Microcephaly Ultrasound: Preparation, Procedure and Results

A microcephaly ultrasound is a prenatal scan that measures the fetus’s head and evaluates brain structures when the head appears smaller than expected. It is a screening and assessment tool rather than a diagnosis on its own, and follow-up imaging or testing may be recommended to understand the finding more clearly.

Overview: what a microcephaly ultrasound can show

A microcephaly ultrasound is a prenatal ultrasound examination used to measure the fetus’s head and assess whether it is smaller than expected for the stage of pregnancy. The sonographer measures the head circumference and other dimensions, then compares them with standardized reference charts. If the measurement is notably below the expected range, a clinician may consider possible fetal microcephaly.

Microcephaly describes a head size that is substantially smaller than average for age and sex. It can occur on its own or alongside differences in brain development, fetal growth or other organs. However, a small measurement on an ultrasound is not enough to confirm the condition. Head shape, family traits, uncertainty about gestational age and normal variation can all affect results.

The purpose of this assessment is to provide the clearest possible picture for the family and care team. It may include a detailed review of the brain, growth measurements and, when appropriate, follow-up testing. Results are best interpreted by a maternal-fetal medicine specialist or fetal imaging team in the context of the whole pregnancy.

How the ultrasound works and who may need it

Ultrasound uses high-frequency sound waves to create images of the fetus and placenta. A transducer placed on the abdomen sends and receives these sound waves, allowing the clinician to view fetal anatomy in real time. The examination does not use X-rays or other ionizing radiation.

A detailed microcephaly ultrasound may be recommended when a routine anatomy or growth scan shows a smaller-than-expected head circumference, when overall fetal growth is reduced, or when there are concerns about brain anatomy. It may also be offered when there is a family history of genetic conditions, a known maternal infection during pregnancy, exposure to certain substances or medications, or a previous pregnancy affected by a neurological or genetic condition.

In many cases, the finding is first noticed later in pregnancy because head growth can be more reliably followed over time. A specialist may schedule serial scans, often several weeks apart, to evaluate whether the head continues to grow along an expected pattern. The timing and frequency of follow-up are individualized.

Preparation, procedure and recovery timeline

Most patients do not need special preparation for a microcephaly ultrasound. The imaging center may provide instructions about whether to have a comfortably full bladder, particularly in early pregnancy. Wearing a two-piece outfit can make abdominal scanning more convenient. Patients may wish to bring prior ultrasound reports, genetic test results or details of relevant medical and family history.

During the procedure, the patient lies on an examination bed while gel is applied to the abdomen. The sonographer moves a handheld transducer over the skin to obtain views of the head, brain, abdomen, long bones and other structures. Measurements commonly include biparietal diameter, head circumference and abdominal circumference. In a detailed brain assessment, the specialist may examine structures such as the ventricles, cerebellum, corpus callosum and midline of the brain.

The scan is usually painless, although gentle pressure may be needed to obtain clear views. A detailed examination can take longer than a standard ultrasound, especially if fetal position makes imaging difficult. There is no physical recovery period: patients can generally return to normal activities immediately after the appointment.

Ultrasound is widely used in pregnancy and is generally considered safe when medically indicated and performed by trained professionals. Its main limitation is that image quality and diagnostic certainty can vary with gestational age, fetal position, maternal body habitus and the specific condition being assessed.

What are the ultrasound findings of microcephaly?

The central ultrasound finding is a fetal head circumference that is well below the expected range for the estimated gestational age. Clinicians may also assess the biparietal diameter, which measures the width of the head. A diagnosis is not based on a single number alone; the degree of difference, accuracy of pregnancy dating and change in measurements over time are all important.

Some fetuses with suspected microcephaly have otherwise typical ultrasound findings. In other cases, a detailed scan may show changes involving brain shape or structure, such as enlarged ventricles, altered development of the cerebral cortex, calcifications, an unusually small cerebellum or abnormalities of the corpus callosum. These findings are not present in every case and do not identify a cause by themselves.

The clinician also reviews the rest of the fetus for growth restriction, skeletal differences, heart abnormalities or other features that may guide further evaluation. If the scan raises concern, repeat targeted ultrasound, fetal neurosonography, fetal MRI, genetic counseling or carefully selected laboratory testing may be discussed. These additional assessments can help clarify the likely diagnosis and support pregnancy planning.

What are the signs of microcephaly in a fetus?

Microcephaly usually does not cause symptoms that a pregnant person can feel. Fetal movement, abdominal size and common pregnancy symptoms cannot reliably indicate whether a fetus has a small head size. It is generally identified through prenatal measurements rather than through physical signs noticed at home.

On imaging, the main sign is head growth that is smaller than expected for gestational age, particularly when the pattern persists or becomes more pronounced on later scans. The clinician may also look for a head size that is disproportionately small compared with the abdomen or femur length, although some fetuses are small overall because of constitutional size or fetal growth restriction.

It is important to avoid drawing conclusions from a single scan report. A suspected small head may reflect an early or uncertain due date, a temporary technical limitation, fetal head position or normal familial head size. Specialist review and follow-up measurements are the most useful next steps.

When to worry about fetus head size?

A fetal head measurement deserves further review when it is considerably below the expected range, when head growth slows across successive scans, or when there are additional differences in the brain or other organs. Concern may also be higher when there is a relevant family history, a suspected infection during pregnancy or known exposure to factors that can affect fetal development.

Even then, concern does not mean that an outcome can be predicted from ultrasound alone. Prenatal head measurements have limits, and the ability to identify microcephaly before birth is not perfect. A maternal-fetal medicine specialist can confirm gestational dating, repeat the measurements, compare growth proportions and explain what the findings do and do not mean.

Depending on the situation, the care team may discuss genetic counseling, diagnostic testing such as amniocentesis, maternal infection evaluation or fetal MRI. These options are voluntary and should be considered with clear counseling about their purpose, limitations and potential risks. The right plan depends on the stage of pregnancy and the individual findings.

At what age is microcephaly diagnosed?

Microcephaly may be suspected during pregnancy when ultrasound measurements show that the fetal head is substantially smaller than expected. Prenatal assessment can be particularly informative when measurements are repeated over time and a detailed evaluation of brain development is available. Still, prenatal ultrasound may not confirm every case.

After birth, clinicians measure the baby’s head circumference and compare it with standardized charts for age and sex. The measurement may be repeated during routine newborn and pediatric visits because head growth over time provides valuable information. Some children are diagnosed at birth, while others are identified later if their head growth does not follow the expected pattern.

When microcephaly is confirmed, the pediatric team may assess development, hearing, vision, muscle tone and feeding, and may recommend genetic, neurological or imaging evaluation when appropriate. Needs vary widely. Early developmental support can be beneficial for children who have developmental delays or other associated concerns.

Benefits, next steps and when to seek medical care

The main benefit of a microcephaly ultrasound is early, noninvasive information about fetal head growth and brain anatomy. It can help guide monitoring, specialist referrals and conversations about diagnostic options. Its limitations are equally important: no ultrasound result can fully predict a child’s development, and not every small fetal head represents a medical condition.

Pregnant people should contact their obstetrician or maternity unit promptly if they have been told that an ultrasound result is abnormal, have questions about a possible infection or medication exposure, or need help understanding recommended testing. Urgent maternity care is also appropriate for concerning pregnancy symptoms such as vaginal bleeding, leaking fluid, severe abdominal pain, fever or a noticeable reduction in fetal movement after movement has been established.

Acibadem International’s multidisciplinary specialists and JCI-accredited hospitals can assess fetal imaging findings and coordinate obstetric, maternal-fetal medicine, genetic and neonatal care for international patients. A clear discussion with a qualified clinician can help families understand the results, available follow-up and appropriate support.

Frequently asked questions

Is a microcephaly ultrasound accurate?

Ultrasound is an important tool for identifying a fetal head that measures smaller than expected, but it has limitations. Accuracy depends on gestational age, dating accuracy, fetal position, image quality and whether measurements are repeated over time. A specialist may recommend additional imaging or tests when results are concerning.

Can a small fetal head measurement be normal?

Yes. Some fetuses have a small head measurement because of normal family traits, uncertainty in pregnancy dating or natural variation in growth. A single measurement should be interpreted alongside the rest of the fetal growth assessment and, when needed, follow-up scans.

Does microcephaly ultrasound require a full bladder?

Usually, no special preparation is needed, especially later in pregnancy. Some facilities may ask patients to have a moderately full bladder for an early scan. The imaging center will provide any specific instructions before the appointment.

Can ultrasound determine the cause of microcephaly?

Ultrasound can identify patterns that may suggest an underlying cause, such as associated brain or growth differences, but it usually cannot determine the cause alone. Genetic counseling, infection testing, fetal MRI or diagnostic genetic testing may be considered depending on the findings.

Is fetal MRI always needed after an abnormal ultrasound?

No. Fetal MRI is not required for every small head measurement. It may be helpful when detailed ultrasound leaves uncertainty about brain anatomy or when additional brain findings need further clarification.

What happens if microcephaly is confirmed after birth?

The pediatric team will monitor head growth and evaluate the child’s overall health and development. Some children may need referrals to neurology, genetics, developmental services, hearing or vision specialists, depending on their individual needs. Early support and regular follow-up can help address concerns as they arise.

References

• World Health Organization
• Centers for Disease Control and Prevention
• International Society of Ultrasound in Obstetrics and Gynecology
• American College of Obstetricians and Gynecologists
• Society for Maternal-Fetal Medicine

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.