Pregnancy ultrasounds can feel like separate appointments, each with a different name and purpose. Seen together, they form a timeline: early scans help establish dates and location, the mid-pregnancy scan looks closely at anatomy, and later scans may check growth, fluid, placenta, or the baby’s position when there is a clinical reason. The exact number of scans varies by healthcare system and individual pregnancy, so not everyone will have every scan described here.
First trimester: confirming dates and early development
An early ultrasound may be offered because of uncertain dates, pain or bleeding, fertility treatment, previous pregnancy complications, or routine first-trimester care. Depending on timing, it may be performed through the abdomen or with a transvaginal probe to obtain clearer images.
The dating ultrasound
A dating ultrasound is mainly used to estimate gestational age and establish an estimated due date. In England, the routine first scan is generally offered at 11 to 14 weeks. Measurements at this stage can be more reliable for dating than estimates based only on the last menstrual period, especially when cycles are irregular.
The sonographer may also confirm the number of babies, assess cardiac activity when it should be visible, check that the pregnancy is developing in the uterus, and review early development. With twins or higher-order multiples, the scan can also identify features that influence later monitoring.
Nuchal translucency and screening
Some first-trimester scans include a nuchal translucency measurement as part of screening for certain chromosomal conditions. This is screening, not a diagnosis, and options vary by location. If a result suggests a higher chance of a condition, the maternity team can explain follow-up screening or diagnostic tests.
Practical tip: if your clinic asks you to arrive with a full bladder, follow that instruction because it can improve the view during some abdominal scans. Preparation differs between services, so check your appointment information each time.
Second trimester: the detailed anatomy scan
The second trimester includes the scan many parents remember most clearly because the baby is large enough for a detailed structural assessment. In England, the 20-week screening scan is usually performed between 18 and 21 weeks, while guidance elsewhere commonly places the detailed examination around 18 to 22 weeks.
What the anatomy scan checks
The anatomy scan pregnancy appointment examines the baby’s developing structures in detail. The sonographer typically looks at the brain, spine, face, heart, abdomen, kidneys, limbs, and skeleton. The scan also assesses growth and placenta location. In the NHS screening programme, the 20-week scan screens for a defined group of physical conditions, but no ultrasound can detect every possible condition.
The appointment can take longer if the baby is in a position that makes certain views difficult. Being asked to walk around, return later, or attend a repeat scan does not automatically mean something is wrong; sometimes the sonographer simply cannot obtain all required images at the first attempt.
If something unexpected appears
When a finding needs clarification, parents may be offered another ultrasound, a specialist fetal medicine review, or additional testing. Some findings are normal variants, while others need closer assessment. A screening scan can identify a possible concern, but it does not always provide a final diagnosis on its own.
Useful related topics to explore include prenatal appointment schedule and prenatal screening tests, especially if you want to understand how ultrasound fits alongside blood tests and diagnostic procedures.
Third trimester: growth and wellbeing scans when needed
Not every uncomplicated pregnancy includes a routine third-trimester ultrasound. Additional scans are more likely when there is a reason to monitor growth or wellbeing, such as concerns about the baby measuring small or large, a low-lying placenta, multiple pregnancy, certain maternal health conditions, or findings from an earlier scan.
What a growth scan pregnancy appointment measures
A growth scan pregnancy assessment commonly includes measurements of the baby’s head, abdomen, and thigh bone. These are used to estimate fetal size and compare growth with the expected pattern for gestational age. Clinicians may also assess amniotic fluid, placenta location, and presentation. In selected situations, Doppler ultrasound may be used to assess blood flow in the placenta, umbilical cord, or fetal circulation.
One measurement does not tell the whole story. Growth is often interpreted as a pattern over time, especially when there is concern about fetal growth restriction. That is why a clinician may schedule repeat scans instead of drawing conclusions from one estimated weight.
Placenta position and baby’s presentation
If the placenta was low at the anatomy scan, a later ultrasound may check whether it has moved away from the cervix as the uterus grows. Ultrasound may also confirm whether the baby is head-down, breech, or in another position when that information affects birth planning.
A related guide on fetal movement and when to seek advice can be useful in late pregnancy. Ultrasound should not replace contacting your maternity team if you notice reduced movements, bleeding, significant pain, fluid loss, or other concerning symptoms.
How to think about your scan schedule
It is more helpful to think of scans as answers to clinical questions than as a fixed checklist. Early scans ask, “How far along is the pregnancy and is it developing where expected?” The anatomy scan asks, “How is the baby’s structure developing?” Later scans, when indicated, ask, “Is growth continuing appropriately, and are the placenta, fluid, blood flow, and position reassuring?”
This is why two people at the same stage may have different scan schedules. One may need only routine screening, while another may have extra ultrasounds because of twins, diabetes, blood pressure concerns, growth concerns, or a previous finding. Extra scanning does not necessarily mean there is a serious problem; often it is simply the safest way to collect more information.
Frequently asked questions
How many ultrasounds are normal during pregnancy?
There is no single number that applies everywhere. In England, at least two routine scans are generally offered at 11 to 14 weeks and 18 to 21 weeks. Other systems may use different schedules, and additional scans may be recommended for medical reasons.
Can an ultrasound detect every birth defect?
No. Ultrasound can identify many structural conditions, particularly during the detailed mid-pregnancy scan, but it cannot detect every condition and some abnormalities may not be visible before birth.
Is a third-trimester growth scan routine for everyone?
Not necessarily. Some services offer routine third-trimester scanning, while others reserve growth scans for pregnancies with specific risk factors or clinical concerns. Your maternity team can explain why a later scan is or is not recommended for you.
Are pregnancy ultrasounds safe?
Diagnostic ultrasound uses sound waves rather than ionising radiation. Professional guidance supports medically indicated ultrasound in pregnancy when it is used to answer a clinical question. Scans should be performed by trained professionals for medical benefit rather than used unnecessarily.
Putting each scan in context
Each ultrasound has a different job. The dating scan establishes the early timeline, the anatomy scan provides the most detailed structural review, and later growth or wellbeing scans add targeted information when closer monitoring is needed. Your own schedule may differ, so use this guide as a framework and ask your midwife, obstetrician, or sonographer what each scan is intended to check in your pregnancy.
