PUBLIC INFORMATION

Visualization of organs and abnormalities in these organs by ultrasound is dependent on many factors like obesity, presence of wounds, bandages etc., which may limit visualization and some abnormalities may not be seen.
Some organs like gallbladder, pancreas are best seen in fasting state while pelvic organs are seen with full urinary bladder. Inadequate preparation may lead to some abnormalities not being seen.
All measurements made by ultrasound are approximate and depends on machine, operator, patient preparation, etc -Hence too much reliance should not be placed on exact measurements-for example stones may appear larger or smaller depending on the position.
Some abnormalities like bowel problems may be seen intermittently-if other bowel covers the lesion, it may not be visualized at that particular time and may become visible after some time. Some abnormalities like appendicitis cannot always be diagnosed by ultrasound alone and your Doctor may ask for other tests or repeat the scans.
Some problems like ureteric stones may not be visualized especially in mid third portion of ureter. Stones can change position over a period of time and become visible on a later scan.
Some problems like abscess may not be seen if scan is done early in its course- it changes over a period of time and becomes visible later and its appearance also varies with time.
Ovaries and cysts can change position over a period of time as they are mobile structures. Left and right mentioned in the report would be position seen at the time of scan and may change later.
Diagnosis mentioned are the most likely cause of problem to help your Doctor to get correct idea as to what to do next. There is almost always other possibilities which are less likely-your Dr is aware of this and will contact us in case of any doubts.
Some problems like ectopic pregnancies may not be seen in the early stage and many times become visible hours or days later. Hence repeat scans are asked for many times, this does not mean that the previous scan was wrong or not done properly.
Ultrasound can image many problems, however cause cannot be detected and treatment cannot be based only on images. Hence, please consult your Dr regarding these things.
While explaining technical things in non-technical language, each person uses different words to explain the same thing-hence if you consult different doctors, you may get varying explanation which is a common source of confusion. Any explanation may not correspond exactly to what your Dr explains-this leads to a common problem - different doctors tell different things.
Correlation with blood tests and other scans are required in many problems/conditions.

Proper history with all details of present and previous pregnancies/children with problem should be furnished. This will help us in providing specialized evaluation. Without the previous scan and lab reports the current study may not be able to provide complete information.
In mid trimester anomaly scan that is 18-20 weeks as per ISUOG guidelines, only the fetal parts mentioned in the scan report have been evaluated. Parts of fetus not mentioned in the report are not evaluated in routine scan. For example counting fingers/toes, assessment of external ears, palate etc.
TIFFA scan: Even with a very detailed ultrasound study, all abnormalities cannot be excluded-even if all available tests in the world are done, it is not possible to say with certainly that a given fetus is completely normal-this is because there are many rare conditions for which there are no tests available and few other abnormalities evolve over time.
Certain anomalies like delayed sulcation of the brain can be diagnosed only after 24-25 weeks of gestation, and hence in certain cases repeat anomaly scan may be advised.
Some anomalies like soft tissue fusion of fingers/toes, absence of anal opening or absence of auditory opening may not be recognizable by ultrasonography.
Third trimester (28 weeks after) ultrasound scan is basically for growth assessment and fetal well-being. It is not possible to do a detailed structural anomaly scan at this time.
Late onset/evolving anomalies like congenital diaphragmatic hernia/hydrocephalous/microcephaly/clubfoot/certain heart abnormalities/kidney and intestinal obstructive anomalies etc, may not be picked up in mid trimester scan.
Study of genital organs is prohibited under the PCPNDT ACT. Hence detection of abnormalities of the genital organs is not feasible.
Despite a protocol driven, detailed study, some anomalies can be missed in prenatal ultrasound scan. Under some circumstances a normal ultrasound finding may be misinterpreted as an anomaly. These are due to limitations of ultrasound/fetal position.
Some findings may not be anomalies but may necessitate serial USG follow-up, biochemical testing, invasive testing example: Thick nuchal translucency, and delayed or absent nasal bone formation, fluid in kidney/excess fluid in brain cavities etc. These findings may be transient and may change with time.
Specialized fetal echocardiogram or extended neurosonography will be done only if the referred Dr requests for the same or if the basic anomaly scan warrants the same. It should noted that even though the brain may looked normal on ultrasound examination, its function cannot be evaluated.
Even with the detailed fetal echocardiogram with the latest equipment by an experienced operator, many problems go undetected due to a variety of factors like obesity of mother, small size of heart, fetal heart rate being double that of adult heart rate normally, inability to position fetus as per requirement etc. Even in a specialized fetal echocardiography, certain cardiac anomalies such as secundum ASD, small VSD, PDA and other subtle anomalies cannot be picked up.
Several factors like gestational age at which scan is done, fetal position at the time of scan, maternal body habitus, liquor volume and shadows from fetal parts may restrict/limits visibility. The report may Carry this information. The study may then necessitate repeat scans. Review scans for under filled stomach/bladder or for position change of fetus to enable assessment of face/heart/spine may be needed. It becomes the patient’s responsibility to come for the necessary reviews and within the time mentioned.
Obesity of the pregnant lady is a special challenge for ultrasonography. The fat in the mother’s abdominal wall absorbs the ultrasound energy, thus degrading the images and making the diagnosis of normality or abnormality very difficult.
Chromosomal anomalies cannot be diagnosed on ultrasound scans alone. Ultrasound Markers, if noted will only increase the risk of fetus having chromosomal abnormalities and will warrant further evaluation. Karyotyping (chromosomal study of the fetus by invasive testing with needle) is the confirmatory test. Such a needle/invasive test will carry a risk of procedure related pregnancy loss which will be discussed when necessary by the Dr. 3-D and 4D ultrasound is used only to assess certain abnormalities and not as a routine.
Multiple gestations (twins/triplets) may cause difficulties in the ultrasound examination due to fetal position and overlap.
Growth and development are 2 different things-growth is increase in size, development is different parts forming. There can be abnormality in one may occur without affecting the other.

Doppler is only a screening test for problems in the arteries and accuracy is lower-however, it is cost effective and easily available, hence is done first. Other testing may be required to confirm Doppler findings. Some problems like DVT may evolve and change over time and hence repeat scans may be necessary.

Ultrasound is a screening test and in some cases other tests will be required to find out cause of ultrasound changes.
Some problems like torsion of testis can spontaneously resolved and a later date occur again(called torsion detorsion sequence), hence findings depend on what is there at the time of scan and cannot predict future changes.
Some problems evolves, for example severe infection can lead to cutting off blood supply to testes and behave like torsion even though there is no torsion on earlier scan.
This is just an attempt to explain the limitations of ultrasound with a few common examples and is not a comprehensive document. In case of any doubts, please contact your Dr. Relevant points regarding the case and further requirements/investigations, will be explained to patient in the local language.