Pregnancy Ultrasound Schedule in Bangkok: Which Scan, When, and What It Shows

Prenatal imaging guide · 2026

Ultrasound answers the questions blood tests cannot. The anomaly scan in particular has no substitute, whatever your NIPT said.

By MedEx · Updated September 2026 · Approx. 8-minute read

Quick answer

A typical pregnancy involves several ultrasound examinations, each with a distinct job. The dating scan (roughly 6–10 weeks) confirms viability, gestational age and the number of fetuses. The nuchal translucency scan (11–14 weeks) measures nuchal thickness and assesses early structure. The anomaly scan (18–22 weeks) is the most detailed structural examination and has no substitute — NIPT does not assess structure at all. Growth scans in the third trimester assess growth, fluid, placental position and fetal wellbeing where indicated.

In this guide

1. The dating scan
2. The nuchal translucency scan
3. The anomaly scan
4. Third trimester and additional scans

The dating scan

Performed roughly between 6 and 10 weeks, this scan establishes the foundations for everything else:

• Viability — confirming a fetal heartbeat.
• Location — confirming the pregnancy is intrauterine, which matters because ectopic pregnancy is a medical emergency.
• Gestational age — crown-rump length dating in the first trimester is more accurate than dating from the last menstrual period.
• Number of fetuses and chorionicity — and chorionicity is most reliably determined early, which is why a late first scan loses information permanently.

All of this feeds into NIPT interpretation, which is why a dating scan before the blood draw is advisable — see the NIPT timing guide.

The nuchal translucency scan

Performed between 11 and 14 weeks, when the measurement is valid. It contributes to combined screening, but its value is broader than that.

An increased nuchal translucency is associated with chromosomal conditions, but also — independently of chromosomes — with congenital heart defects, skeletal dysplasias and several genetic syndromes. This means an increased NT with a low-risk NIPT is not reassuring, and should prompt detailed cardiac assessment and often diagnostic testing with chromosomal microarray.

The scan also provides an early structural survey: many major abnormalities, including some cardiac, abdominal wall and skeletal findings, are visible at this stage. Comparison with combined screening is covered in the NIPT versus combined screening guide.

The anomaly scan

Performed between 18 and 22 weeks, this is the detailed structural examination and the single most important scan of the pregnancy. It systematically assesses:

Detection is not complete. Some conditions develop later, some are not visible on ultrasound at all, and image quality is affected by fetal position and maternal body habitus. But nothing else covers this ground — and a low-risk NIPT is not a reason to skip it. Book through MedEx imaging services.

Third trimester and additional scans

Growth scans assess estimated fetal weight, amniotic fluid and, where indicated, Doppler blood flow. They are commonly arranged where there are risk factors such as a low PAPP-A, hypertension, diabetes, a small or large fundal height, reduced fetal movements or a previous growth-restricted baby.

Placental localisation is repeated where the placenta was low-lying at the anomaly scan, since most resolve as the uterus grows.

Cervical length may be measured where there is a history of preterm birth.

Presentation is confirmed towards term, since clinical examination alone is unreliable.

A note on 3D and 4D scans: these are largely for parental experience rather than diagnosis, and they do not replace the standard 2D assessment. There is no evidence of harm from diagnostic ultrasound at standard settings, but professional bodies advise against non-medical use.

Plan the schedule with your obstetric team, or arrange scans and a review through MedEx imaging and a doctor consultation.

Frequently asked questions

How many ultrasound scans are needed in pregnancy?

Typically a dating scan at roughly 6 to 10 weeks, a nuchal translucency scan at 11 to 14 weeks, an anomaly scan at 18 to 22 weeks, and third trimester growth scans where clinically indicated.

Do I need an anomaly scan if my NIPT was low risk?

Yes. NIPT does not assess fetal structure at all, so the anomaly scan covers entirely different ground including the heart, brain, spine, kidneys and limbs.

What does an increased nuchal translucency mean?

It is associated with chromosomal conditions but also, independently of chromosomes, with congenital heart defects, skeletal dysplasias and several genetic syndromes. A low-risk NIPT does not make an increased NT reassuring.

When is the dating scan done?

Roughly between 6 and 10 weeks. It confirms viability and location, establishes gestational age more accurately than menstrual dates, and determines the number of fetuses and chorionicity.

Are 3D and 4D scans medically useful?

They are largely for parental experience rather than diagnosis and do not replace standard 2D assessment. Professional bodies advise against non-medical use of ultrasound.

Can the anomaly scan detect everything?

No. Some conditions develop later in pregnancy, some are not visible on ultrasound, and image quality is affected by fetal position and maternal body habitus. It remains the most comprehensive structural assessment available.

Sources and further reading

1. ISUOG practice guidelines: mid-trimester fetal ultrasound scan
2. ACOG Practice Bulletin: Ultrasound in Pregnancy
3. MedEx imaging services

Medical disclaimer: This article is general health information and does not replace medical advice, diagnosis or treatment. Laboratory reference ranges differ between laboratories and results must be interpreted alongside your symptoms, medicines and medical history. Speak with a qualified clinician before starting, stopping or changing any treatment. Service details, inclusions and prices can change — confirm them with MedEx before booking.