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

8 min read

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 20 weeks and 6 days, usually taking around 30 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.

Baby's length	About 25cm from head to heel
Baby's weight	Approximately 300 grams
Anomaly scan window	18 weeks to 20 weeks and 6 days
Scan length	Around 30 minutes, done abdominally
Uterus position	At the level of your navel

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.

Close-up of baby feet held by adult hands, symbolizing family love and care.

The 20-week anomaly scan: a guide

Your anomaly scan is a detailed NHS ultrasound offered to all women between 18 weeks and 20 weeks and 6 days. It usually takes around 30 minutes (longer if your baby is moving a lot or is not in the right position) and is carried out abdominally with gel on your bump. It looks for signs of 11 conditions. Most are physical differences in your baby's development and anatomy, but it also checks for signs of Edwards' syndrome and Patau's syndrome. It cannot find every condition.

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'll 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. You may be starting to feel your baby move, although in a first pregnancy you might not feel movements until after 20 weeks. Once you do, get to know your baby's usual pattern of movements. If your baby is moving less than usual, you cannot feel them moving anymore, or their usual pattern changes, call your midwife or maternity unit immediately. Do not wait until the next day, even if it's the middle of the night. If you have not felt your baby move by 24 weeks, tell your midwife.

When to get help

Some symptoms in pregnancy can be a sign of something serious and need checking quickly. This is who to contact, and how soon.

Call 999 if:

you're bleeding from your vagina and the bleeding is heavy (soaking a period pad soon after putting it on), or you also have severe pain in your tummy, pain in your shoulder, or feel sick, faint, dizzy or lose consciousness
you think your baby is coming now and you have a strong urge to push (ask for an ambulance)
you have severe difficulty breathing (you're gasping, choking or not able to get words out) or your chest feels tight or heavy
you have pain and swelling in one leg and you also feel short of breath or have chest pain. A blood clot in the leg can travel to your lungs, which can be life-threatening
you have possible signs of sepsis, such as breathing very fast, being confused or having slurred speech, blue, pale or blotchy skin, a rash that does not fade when you press it, or a very high or very low temperature. Being pregnant makes sepsis more likely
you do not feel you can keep yourself safe (a mental health emergency is as serious as a physical one)

Always call 999 if you think it's a life-threatening emergency, no matter what stage of pregnancy you are.

Call your midwife or maternity unit now if:

your baby is moving less than usual, you cannot feel your baby moving anymore, or there is a change to your baby's usual pattern of movements
you have light bleeding or spotting, even if you have no pain or only mild tummy pain
you have stomach pain that is severe or does not go away after you've rested for 30 to 60 minutes, or stomach pain with regular cramping or tightenings, lower back pain, or pain when you pee
you're less than 37 weeks pregnant and you have a gush or trickle of fluid from your vagina (this could be your waters breaking), regular contractions or tightenings, period-type pains, or backache that's not usual for you
you have signs of pre-eclampsia: a severe headache that does not go away with simple painkillers, vision problems (such as blurred vision or seeing flashing lights), pain below the ribs, sudden swelling of the face, hands or feet, feeling very unwell, heartburn that does not go away with heartburn medicines, or being sick (vomiting)
your skin is very itchy (for example, it keeps you awake at night), the palms of your hands or soles of your feet are itchy, or the itching is worse at night. This can be a sign of a liver condition called intrahepatic cholestasis of pregnancy (ICP) that needs urgent treatment
your breathlessness comes on suddenly, you're out of breath when you're lying down, or you're breathless and also have chest pain or feel dizzy
you have pain or swelling in one leg, usually in the calf or thigh. This could be a blood clot (deep vein thrombosis, or DVT), which is more likely when you're pregnant
you have a high temperature (38C or above), or you feel hotter than usual or shivery. A high temperature can be a sign of an infection, so it's important to get it checked

If your baby's movements change, do not wait until the next day: call immediately, even if it's the middle of the night. Do not use a home doppler to check the heartbeat yourself. Even if you hear a heartbeat, this does not mean your baby is well.

If you cannot reach them, or you're not sure what to do, call NHS 111.

Speak to your midwife or GP if:

you have not felt your baby move by 24 weeks. Most people start to feel movements between 16 and 24 weeks. If this is your first baby, you might not feel them until after 20 weeks
you're worried about your mental health, or stress, anxiety or low mood are affecting your day-to-day life. If you need urgent help for your mental health, call 111 and select the mental health option, or ask for an urgent GP appointment

Your week 20 checklist

This week:

Halfway there: things to do this week

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.

Sources: NHS, Tommy's, NCT, RCOG. General information, not medical advice.

Sources & further reading

General information, not individual medical advice. Speak to your GP, midwife or health visitor about your baby’s needs.