Pregnancy Week 20: Your 20-Week Anomaly Scan — What to Expect

Quick answer: At 20 weeks you are halfway, and this is the week of the NHS anomaly scan — a detailed ultrasound offered between 18 weeks and 21 weeks and 1 day, taking about 30 to 45 minutes. The sonographer checks your baby's skull, brain, face, heart, spine, abdominal wall, kidneys, limbs and placental position. Your baby is around 25cm head to heel and weighs about 300 grams.

What parents need to know

Halfway! You are now 20 weeks pregnant, which means you've reached the midpoint of your pregnancy. This week brings the eagerly awaited anomaly scan — one of the most significant appointments of your pregnancy — and a chance to see your baby in wonderful detail. You're also officially halfway through your 40-week journey.

How big is your baby at 20 weeks?

At 20 weeks, your baby is about 25cm from head to toe — measurements are now taken from crown to heel rather than crown to rump, as the legs are now fully extended. Your baby weighs approximately 300 grams.

What's happening with your baby?

Your baby is now swallowing amniotic fluid regularly, and their digestive system is practising for the outside world. The first fetal stool — called meconium — is beginning to build up in the intestines. This dark, sticky substance is usually passed in the first day or two after birth, though occasionally babies pass it before birth in the amniotic fluid, which the midwife team will monitor carefully.

Your baby's skin is still thin and covered in vernix (the waxy protective coating) and lanugo (fine body hair). Beneath the skin, fat is very slowly beginning to accumulate. Your baby's senses are well developed: they can hear clearly, detect light, taste the amniotic fluid, and respond to touch.

The 20-week anomaly scan: a guide

Your anomaly scan is a detailed NHS ultrasound offered to all women between 18 weeks and 21 weeks and 1 day. It takes approximately 30 to 45 minutes and is carried out abdominally with gel on your bump. It is NOT a routine screening test for chromosomal conditions — rather, it examines your baby's physical development and anatomy in detail.

What the sonographer checks

The sonographer examines your baby's skull and brain (checking for conditions such as anencephaly and spina bifida), face (looking for cleft lip), heart (checking all four chambers and major blood vessels), spine (vertebrae alignment), abdominal wall, kidneys and bladder, limbs (checking for the presence and length of long bones), and placental position.

Standard measurements are also taken: head circumference, abdominal circumference, and femur length. These are plotted on a growth chart to confirm your baby is growing as expected.

If something is found

Most anomaly scans are reassuringly normal. However, occasionally a finding will require further investigation. If something is flagged, try to remember that many findings are minor and resolve naturally, or are much less serious than they first sound. You will be referred to a consultant or specialist midwife for further discussion and, if needed, additional tests. Taking a support person to the scan and having contact details for your midwife team is helpful in case you receive unexpected news.

Finding out your baby's sex

This is the scan at which you may find out whether you're expecting a boy or a girl, if you want to. Not all NHS trusts routinely offer this, and it's not always possible to determine reliably depending on how your baby is lying. If you do want to find out, ask the sonographer before the scan begins. Of course, you are under no obligation — many parents choose to be surprised at the birth.

What's happening in your body?

At 20 weeks, your uterus is at the level of your navel. Your bump is well established, and from this point it will continue to grow noticeably week by week. Baby movements should be becoming more regular and recognisable. From 28 weeks, the NHS will ask you to monitor your baby's movements more closely, but for now, simply enjoy getting to know your baby's patterns.

Your week 20 checklist

This week:

• Attend your 20-week anomaly scan.
• Decide whether you want to find out your baby's sex.
• Celebrate reaching the halfway point.
• Continue monitoring your baby's movements.
• Begin thinking about your birth plan and preferences for the birth.