Detailed Fetal Anomaly Scan Home > Services We Offer
Ultrasound evaluation of the fetal anatomy may detect major structural anomalies. The 18-23 weeks of pregnancy is an ideal time to screen for these malformations although early diagnosis before 16 weeks is possible with higher resolution ultrasound machines.

This detailed scan looks at every part of the baby and will detect the large majority of major structural anomalies. The baby is systematically reviewed to from top to toe to look at the brain, face, spine, heart, lungs, diaphragm, stomach, kidneys, bowel and the upper and lower limbs. The baby will also be examined for chromosome markers or minor abnormalities of the normal anatomy, such as renal pelvis dilatation, talipes or echogenic bowel, that may be found in babies with a chromosomal abnormality. The placenta is located and measurements taken to verify the dates of the pregnancy and assess the baby's growth.

The scan is done using a trans-abdominal probe. It usually takes about 20 minutes. However, it may take a longer time particularly when the position of the baby is not ideal to look at certain organs of the body such as the heart when the baby's spine is anterior (facing up). Occasionally, the ultrasound scan may have to be rescheduled if the view of the baby is persistently difficult.
The objectives of screening for fetal abnormalities
Since its introduction more than 30 years ago, the ultrasound scan has become commonplace as a tool to obtain information about the baby in the womb. This is the result of its ability in obstetrics to provide diagnostic accuracy and a low false positive rate of 0.5%. In addition, compared to the other imaging modalities, it is cost effective and easy to use.

It is well known that about one in every 50 babies is born with a major structural abnormality. These fetal anomalies account for 15% of perinatal deaths and 15% of deaths in the first year of life. As antenatal and neonatal care improves, the impact of fetal malformations on survival becomes increasingly important and this forms the basis of ultrasound screening for fetal abnormalities.
Pregnancy can be an anxious time as many mothers worry about the normality of their babies. Since the majority of pregnancies do not encounter any problems, the ultrasound can positively reassure the mother of normality in her baby. Ultrasound will also enable the early diagnosis of major malformations such as anencephaly (baby without a brain), which are incompatible with life. Some anomalies that are amenable to intra-uterine therapy such as isolated hydrothorax (fluid in the lung) can be identified. Other malformations may warrant post-natal attention such as gastroschisis (a defect in the abdominal wall resulting in the gut outside the abdomen) needing surgery can also be easily identified.

However, one of the most important objectives of screening for fetal anomalies is parental preparation. Increasing knowledge of fetal life and the ability of the ultrasound scan to accurately diagnose fetal anomalies has aided the doctor to optimize management of the pregnancy and prognosticate fetal survival. The expected course of events will be discussed with parents. This will prepare them for any eventuality.
What are the abnormalities that can be detected?
Ultrasound scan can reliably detect many of the structural abnormalities (birth defects of the body structure) of the baby. Structural abnormalities which can be detected include hydrocephalus (swelling of the head with excessive fluid), anencephaly (absence of the brain), achondroplasia (dwarf), omphalocele (protrusion of the gut through an abdominal defect), spina bifida (defect in the spine), cleft palate / lips and heart defects (such as "hole in the heart").

Structural abnormalities such as congenital heart abnormalities may be associated with chromosomal problems like Down's syndrome. However, other structural malformations for example spina bifida are not associated with chromosomal problems. Some malformations may develop later, such as hydrocephalus (excess fuild in the brain) may not be apparent at the 18-23 weeks fetal anomaly scan but appear in the latter part of the pregnancy.
How reliable is ultrasound scan in the detection of fetal abnormalities?
Ultrasound is now widely used to detect fetal abnormalities in pregnancy. However, the detection rate of fetal abnormalities can vary widely, from 16% to 85%. The detection of severely and lethal anomalies is consistently better, between 60-86%.
[Crane JP, LeFevre ML, Winborn RC and the RADIUS study group; A randomised trial of prenatal u/s screening: impact on the detection, management and outcome of anomalous fetuses; AJOG 1994, Luck C; Value of routine ultrasound at 19 weeks - a 4 year study of 8849 deliveries; BMJ 1992].
This discrepancy in detection depends largely on the image quality of the subject, which in this case, is the baby. A better resolution or clearer image will improve the detection of abnormalities. A large patient is likely to give a poorer image quality because of ultrasound refraction and poor penetration as compared with a slim mother. Furthermore, the position of the fetus is crucial, for example, if the spine or vertebrae in anterior (pointing upwards), it would be extremely difficult to see the baby's heart due to the shadowing of the bony spine. However, this is the best position to visualize the baby's spine and kidneys.

In cases of oligohydramnios (reduced amniotic fluid in the womb), poor image quality results because the amniotic fluid provides a good media for ultrasound waves to travel. A more expensive machine will have more functions and improved resolution as compared with a lower cost machine. Finally, in order to improve the detection rate, the examiner must be experienced. In most countries, accreditation in ultrasound is not compulsory although many medical bodies are working hard towards some form of accreditation to ensure a minimum standard in ultrasound practice.

Certain anomalies are apparent at certain gestation and a routine 18-23 weeks scan may be entirely normal. An example would be ventriculomegaly or hydrocephalus where the fluid in the brain may accumulate and become excessive later in pregnancy. Therefore, in such cases, it is advisable to have a serial scan at different gestation. Other abnormalities may be difficult to detect at earlier gestation such as heart abnormalities. Visualizing the heart will be difficult at 15 weeks and therefore it is best to look at the heart structures during the 18-23 weeks fetal anomaly scan.
It is essential to use a
good and reliable
ultrasound machine
to obtain a good image
for accurate diagnosis
The following are some images of different parts of the baby during the detailed scan:
The 4-Chamber heart
Profile view of the fetal face
A view of the face showing the upper and lower lips of the baby.
A view of the back part of the baby's brain showing the cerebellum and the posterior fossa