Your Essential Guide to Every Pregnancy Ultrasound on the NHS

A pregnancy ultrasound uses high-frequency sound waves to create images of your baby inside the womb, letting doctors check development and detect potential problems at each stage. In England, the NHS offers at least two routine scans during pregnancy: a dating scan around 12 weeks and an anomaly scan around 20 weeks. These scans are painless, have no known side effects, and give you the first real look at your growing baby. Whether you are pregnant through donor conception, co-parenting, or natural conception, understanding what to expect from each pregnancy ultrasound helps you feel prepared and in control.

CoParents.co.uk, a co-parenting and sperm donation platform with over 150,000 members since 2008, supports parents-to-be at every stage of the journey — from planning a family to navigating pregnancy care.

What Is a Pregnancy Ultrasound and How Does It Work?

A pregnancy ultrasound is a non-invasive imaging test that produces real-time black-and-white pictures of your baby. A device called a transducer is placed on your belly (or in some cases, inserted into the vagina for an early scan), and it sends sound waves through your body. These waves bounce off your baby’s tissues and are converted into images on a screen.

The procedure is safe for both you and your baby — no radiation is involved. A cold gel is applied to your tummy to help the sound waves travel more effectively and produce clearer images. Most scans take between 20 and 30 minutes, though this can vary if your baby is in an awkward position or moving a lot.

When Do You Have a Pregnancy Ultrasound on the NHS?

The NHS typically offers two routine pregnancy ultrasound appointments:

• The 12-week dating scan (usually between 10 and 14 weeks) to confirm your due date, check that the pregnancy is developing in the right place, and screen for Down’s syndrome if you choose.
• The 20-week anomaly scan (usually between 18 and 21 weeks) to check your baby’s physical development and screen for 11 specific conditions.

Some women may need additional scans depending on their health, age, or if complications arise. Women over 35, those carrying twins or multiples, and those with conditions like gestational diabetes are more likely to receive extra monitoring.

What Happens at the 12-Week Dating Scan?

The first routine pregnancy ultrasound is the 12-week dating scan. You will usually be asked to attend with a full bladder, as this helps the sonographer get a clearer image. The scan takes about 20 minutes and is performed by moving the transducer across your belly.

During this scan, the sonographer will confirm your baby has a heartbeat, measure the baby from head to bottom (crown-rump length) to estimate your due date, check whether you are carrying one baby or more, and confirm the pregnancy is developing inside the uterus rather than being ectopic.

If you choose to have screening for Down’s syndrome, Edwards’ syndrome, and Patau’s syndrome, the sonographer will also measure the fluid at the back of your baby’s neck — called the nuchal translucency. This measurement, combined with a blood test, calculates the probability of your baby having one of these conditions. This is a screening test, not a diagnosis — it tells you the chance, not the certainty.

For full details on what the dating scan checks, see the NHS 12-week scan guide.

What Does the 20-Week Anomaly Scan Check?

The second routine pregnancy ultrasound is the 20-week anomaly scan, usually performed between 18 and 21 weeks. This is the most detailed scan you will have during your pregnancy, and it typically lasts around 30 minutes — longer if you are carrying twins.

The sonographer will examine your baby’s brain, face, spine, heart, stomach, kidneys, bladder, limbs, and the umbilical cord. They check for signs of 11 specific conditions, including spina bifida, cleft lip, and congenital heart defects. The detection rate varies by condition — spina bifida is found in about 9 out of 10 cases, while heart defects are harder to spot, with roughly half detected at this stage.

The scan also checks the position of your placenta and the amount of amniotic fluid. If the placenta is lying low, you may need a follow-up scan at 32 weeks to check whether it has moved.

This is also the moment you can find out your baby’s sex — if you want to and if your hospital allows it. Be aware that the sonographer cannot guarantee 100% accuracy on gender.

For more on what the anomaly scan screens for, visit the NHS 20-week scan page.

Can You Have a Pregnancy Ultrasound in the First Trimester Before 12 Weeks?

The NHS does not routinely offer scans before 10 weeks, but an early pregnancy ultrasound may be recommended if you have bleeding, pain, a history of miscarriage, or conceived through IVF treatment.

An early scan, usually performed between 6 and 8 weeks, is often done transvaginally — a small probe is gently inserted into the vagina to get a closer look, since the baby is still very tiny at this stage. This type of pregnancy ultrasound can confirm the pregnancy is in the right place, detect a heartbeat (though this may not be visible before 7 weeks), and check for ectopic or molar pregnancy.

Don’t expect to see much detail at this early stage. Your baby will appear as a small dot or bean shape, typically measuring just 5 to 15 millimetres. The main purpose is reassurance and ruling out complications. Private early pregnancy scans at 7 to 8 weeks are increasingly popular for parents who find the wait until the 12-week NHS appointment difficult — particularly after previous miscarriage or fertility treatment.

Do You Need a Third Trimester Pregnancy Ultrasound?

Most women do not need another scan after the 20-week anomaly check. However, your doctor or midwife may recommend a third trimester pregnancy ultrasound if you are over 35, you are past your due date, there are concerns about your baby’s growth, the placenta was found to be low-lying at 20 weeks, or you have a condition like pre-eclampsia or gestational diabetes.

A third trimester scan typically checks amniotic fluid levels, the position of the baby and placenta, and estimated fetal weight. If your baby is in a breech position close to your due date, the scan helps your medical team plan for delivery.

Are Pregnancy Ultrasounds Safe?

Yes. Pregnancy ultrasound scans are considered safe for both you and your baby when performed by trained professionals in a clinical setting. Unlike X-rays, ultrasounds do not use radiation — they rely on sound waves, which have no known harmful effects. The NHS has been offering routine pregnancy ultrasound scans for decades, and extensive research has found no evidence of risk to mothers or babies.

The Royal College of Obstetricians and Gynaecologists and the Society and College of Radiographers both support the use of ultrasound as a standard part of pregnancy care. However, they advise against unnecessary or “keepsake” ultrasounds performed outside regulated clinical environments. If you do opt for a private scan for early reassurance, always choose a CQC-registered clinic with qualified sonographers.

Frequently Asked Questions

How many ultrasounds do you get during pregnancy on the NHS?

The NHS offers at least two routine scans: the 12-week dating scan and the 20-week anomaly scan. Some women receive additional scans if there are health concerns, complications, or if they are carrying multiples. Your midwife will advise if extra monitoring is needed.

Can a pregnancy ultrasound tell you the gender of your baby?

You may be able to find out your baby’s sex at the 20-week anomaly scan, but this depends on your hospital’s policy and your baby’s position during the scan. The sonographer cannot guarantee 100% accuracy, and some hospitals choose not to reveal gender at all.

Do pregnancy ultrasounds hurt?

No. A pregnancy ultrasound is painless. You may feel slight discomfort from the pressure of the transducer on your belly, especially if you have a full bladder. Transvaginal scans may feel unfamiliar but should not be painful.

What happens if the ultrasound finds a problem?

If the sonographer detects an abnormality or is unable to get clear images, you will usually be offered a follow-up appointment or referred to a specialist. Finding something on a scan does not always mean there is a serious problem — further tests are often needed to confirm any diagnosis. Your midwife and medical team will guide you through the next steps.

If you are planning a family and exploring your options, join CoParents.co.uk for free to connect with co-parents and donors who share your goals.