep drinking fluids
When should you see your doctor?
Go to the hospital if your waters break, or if you have bleeding, regular contractions, reduced baby movements, a fever, a severe headache or blurred vision.
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 happens if I go past 40 weeks?
Your doctor will monitor your baby’s wellbeing more often with NST and ultrasound. If labour does not start on its own, induction is usually recommended around week 41.
Will my baby arrive on the due date?
Only about 5 per cent of babies are born exactly on their due date. Most births happen between two weeks before and one week after it.
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