Pregnancy Week 20: The Anatomy Scan and Halfway Mark

Halfway there — baby is moving, and you're starting to show The week of the anatomy scan · Every organ checked · Sex reveal possible

Week 20 is the halfway point of pregnancy. Your baby is moving distinctly, and this is the standard window for the anatomy scan (Mid-Pregnancy Scan) — a detailed ultrasound that examines every major fetal structure.

Per ACOG [1] and the Royal Thai College of OB/GYN [2], a detailed ultrasound between 18–22 weeks is the global standard of prenatal care.

Your baby at week 20

Your baby is about 25 cm crown-to-heel and weighs roughly 300 grams — about the size of a large banana.

Key developments:

• Skin — vernix caseosa (a creamy white coating) protects skin in amniotic fluid
• Lanugo — soft fine hair covers the body, helping with temperature
• Fingerprints and toe-prints are fully formed
• Hair and eyebrows are starting to grow
• Nervous system + muscles are coordinated; quickening (first felt movements) often happens around now
• Hearing — your baby can hear sounds outside the womb and is starting to recognize your voice
• Swallowing and digestion — baby swallows amniotic fluid and produces meconium

Anatomy scan: what gets checked

Per ACOG [1], the mid-pregnancy ultrasound covers all major structures and takes about 30–45 minutes.

Structures examined

• Head and brain — head circumference, ventricles, choroid plexus, cerebellum
• Face — looking for cleft lip or palate
• Spine — checked along its full length for abnormalities like spina bifida
• Heart — 4-chamber view plus outflow tracts (valves and great vessels)
• Chest — lungs and diaphragm
• Abdomen — stomach, kidneys, bladder, abdominal wall
• Limbs — femur and humerus length, hands and feet
• Genitalia — sex can be determined fairly reliably (if you want to know)

Outside the baby

• Placenta — position, condition, thickness; checking for placenta previa
• Amniotic fluid — AFI (Amniotic Fluid Index), normally 5–25 cm
• Umbilical cord — number of vessels (normally 2 arteries, 1 vein)
• Cervix — cervical length, normally ≥ 25 mm

Self-care this week

Key nutrients

Per ACOG [1]:

• Iron — 27 mg/day to prevent anemia
• Calcium — 1,000 mg/day for baby's bones
• Protein — 71 g/day
• Omega-3 (DHA) — 200–300 mg/day for brain and eye development

Activity

• Start sleeping on your left side after week 20 — avoid lying flat on your back, which can compress major blood vessels
• Exercise — walking, swimming, prenatal yoga — 30 minutes 5 days a week
• Avoid — contact sports, fall-prone activities, hot tubs, saunas
• Air travel — generally safe through week 36, but check with your provider

When to seek care

• Vaginal bleeding at any volume
• Severe persistent abdominal pain or rhythmic uterine contractions
• Fluid leak from the vagina
• Reduced fetal movement after week 24 — even at week 20, if movement feels noticeably less, check in
• Facial, hand, or leg swelling with severe headache or blurred vision — possible pre-eclampsia signs
• Fever > 38.5°C (101.3°F)

Summary

Week 20 is the halfway mark, and the week of the all-important anatomy scan.

Care priorities:

1. Schedule the anatomy scan between 18–22 weeks with your OB
2. Switch to left-side sleeping — avoid lying flat on your back
3. Boost calcium, iron, and DHA
4. Stay active — 30 minutes of moderate activity 5 days a week
5. Start tracking fetal movement after week 24

If the scan finds anything unusual, ask for a referral to a Maternal-Fetal Medicine specialist for evaluation. Some conditions can be managed even in utero — early detection helps.