Find out when each pregnancy ultrasound happens, from the dating scan to the anomaly and growth scans, and what every scan checks for you and your baby.
Dr. Bhanu Prakash
Ultrasound in pregnancy is one of the most reassuring parts of prenatal care. Hearing a heartbeat for the first time or watching a tiny hand flex on a grainy screen are moments expecting parents carry for life. Beyond the emotion, these scans serve a clear medical purpose: confirming that your pregnancy is progressing safely, catching problems early, and guiding the care you need at every stage.
Ultrasound imaging uses high-frequency sound waves to create real-time pictures of your uterus, placenta, and growing baby. No radiation is involved. A small probe, placed either on your abdomen or gently inside the vagina, sends sound waves that bounce off internal structures. A computer converts those echoes into images on a screen.
The main purposes are:
A typical pregnancy ultrasound schedule includes three to four planned scans across the trimesters, though your doctor may request additional scans based on your individual risk factors or medical history.
The dating scan in pregnancy is usually done between 6 and 9 weeks. Its primary job is confirming viability: is there a heartbeat, and is the pregnancy in the right location? A fetal heartbeat generally becomes detectable around 6 to 7 weeks. The sonographer measures the crown-rump length (CRL), the distance from the top of the baby's head to the base of its spine, which gives the most accurate estimate of gestational age and sets your expected due date.
If your periods are irregular or you conceived via IVF, this dating scan result becomes especially important because it anchors all future milestones in your pregnancy ultrasound schedule.
Between 11 weeks and 13 weeks plus 6 days is the window for the NT scan in pregnancy, also called the combined first trimester screen. The sonographer measures the fluid-filled space at the back of the baby's neck, known as the nuchal translucency. A thicker-than-expected measurement can indicate a higher risk of chromosomal conditions such as Down syndrome. This result is interpreted alongside a blood test (PAPP-A and free beta-hCG) and the mother's age to produce a risk ratio.
The NT scan also provides a first look at major structures including the brain, abdominal wall, and limbs, and can detect certain cardiac markers.
The anomaly scan, also called the mid-pregnancy anatomy scan or the 20-week scan, is the most detailed examination your baby receives in the womb. The anomaly scan week falls between 18 and 22 weeks, when the baby is large enough to visualise clearly but still small enough to fit on screen in full.
What the sonographer checks:
A note on fetal sex: Indian law under the Pre-Conception and Pre-Natal Diagnostic Techniques (PCPNDT) Act strictly prohibits disclosing a baby's sex during any prenatal scan. No ethical medical provider will share this information, and asking for it puts the provider in a difficult legal position.
If the baby's position makes imaging difficult, you may be asked to return for a repeat scan. This is routine and not a cause for concern.
From 28 weeks, the focus shifts to fetal growth and wellbeing. A growth scan in pregnancy measures the baby's head circumference, abdominal circumference, and femur (thigh bone) length, which together estimate fetal weight. These figures are plotted on a growth chart to confirm the baby is gaining weight within the expected range.
Serial growth scans at roughly 28, 32, and 36 weeks are common in higher-risk pregnancies, such as those complicated by hypertension, diabetes, multiple pregnancies, or a previous small-for-gestational-age baby.
Other than that, fetal breathing movements, muscle tone, and limb activity as part of a biophysical profile
When there are concerns about fetal growth, the doctor may request Doppler ultrasound. This measures blood flow in the umbilical cord and sometimes in the baby's brain to assess placental function. It is not part of every pregnancy ultrasound schedule, but it is an important tool when growth restriction is suspected.
| Type | When Used | How It Works |
| Transvaginal | Early pregnancy, usually before 10 to 12 weeks | Probe inserted gently into the vagina; gives clearer images when the uterus is still low in the pelvis. |
| Abdominal | From late first trimester onward | Probe moved over a gel-coated abdomen |
| Doppler | Second and third trimesters when blood flow assessment is needed | Measures direction and speed of blood |
A transvaginal scan is safe during pregnancy. It is often necessary in the first few weeks simply because the embryo is too small to be seen clearly from the outside.
The medical consensus, supported by decades of use worldwide, is that diagnostic ultrasound in standard clinical settings carries no known harm to the mother or baby. Unlike X-rays, it uses no ionising radiation.
That said, scans should be performed only when there is a clinical reason. Having scans done at commercial studios purely for keepsake images, outside a medical setting and without a trained operator, is not recommended. The concern is not proven harm but the absence of proper interpretation and the risk of false reassurance or unnecessary anxiety.
While ultrasound has no absolute contraindications in pregnancy, certain situations call for extra care or a specialist setting:
If you notice anything unexpected during or after a scan, or experience any discomfort, report adverse events to your healthcare provider or the relevant regulatory authority.
Routine pregnancy ultrasounds — dating, NT, anomaly, and growth scans — each serve a distinct purpose, from confirming viability and due dates to checking your baby's development and wellbeing at every stage. Diagnostic ultrasound performed for medical reasons is considered safe, but scan timing, frequency, and any additional monitoring should always be guided by your own doctor based on your individual pregnancy.
A low-risk pregnancy typically involves three to four ultrasound scans: a dating scan in the first trimester, an NT scan around 11 to 13 weeks, an anomaly scan between 18 and 22 weeks, and one or more growth scans in the third trimester. Your doctor may recommend more if any concerns arise.
Technically, fetal sex may be visible on an ultrasound from around 18 weeks onward, but disclosing it is prohibited in India under the PCPNDT Act. No registered medical provider will share this information.
The first ultrasound is usually done between 6 and 9 weeks to confirm the heartbeat and calculate the due date. If you have had bleeding, pain, or uncertainty about your dates, your doctor may arrange it earlier.
No harm from diagnostic ultrasound has been established in decades of clinical use. It uses sound waves, not radiation. Scans should still be done only for valid clinical reasons and by trained professionals.
A dating scan, done in the first trimester, confirms the pregnancy is viable and calculates your due date. An anomaly scan, done between 18 and 22 weeks, is a detailed anatomy check covering the baby's organs, brain, spine, heart, and placenta. They serve completely different purposes within your overall pregnancy ultrasound schedule.
