Author: Dr. Ayesha Siddiqa
Pregnancy is a beautiful journey filled with anticipation, excitement, and many important milestones. One of the most valuable tools used throughout pregnancy is ultrasound scanning, which allows your obstetrician to monitor your baby's growth, development, and overall wellbeing.
Many parents-to-be wonder,
"How many scans will I need?" or "What does each scan check?" Understanding the purpose of each
pregnancy scan can help you feel more informed and confident during your pregnancy.
What Is a Pregnancy Ultrasound?
An ultrasound scan uses high-frequency sound waves to create images of your baby and the structures inside the uterus. Unlike X-rays, ultrasound does not use radiation, making it a safe and routinely used investigation during pregnancy when performed by trained healthcare professionals.
The number of scans you need depends on your individual pregnancy. Women with
high risk pregnancies may require additional ultrasounds based on their doctor's recommendations.
1. Early Pregnancy (Dating and Viability Scan)
When is it done?
Around 6 to 9 weeks of pregnancy.
Why is it performed?
- Confirm that the pregnancy is inside the uterus.
- Detect your baby's heartbeat.
- Estimate the gestational age and expected due date.
- Determine whether you are carrying one baby or twins (or more).
- Assess the cause of early pregnancy bleeding or pain if present.
An
early pregnancy scan is often the first time parents see their baby, and it sets the timeline for the rest of your antenatal care.
2. NT Scan (Nuchal Translucency Scan)
When is it done?
Between 11 weeks and 13 weeks plus 6 days.
Why is it important?
- Measures the fluid-filled space at the back of the baby's neck.
- Forms part of the first-trimester screening for certain chromosomal conditions, such as Down syndrome.
- Assesses early fetal anatomy.
- Confirms gestational age.
The
NT scan is often combined with maternal blood tests for a more accurate assessment. It is a screening test, which means it estimates the chance of a condition rather than confirming it.
3. Early Anomaly Scan
When is it done?
Around 13 to 16 weeks, in selected pregnancies.
Purpose
- Provides an early assessment of developing fetal organs.
- May detect certain major structural abnormalities.
- Usually recommended in women with specific medical or pregnancy-related indications.
It does not replace the detailed anomaly scan performed later in pregnancy.
4. Anomaly Scan (Level II Scan)
When is it done?
Between 18 and 22 weeks.
This is one of the most important scans during pregnancy.
It carefully examines your baby's:
- Brain
- Face
- Spine
- Heart
- Lungs
- Kidneys
- Stomach
- Limbs
- Abdomen
It also evaluates:
- Placental location
- Umbilical cord
- Amniotic fluid
- Cervical length
- Baby's growth
The anomaly scan helps identify many structural abnormalities and guides further evaluation if required.
5. Growth Scan
When is it done?
Usually between 28 and 32 weeks, or as advised by your obstetrician.
What does it assess?
- Baby's growth and estimated weight.
- Head, abdominal, and femur measurements.
- Amniotic fluid volume.
- Placental position and appearance.
- Baby's presentation (head down, breech, or transverse).
Growth scans are particularly important in pregnancies complicated by diabetes, hypertension, twin pregnancy, or concerns regarding fetal growth.
6. Doppler Scan
When is it recommended?
Usually during the third trimester if medically indicated.
Purpose
A Doppler ultrasound evaluates blood flow between:
- Mother and placenta.
- Placenta and baby.
- Baby's major blood vessels.
It is commonly advised when there is:
- High blood pressure
- Fetal growth restriction
- Reduced fetal movements
- Twin pregnancy
- Certain maternal medical conditions
This scan helps doctors determine whether the baby is receiving adequate oxygen and nutrients.
7. Biophysical Profile (BPP)
When is it performed?
Generally in the third trimester for selected pregnancies.
The Biophysical Profile combines an ultrasound assessment with fetal heart rate monitoring to evaluate:
- Baby's movements
- Muscle tone
- Breathing movements
- Amniotic fluid volume
- Overall fetal wellbeing
It is commonly used when additional monitoring is needed.
8. Placental Localisation Scan
If the placenta is found to be low-lying during the mid-pregnancy scan, a repeat ultrasound is often performed around
32 to 34 weeks to determine whether it has moved away from the cervix. This information is important when planning the safest mode of delivery.
Are Frequent Ultrasounds Safe?
Ultrasound has been used in obstetric care for several decades and is considered safe when performed for medical indications by trained professionals. Routine pregnancy scans are recommended because they provide valuable information about both maternal and fetal health.
Can a Scan Detect Every Problem?
While modern ultrasound technology can identify many fetal abnormalities, no scan can guarantee that every condition will be detected. Some conditions may develop later in pregnancy or may not be visible on ultrasound. Where a finding needs closer assessment, your obstetrician may refer you to a
fetal medicine specialist.
Regular
antenatal checkups, blood investigations, and following your obstetrician's advice remain equally important for a healthy pregnancy.
Key Takeaway
Each ultrasound scan has a unique purpose and plays an important role in monitoring your pregnancy. From confirming your baby's heartbeat in early pregnancy to assessing growth and wellbeing in the third trimester, these scans help ensure that both mother and baby receive the best possible care.
If you have questions about any scan recommended during your pregnancy, speak with your obstetrician. Understanding why each scan is performed can help you feel reassured and actively involved in your prenatal care.
Frequently Asked Questions
How many scans are done during pregnancy?
Most women have three to four scans in an uncomplicated pregnancy: an early dating scan, the NT scan, the anomaly scan, and often a growth scan in the third trimester. The exact number depends on your health, your baby's growth, and your obstetrician's advice.
When is the first scan done in pregnancy?
The first scan is usually done between 6 and 9 weeks of pregnancy. It confirms that the pregnancy is inside the uterus, detects the baby's heartbeat, estimates your due date, and checks whether you are carrying one baby or more.
Is ultrasound safe during pregnancy?
Yes. Ultrasound uses sound waves rather than radiation and has been used in obstetric care for several decades. It is considered safe when performed for medical reasons by trained professionals.
What is the difference between an NT scan and an anomaly scan?
The NT scan is done between 11 weeks and 13 weeks plus 6 days and screens for the chance of certain chromosomal conditions. The anomaly scan is done between 18 and 22 weeks and examines your baby's organs and structure in detail. They serve different purposes.
Can a pregnancy scan reveal the baby's gender?
No. Determining or disclosing the sex of an unborn baby is prohibited by law in India under the PCPNDT Act. Pregnancy scans are performed solely to assess your baby's health, growth, and development.
Do I need a full bladder before a pregnancy scan?
It depends on the scan and the stage of pregnancy. A full bladder is often advised for early scans because it helps produce clearer images. Later scans usually do not require this. Your healthcare provider will advise you before your appointment.
How long does a pregnancy scan take?
Most routine scans take around 20 to 30 minutes. The anomaly scan often takes longer because your baby's organs are examined in detail. If your baby is in an awkward position, you may be asked to walk around and return, which can extend the appointment.
Why do some women need more scans than others?
Additional scans are advised when closer monitoring is beneficial. This includes pregnancies affected by diabetes, high blood pressure, twins, previous complications, or concerns about your baby's growth or movements.
What happens if a scan shows something abnormal?
Your obstetrician will explain the findings and what they may mean. Some findings require only a repeat scan, while others may need further testing or referral to a fetal medicine specialist.
Can a scan detect every birth defect?
No. Ultrasound identifies many structural abnormalities, but no scan can detect every condition. Some develop later in pregnancy, and others are not visible on ultrasound. Regular antenatal visits, blood tests, and following your obstetrician's recommendations remain essential.
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