Ultrasound can detect abnormalities at every stage of pregnancy

Pregnancy is a journey filled with both joy and anxiety, especially when it comes to the baby’s health and safety. Every mother dreams of ensuring that her baby is healthy, and ultrasound has become an essential tool for monitoring fetal health from the very early days of pregnancy.But did you know that each stage of pregnancy may reveal different types of fetal abnormalities through ultrasound?In this Daly Medical article, we will explain in a simple and clear way the abnormalities that can be detected by ultrasound during the first, second, and third trimesters of pregnancy. We will also discuss the best timing for detection and the most important tips to ensure accurate results.

What are fetal abnormalities?

Fetal abnormalities, also known as congenital anomalies, are any structural or functional changes that occur in the fetus during pregnancy. These changes may affect fetal growth, development, and the function of vital organs. Fetal abnormalities vary from mild conditions to severe and complex ones, and they may significantly impact the quality of life after birth.

Fetal abnormalities can result from genetic and environmental factors. Some genetic conditions are inherited within families, while environmental factors can also affect fetal health. For example, taking unprescribed medications or exposure to harmful chemicals may increase the risk of these abnormalities.

❓ Do all fetal abnormalities appear on ultrasound?

No. Ultrasound can detect major and obvious abnormalities such as spina bifida or cleft lip/palate.

However, subtle or internal abnormalities—such as small heart or kidney defects—may require additional tests or close follow-up.

❓ What is the difference between standard ultrasound and 4D ultrasound?

Standard ultrasound (2D):
A two-dimensional image that is effective in detecting most major abnormalities.

4D ultrasound:
A three-dimensional image with real-time movement of the fetus. It is better for detecting facial abnormalities, limb structure issues, and fetal movements more clearly.

❓ When is the best time to detect fetal abnormalities?

The detailed anomaly scan is usually performed between week 18 and week 22 of pregnancy, when fetal organs are well developed and visible.

4D ultrasound is preferably done between week 24 and week 32, when fetal movements and facial features are clearer.

❓ Does maternal weight affect ultrasound accuracy?

Yes. Abdominal fat can reduce image clarity.
Intestinal gas or an empty bladder in some cases may also affect scan quality.

❓ Is ultrasound safe for the fetus?

Yes, ultrasound is completely safe and does not involve radiation like X-rays.
It uses sound waves and does not cause pain or harm to the mother or fetus.

❓ Can diagnosis be wrong?

Yes, in some cases abnormalities may not be clearly visible.
Errors may occur due to fetal position, doctor experience, device quality, or maternal body factors.

❓ What should I do if an abnormality is detected?

The doctor usually refers the case to a fetal medicine specialist or pediatric surgeon before birth.
Additional tests or follow-up scans may be required for more accurate evaluation.

❓ Does ultrasound detect all genetic disorders?

No. Ultrasound mainly detects structural abnormalities, not all genetic or chromosomal disorders.

Some cases may require blood tests or genetic testing for a complete diagnosis.

Fetal abnormalities detectable by standard ultrasound

1️⃣ Nervous system abnormalities

Spina bifida: a defect in the spinal cord and vertebrae
Hydrocephalus: fluid buildup in the brain
Anencephaly: absence of major parts of the brain and skull

2️⃣ Cardiac abnormalities

Ventricular septal defect (VSD)
Atrial septal defect (ASD)
Valve malformations or obstructions

Minor defects may require detailed fetal echocardiography or follow-up scans.

3️⃣ Urinary system abnormalities

Kidney cysts or hydronephrosis
Absence of one kidney
Kidney malformations

4️⃣ Digestive system abnormalities

Abnormal stomach position or intestinal malformations
Intestinal obstruction
Major abdominal wall defects

5️⃣ Limb and bone abnormalities

Short or missing limbs
Finger or toe abnormalities (polydactyly or syndactyly)
Major bone deformities or fractures

6️⃣ Facial abnormalities

Cleft lip and palate (best seen in detailed scans)
Some visible eye or nasal abnormalities

7️⃣ Other major abnormalities

Abdominal wall defects or diaphragmatic hernia
Umbilical cord or placental issues

Risk factors for fetal abnormalities

1️⃣ Genetic factors

Family history of congenital disorders
Consanguineous marriage (cousin marriage)
Chromosomal disorders such as Down syndrome
Spontaneous genetic mutations

2️⃣ Maternal age

Pregnancy after age 35 increases the risk of chromosomal abnormalities.

3️⃣ Medications and chemicals

Certain drugs may be harmful during pregnancy, especially in the first trimester:

Unprescribed medications
Strong acne treatments
Some anti-epileptic drugs
Exposure to harmful chemicals or radiation

4️⃣ Infections during pregnancy

Rubella (German measles)
Zika virus
Toxoplasmosis (from raw meat or cats)

5️⃣ Poor nutrition

Folic acid deficiency (major cause of neural tube defects)
General vitamin and mineral deficiencies

6️⃣ Smoking and alcohol

Smoking reduces oxygen supply to the fetus
Alcohol can cause severe developmental and cognitive problems
Passive smoking is also harmful

7️⃣ Chronic maternal diseases

If uncontrolled:

Diabetes
Hypertension
Thyroid disorders

8️⃣ High body temperature exposure

Prolonged hot baths or saunas
High fever in early pregnancy

9️⃣ Radiation exposure

Unnecessary X-rays
Occupational exposure to radiation

Environmental factors

Pollution, pesticides, and heavy metals such as lead may also increase risk.

Factors affecting ultrasound accuracy

1️⃣ Equipment type

Modern ultrasound machines provide higher accuracy and better image quality.

2️⃣ Operator experience

The skill of the doctor or technician plays a major role in image quality and interpretation.

3️⃣ Maternal body weight

Excess abdominal fat may reduce image clarity.

4️⃣ Bladder and stomach condition

A full bladder may be required in early pregnancy; gas may reduce visibility.

5️⃣ Fetal age

Early pregnancy: small fetus, limited detail
Late pregnancy: large fetus, limited visibility of some structures

6️⃣ Fetal position

Fetal position may hide certain organs or structures.

7️⃣ Gas or air interference

Intestinal gas can reduce ultrasound clarity.

8️⃣ Diagnostic limitations

Some abnormalities are too small or early to detect and may require repeat scans or additional imaging such as MRI.

Fetal abnormalities detectable by 4D ultrasound

1️⃣ Facial abnormalities

Cleft lip and palate (clearly visible in 3D/4D imaging)
Jaw, nose, or eye malformations

2️⃣ Limb and bone abnormalities

Missing or short limbs
Extra fingers (polydactyly) or fused fingers (syndactyly)
Abnormal fetal movements or limb positioning

3️⃣ Nervous system abnormalities

Spina bifida: Sometimes detected through the appearance of the spinal column and fetal movements.
Hydrocephalus: Visible through enlarged head size and brain structure.
Anencephaly: Detected by abnormal or absent formation of the skull and brain.

4️⃣ Cardiac abnormalities

4D ultrasound allows visualization of fetal heart movement, but it is usually followed by a detailed Fetal Echocardiography for confirmation.
Major defects such as holes between the ventricles or atria (VSD / ASD) may be seen.

5️⃣ Urinary and digestive system abnormalities

Kidney cysts or hydronephrosis may sometimes appear clearly on ultrasound.
Abdominal wall defects or diaphragmatic hernia can be better diagnosed using 3D imaging.

6️⃣ Advantages of 4D ultrasound in detecting abnormalities

3D + real-time movement: Makes facial, limb, and movement abnormalities clearer than standard ultrasound.
Better movement assessment: Includes hand and foot movement, mouth opening and closing, and spinal motion.
Improved detection of external defects: Especially facial features, limbs, umbilical cord, and placenta.

How a standard ultrasound is performed

1️⃣ Preparation before the exam

Wear comfortable, loose clothing for easy access.
Drink water if pelvic or early pregnancy ultrasound is required to fill the bladder.
Avoid heavy meals for some abdominal scans.

2️⃣ Lying on the examination bed

The patient usually lies on her back or side depending on the area being examined.
A towel may be used to cover parts of the body.

3️⃣ Applying ultrasound gel

A special gel is applied to the skin to help sound waves travel smoothly without interference.

4️⃣ Using the transducer

The doctor moves a handheld device over the gel.
It sends high-frequency sound waves that reflect back as images on the screen.

5️⃣ Real-time imaging

Images appear instantly on the screen.
Still images or short videos may be recorded.
The patient may be asked to change position or breathe deeply.

6️⃣ After the scan

The gel is easily wiped off.
No pain or side effects occur.
The patient can return to normal activity immediately.

7️⃣ Results interpretation

The doctor explains the findings or provides a written report.
Sometimes follow-up scans are needed for confirmation.

Fetal abnormalities detected in the first trimester

1️⃣ Gestational sac abnormalities

Severe fetal abnormalities can sometimes be detected as early as week 7–8 using 3D ultrasound.
This includes early membrane rupture and conjoined twins.

2️⃣ Central nervous system development issues

Early brain and skull formation can be evaluated from around week 8.
The scan monitors normal CNS development and major abnormalities.

3️⃣ Trisomy 13 (Patau syndrome)

Detected between week 8–10 using 3D ultrasound.
Includes severe intellectual disability, facial deformities, brain and heart defects.

4️⃣ Noonan syndrome

May be suspected in early pregnancy.
Signs include cystic hygroma or neck swelling, similar to Turner syndrome.
May cause short stature, abnormal facial features, and heart defects.

5️⃣ Spinal defects

The spine appears as three parallel lines on 3D ultrasound.
Spina bifida may be detected around week 10 as an open spinal canal with exposed neural tissue.

6️⃣ Major cardiac defects

Some heart abnormalities, such as hypoplastic heart syndrome, may be detected around week 10.

7️⃣ Abdominal wall defects

Detected between weeks 9–11, including omphalocele or delayed abdominal wall closure.

8️⃣ Limb abnormalities

Fetal fingers can be seen from week 9–10.
Toe evaluation may be more difficult due to fetal position.

Ability of standard ultrasound to detect fetal abnormalities

Ultrasound is not only for viewing the fetus but is also a powerful tool for detecting congenital anomalies.

1️⃣ Ideal timing

Best performed between weeks 18–20 for maximum detection accuracy.

2️⃣ Imaging techniques

2D ultrasound: Primary tool for initial screening.
3D/4D ultrasound: Improves detection of facial and structural abnormalities and fetal movement assessment.