Most parents think of the 12-week scan as a chance to see their baby, confirm the due date and check that the pregnancy is progressing normally. It can, however, tell us much more.
By 12–13 weeks, most of the baby's major organs and body structures have already formed. With modern ultrasound and specialist expertise, a number of serious abnormalities can be identified weeks earlier than the traditional 20-week anatomy scan. Some can be diagnosed with confidence at this stage, while others need further examinations as the pregnancy progresses.
At The Pregnancy Clinic, we believe a detailed first-trimester scan should be more than a dating scan or a screening test for Down's syndrome: it is an important opportunity to assess your baby's early development.
Key points
- Up to about half of major fetal abnormalities can be identified at 11–13 weeks with a detailed, systematic examination.
- Severe abnormalities of the skull and brain, abdominal wall, bladder and limbs, and many major heart defects, can be recognised early.
- Detection depends on the type of condition, the quality of the scan and the expertise of the person performing it.
- A normal 12-week scan is reassuring, but the 20-week anatomy scan remains essential.
Can fetal abnormalities really be detected at 12 weeks?
Yes. There is considerable evidence that up to approximately half of major fetal abnormalities can be detected during the first trimester with a detailed ultrasound examination. Some are clearly visible at this stage, while others are harder to recognise because the organs are still small or continue to develop.
Detection depends on the type of condition, the quality of the ultrasound and the expertise of the person performing the scan. A detailed fetal medicine scan therefore provides considerably more information than a basic scan that measures the baby's size and nuchal translucency.
What are the advantages of assessing fetal anatomy at 12 weeks?
For the great majority of parents, a detailed assessment at the end of the first trimester provides early reassurance not only that the chance of a chromosomal condition is low, but also that the baby's development appears normal, with no major structural abnormality evident at this stage.
This offers confidence as parents enter the second trimester, knowing that they are considerably less likely to learn of a major or life-limiting condition for the first time halfway through the pregnancy at the 20-week scan.
In the small proportion of pregnancies in which an abnormality is identified, early diagnosis provides detailed information at a much earlier stage. This allows time for appropriate investigations, specialist counselling and careful consideration of how the pregnancy is best managed, before it is well advanced.
Which abnormalities can be detected?
The brain and skull
The skull and major brain structures can already be examined at 12 weeks. Serious conditions that can be identified include acrania (anencephaly), in which the skull and brain have not developed normally; holoprosencephaly, in which the brain has not divided into its normal right and left halves; and encephalocele, in which part of the brain or its coverings protrudes through an opening in the skull. Other brain abnormalities only become apparent later, as the brain continues to develop.
The spine and spina bifida
Spina bifida occurs when the baby's spine does not close completely during early development. At 12 weeks, major forms of open spina bifida can be suspected and detected, from changes in the spine and characteristic changes in the back of the developing brain. Smaller defects and closed forms of spina bifida require assessment later in pregnancy, which is why the spine is examined again at the 20-week scan.
The heart
Although the baby's heart is very small, its main chambers and blood vessels have already formed. Using high-resolution ultrasound and colour Doppler, we examine its structure and blood flow in detail. Major defects that can be detected at this stage include hypoplastic left heart syndrome, tricuspid atresia, pulmonary atresia, major forms of transposition of the great arteries and common arterial trunk.
Some heart defects are difficult to recognise at 12 weeks or only become apparent later, so a normal early heart examination is reassuring but the heart is always assessed again at 20 weeks.
The abdominal wall
Exomphalos occurs when some of the abdominal organs develop outside the abdomen, within a covering sac at the base of the umbilical cord; it can be associated with chromosomal or genetic conditions. In gastroschisis, part of the bowel lies outside the abdomen through an opening in the abdominal wall, without a protective sac.
Both can be identified in the first trimester. Because the bowel normally lies within the base of the cord until about 11–12 weeks, the findings are interpreted carefully in relation to the baby's size, and further assessment is needed to understand the severity and any associated problems.
The bladder and kidneys
One important finding at this stage is megacystis, an unusually enlarged bladder, which may indicate difficulty emptying it. When the bladder is only moderately enlarged and the chromosomes are normal, it often resolves spontaneously; a larger bladder is more likely to reflect a blockage that persists. Many other kidney and urinary tract abnormalities only appear later, so these organs are assessed again at subsequent scans.
The arms and legs
By 12 weeks the limbs are developed enough for us to assess their overall appearance. Major abnormalities that may be identified include transverse limb defects (limb amputations), in which part or all of an arm or leg is absent, and some forms of severe skeletal dysplasia (life-limiting forms of dwarfism), which cause marked shortening of the limbs and abnormal bone development, as well as major abnormalities of limb position. Smaller abnormalities of the hands, feet or individual bones may be difficult to recognise at this stage.
The face
Some major abnormalities involving the eyes, nose, jaw or overall facial development can be identified during a detailed first-trimester examination, and major facial clefts of the palate can be suspected and detected. Smaller clefts, particularly those affecting only the lip, are more reliably assessed later in pregnancy, so a normal facial examination at 12 weeks does not exclude every facial abnormality.
Can ultrasound identify signs of genetic conditions?
Yes. Some chromosomal and genetic conditions are associated with findings such as increased nuchal translucency, heart defects, or abnormalities of the brain, abdominal wall or limbs. Importantly, these may be present even when NIPT is reassuring: NIPT screens for selected chromosomal conditions, but it does not assess the baby's anatomy or exclude every genetic disorder. If a significant abnormality is identified, we will discuss diagnostic genetic testing, such as chorionic villus sampling (CVS) or amniocentesis, and arrange referral for this where appropriate.
For further information, read: NIPT vs Combined Screening: Which Test Should I Choose?
A routine scan and a specialist fetal medicine scan
The routine NHS 12-week scan is primarily intended to confirm the due date, identify the number of babies and offer screening for chromosomal conditions. Although some abnormalities may be noticed, it is not designed to provide a comprehensive examination of every fetal organ, and detection varies considerably between settings.
Our assessment goes further. As a fetal medicine-led clinic, every 12-week scan at The Pregnancy Clinic is performed by a consultant in fetal medicine and includes a systematic assessment of the baby's developing:
- Brain and skull, face and spine.
- Heart and major blood vessels.
- Abdominal wall, internal organs, bladder and urinary system.
- Arms and legs.
We also assess nuchal translucency and other ultrasound markers associated with chromosomal and genetic conditions. Even so, no 12-week scan, however detailed, can detect every fetal abnormality.
Detection of fetal abnormalities in pregnancy
Our three-stage approach: 12, 20 and 36 weeks
Babies develop throughout pregnancy: some abnormalities are visible early, while others only become apparent later. At The Pregnancy Clinic, we therefore recommend a three-stage ultrasound strategy.
11–13 weeks
The 12-week scan
Early detection of major structural abnormalities, including serious and life-limiting conditions, with time for specialist counselling and further investigations without delay.
20–22 weeks
The 20-week scan
A comprehensive, systematic assessment of the baby's anatomy, now larger and more developed, reassessing earlier findings and identifying abnormalities not yet visible at 12 weeks.
Around 36 weeks
The 36-week scan
A further anatomical review with assessment of growth and wellbeing, to identify conditions that develop later, for example of the brain, kidneys, bowel or heart, and plan care around birth.
No single scan can detect every fetal abnormality. The three examinations complement one another, maximising early detection while identifying conditions that only become apparent later.
If the 12-week scan is normal, do I still need the 20-week scan?
Yes. At 12 weeks the baby is not yet completely formed, and development continues throughout pregnancy, particularly of structures such as the brain. Some organs are still too small to assess in detail, and for others it is too early in pregnancy for a defect to be evident.
The 20-week scan is therefore an essential part of our three-stage approach to assessing fetal anatomy, with a further review at around 36 weeks.
What happens if an abnormality is detected?
We will explain the findings and provide you with detailed information and counselling, including whether further investigations are needed, such as a follow-up scan, a fetal heart assessment or genetic testing. Some conditions can be diagnosed with confidence at 12 weeks, while others need more information before their significance becomes clear.
We will liaise with your local NHS fetal medicine team to ensure timely sharing of the findings and onward management, and we will ensure that support for counselling is available if you need it. Early diagnosis gives you more time to understand the findings, consider your options and make informed decisions about your pregnancy.
Related pregnancy guides
Frequently asked questions
What abnormalities can be seen at the 12-week scan?
With a detailed examination, conditions such as acrania (anencephaly), holoprosencephaly, encephalocele, major forms of open spina bifida, many major heart defects, exomphalos, gastroschisis, megacystis and major limb abnormalities can be identified.
Can spina bifida be seen at 12 weeks?
Major forms of open spina bifida can be suspected and detected at 12 weeks. Smaller defects and closed spina bifida require assessment later in pregnancy, so the spine is examined again at 20 weeks.
Can heart defects be detected at 12 weeks?
Yes. In experienced hands, many major heart defects can be suspected or diagnosed at 12–13 weeks using high-resolution ultrasound and colour Doppler. The heart is always examined again at 20 weeks.
Can a 12-week scan detect a cleft lip or palate?
Major facial clefts involving the palate can be suspected and detected at 12 weeks, but smaller clefts, particularly of the lip alone, are more reliably assessed later in pregnancy.
If NIPT is normal, do I still need a detailed 12-week scan?
Yes. NIPT screens for selected chromosomal conditions but does not examine the baby's anatomy, so structural abnormalities can be present even when NIPT is reassuring.
Specialist pregnancy scans at The Pregnancy Clinic
At The Pregnancy Clinic, we provide consultant-led ultrasound examinations throughout pregnancy, with a particular emphasis on the early detection of fetal abnormalities. Our three-stage approach at around 12, 20 and 36 weeks combines detailed anatomical assessment with personalised advice, time to discuss the findings and continuity of care.
Where an abnormality is identified, we provide clear explanations and specialist counselling, and advise on appropriate investigations and further management, liaising with your local NHS fetal medicine team where needed.
Book a specialist 12-week scan →No ultrasound examination can guarantee the detection of every fetal abnormality. Detection depends on the nature of the condition, the stage of pregnancy and the quality of the examination. The Pregnancy Clinic provides planned appointments only; for urgent concerns, please contact your local NHS maternity unit, Early Pregnancy Unit, NHS 111 or your GP.
Clinical references
- Syngelaki A, Hammami A, Bower S, Zidere V, Akolekar R, Nicolaides KH. Diagnosis of fetal non-chromosomal abnormalities on routine ultrasound examination at 11–13 weeks' gestation. Ultrasound Obstet Gynecol. 2019;54(4):468–476.
- Minnella GP, Crupano FM, Syngelaki A, Zidere V, Akolekar R, Nicolaides KH. Diagnosis of major heart defects by routine first-trimester ultrasound examination: association with increased nuchal translucency, tricuspid regurgitation and abnormal flow in ductus venosus. Ultrasound Obstet Gynecol. 2020;55(5):637–644.
- Liao AW, Sebire NJ, Geerts L, Cicero S, Nicolaides KH. Megacystis at 10–14 weeks of gestation: chromosomal defects and outcome according to bladder length. Ultrasound Obstet Gynecol. 2003;21(4):338–341.
- Karim JN, Roberts NW, Salomon LJ, Papageorghiou AT. Systematic review of first-trimester ultrasound screening for detection of fetal structural anomalies and factors that affect screening performance. Ultrasound Obstet Gynecol. 2017;50(4):429–441.
- Bilardo CM, Chaoui R, Hyett JA, Kagan KO, Karim JN, Papageorghiou AT, et al. ISUOG Practice Guidelines (updated): performance of 11–14-week ultrasound scan. Ultrasound Obstet Gynecol. 2023;61(1):127–143.
- Fetal Medicine Foundation. The 11–13 weeks scan: early fetal anatomical assessment.
- NHS England. Fetal anomaly screening programme.