First-trimester ultrasounds: what each one looks for

The three scans

Dating or viability scan, around 6 to 9 weeks: confirms the pregnancy is inside the uterus, detects the heartbeat, counts how many babies there are, and dates the pregnancy. Early dating is the most accurate there is, and it sets the due date used for everything afterwards.

Nuchal translucency (NT) scan with the double marker blood test, 11 to 14 weeks: measures the fluid at the back of the baby's neck and combines it with blood results to estimate the risk of chromosomal conditions. It also checks early structure and, in twins, whether they share a placenta.

An additional early scan may be done for bleeding, pain, a previous ectopic or miscarriage, or uncertain dates.

Transvaginal versus abdominal: in early weeks a transvaginal scan gives a much clearer picture and is standard practice before about nine weeks. It is safe in pregnancy, including with bleeding, and it does not cause miscarriage.

What is visible when

By 5 weeks: a gestational sac. By 5 to 6 weeks: a yolk sac. From about 6 weeks: a fetal pole and usually a heartbeat.

7 to 8 weeks: a clear heartbeat, measurable crown-rump length, and early limb buds.

9 to 10 weeks: recognisable head and body, arm and leg movements, and the beginnings of fingers.

11 to 14 weeks: the NT measurement window, a visible profile, all four limbs, and the nasal bone assessed in many centres.

A scan done too early can show less than expected simply because of dates. A repeat in one to two weeks is a normal instruction rather than bad news.

Reading the report, and the law

Common terms: GS (gestational sac), YS (yolk sac), CRL (crown-rump length, used for dating), FHR or FHS (fetal heart rate or heart seen), and EDD (expected date of delivery).

'Single live intrauterine pregnancy' is the sentence most people are looking for: one baby, alive, in the right place.

If dates differ from your own calculation, the early scan usually wins — period-based dating assumes a textbook cycle that few women have.

One thing applies to every scan in India: determining or disclosing the sex of the fetus is a criminal offence under the PCPNDT Act, for the doctor, the clinic and the person who asks. The sonographer will not tell you, and asking puts them at risk of losing their registration.

When to see a doctor

Go to hospital immediately for heavy bleeding, severe or one-sided abdominal pain, fainting or dizziness, shoulder-tip pain, or fever with pelvic pain. Call 108 if you cannot travel quickly.

Same-day: any bleeding, cramping that is severe or one-sided, or a scan result you do not understand — take the report to your obstetrician rather than to the internet.

This article is general information, not medical advice, and is no substitute for personal medical advice. For any decision about your or your child's health, please consult your doctor.

Frequently asked questions

Q: Is ultrasound safe in early pregnancy? — Yes. Diagnostic ultrasound has been used for decades with no evidence of harm to the baby, and the standard schedule is safe. What is not useful is repeated scans without a clinical reason.

Q: Do I need a full bladder? — For an abdominal scan in early pregnancy, usually yes. For a transvaginal scan, an empty bladder. The clinic will tell you; follow their instruction.

Q: Can a scan miss a heartbeat that is there? — Very early, yes, usually because of dates or the position of the uterus. That is why a repeat scan in a week or two is often advised before any conclusion.

Q: How many scans will I have in total? — Usually four or five across the pregnancy in the standard schedule, more if there is a reason. Keepsake 3D scans add nothing medically.