12 weeks pregnant
The ideal week for the NT scan and combined test; CRL is about 5.5 cm.
Week 12 is when first-trimester screening is most commonly done. Your baby’s whole body fits into a single ultrasound image.
This week’s ultrasound image
Expected ultrasound appearance and measurements at week 12 (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
55 mm
Nuchal translucency
1.3 mm
Head diameter
20 mm
Estimated weight
14 g
Heart rate
160 bpm
How big is your baby this week?
About the size of a lime
What can be seen on the ultrasound?
CRL is about 50–60 mm and head diameter (BPD) about 20 mm. The profile, nasal bone, stomach, bladder, arms and legs can be seen. The heart rate is about 160 beats per minute. The bowel has returned into the abdomen.
Your baby’s development
Your baby is about the size of a lime and weighs around 14 grams. Reflexes are developing: your baby can open and close their fingers and moves when touched. The kidneys are producing urine.
Changes in your body
Your womb rises above the pelvic bone, so you may need to pass urine less often. Nausea eases for many people.
Check-ups at this stage
- NT scan and combined test
- Blood pressure, weight and urine monitoring
- Discussion of NIPT, CVS or amniocentesis if needed, depending on results
Tips for this week
- Talk to your doctor about healthy weight gain in pregnancy
- You can start regular gentle exercise (if your doctor agrees)
- Choose fish rich in omega-3 and low in mercury
When should you see your doctor?
Contact your doctor if you have bleeding, one-sided pain, a fever or a burning sensation when passing urine.
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 is the combined test?
It measures PAPP-A and free beta-hCG levels in the mother’s blood. Combined with the NT measurement, it is used to calculate the risk of chromosomal conditions such as Down syndrome.
Can the baby’s sex be seen at 12 weeks?
Sometimes it can be guessed, but not reliably. The baby’s sex is usually seen more clearly on ultrasound at weeks 16–20.
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