13 weeks pregnant
The last week of the first trimester; CRL is about 6.8 cm.
Week 13 is the last week of the first trimester. The risk of miscarriage falls considerably, and many mums-to-be start to feel more energetic.
This week’s ultrasound image
Expected ultrasound appearance and measurements at week 13 (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)
Crown–rump length
68 mm
Nuchal translucency
1.5 mm
Head diameter
24 mm
Estimated weight
23 g
Heart rate
158 bpm
How big is your baby this week?
About the size of a lemon
What can be seen on the ultrasound?
CRL is about 65–70 mm and BPD about 24 mm. The NT measurement can be done up to 13 weeks and 6 days. Your baby’s hand and foot movements can be watched in real time.
Your baby’s development
Your baby is about the size of a lemon and weighs around 23 grams. Fingerprints begin to form and the vocal cords are developing. The bowel is now fully back inside the abdomen.
Changes in your body
For most people nausea eases and energy increases. Your bump may start to show slightly.
Check-ups at this stage
- Last chance for the NT measurement (13 weeks + 6 days)
- Reviewing combined test results
- Routine blood pressure and urine check
Tips for this week
- Keep track of your weight regularly
- Start getting used to sleeping on your side rather than on your back
- Look into pregnancy exercise or yoga classes
When should you see your doctor?
Contact your doctor if you have bleeding, abdominal pain, a fever or fluid leaking from the vagina.
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
Does the risk of miscarriage fall after week 13?
Yes. Most miscarriages happen in the first 12 weeks; after this point, the risk falls considerably.
What if I miss the NT scan?
NT cannot be measured after 13 weeks and 6 days. Your doctor may suggest NIPT or the quadruple test at weeks 15–20 instead.
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