18 weeks pregnant
The anomaly scan window opens; your baby is about 14 cm and 190 grams.
Week 18 marks the start of the window for the detailed anomaly scan, when all of your baby’s organs are examined in detail.
This week’s ultrasound image
Expected ultrasound appearance and measurements at week 18 (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
140 mm
Head diameter
42 mm
Head circumference
152 mm
Femur length
27 mm
Estimated weight
190 g
Heart rate
148 bpm
How big is your baby this week?
About the size of a bell pepper
What can be seen on the ultrasound?
BPD is about 42 mm, HC about 152 mm, AC about 132 mm and FL about 27 mm. The brain, face, heart, kidneys, spine and limbs are examined one by one. The position of the placenta and the amniotic fluid are assessed.
Your baby’s development
Your baby is about the size of a bell pepper. The ears settle into position and your baby starts to hear sounds. Movements are getting stronger.
Changes in your body
You may start to feel your baby moving. Dizziness and leg cramps can occur.
Check-ups at this stage
- Anomaly scan (weeks 18–22)
- Routine check: blood pressure, weight, urine
- Antibody monitoring plan if you are Rh negative
Tips for this week
- Stand up slowly to prevent dizziness
- Stretching and drinking enough fluids help with leg cramps
- Talk to your baby: they are starting to hear your voice
When should you see your doctor?
Contact your doctor if you have bleeding, regular contractions, leaking fluid, 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
When is the anomaly scan done?
The best time is between weeks 18 and 22. At this stage, your baby’s organs are large enough to be examined in detail.
What is checked during the anomaly scan?
The brain structures, face and lips, heart chambers and vessels, spine, abdominal wall, kidneys, arms and legs, placenta and amniotic fluid are assessed.
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