Ultrasound-Why,When,What is Found

8/8/2019 Ultrasound-Why,When,What is Found

1/14

Ultrasound-Why, When, What is found?

Question

What are the parameters for ultrasound exams in pregnant women? A patient has requested an

ultrasound exam at each prenatal visit on the basis that a friend in Europe had one done at everyprenatal visit.

Response From Expert

Karen L. Koscica, DODepartment of Obstetrics & Gynecology and Women's Health, Albert Einstein College of

Medicine/Montefiore Medical Center, Bronx, New York

Peter Bernstein, MD, MPHAssociate Professor of Clinical Obstetrics & Gynecology and Women's Health, Albert Einstein

College of Medicine/Montefiore Medical Center, and Medical Director, Obstetrics andGynecology, Comprehensive Family Care Center of Montefiore Medical Group, Bronx, NewYork

The question of the frequency of ultrasound examinations in pregnancy has been debated at

length. There are many indications for sonography during pregnancy, but routine screeningremains controversial. Routine screening implies that the procedure is performed in a low-risk

population, or in those without a specific clinical indication, in order to detect potentialproblems. In pregnancy, the reason most often cited for routine ultrasound is to detect fetal

anomalies, and this ultrasound examination is normally performed at approximately 18-20 weeksgestational age.

There have been several trials of routine ultrasound examinations during pregnancy. The largest,a prospective, randomized one of routine vs indicated ultrasound examinations, was the RADIUS

study.[1]

This study included 15,530 pregnant women. One group underwent routine ultrasoundat 15-22 weeks and again at 31-35 weeks. The other group underwent ultrasound only if a

specific indication arose, such as uncertain dating or positive triple screen. The primary outcomemeasure was adverse perinatal outcome (fetal or neonatal death or moderate or severe neonatal

morbidity). The secondary outcomes were multiple gestations, birthweight, and incidence ofpreterm delivery.

[1]

This trial found no difference in perinatal outcome between the groups. There was, however, a 3-

fold increase in the detection of fetal anomalies, which did not have an effect on perinataloutcome, the investigators' primary outcome variable. Therefore, they concluded that, "The


2/14

adoption of routine ultrasound screening in the United States would add considerably to the costof care in pregnancy, with no improvement in perinatal outcome."

[1]

A critical analysis of the study reveals that the patients were primarily low-risk patients being

seen in private offices. In reality, 60% of the potential population was excluded for high-risk

conditions for which ultrasound examinations were deemed necessary, and then 45% of thecontrol population subsequently developed an indication for an ultrasound examination. Thus,the vast majority of patients underwent ultrasound. Of significant concern is that only 17% of

fetal anomalies were detected with ultrasound. This raises a question of quality of the ultrasoundexaminations being performed.[2,3] Additionally, any cost/benefit analysis needs to include the

cost of care of infants with birth defects and the expenses saved if pregnant women choose toterminate a pregnancy with a significant anomaly. The cost of routine screening may be less than

the cost of support for newborns with major anomalies.[3]

The main indications for routine ultrasound are to detect fetal anomalies, confirm pregnancydating, and diagnose multiple gestations. Studies are still needed to demonstrate the cost-

effectiveness of this intervention. The advantages must be weighed against the false positivesand false negatives of the test. Although ultrasound has become standard of care in many

settings, the routine use of this test is not universally accepted.

Mike Wlydes, Perinatal Institute

This area of the site is designed to inform pregnant women about ultrasound scanning in

pregnancy. I am a consultant obstetrician & gynaecologist with an interest and background inobstetric ultrasound. I have been a consultant in a large maternity hospital in Birmingham UK

since 1994. I have tried within the text to give an account of my experiences, which I hope areshared by the majority of people undertaking ultrasound scans in pregnancy.

The text is divided into the different types of scans undertaken at different times duringpregnancy.

Early pregnancy assessment scans

These scans are done following a problem, usually either vaginal bleeding or abdominal pain.

These symptoms are often the first signs of miscarriage or sometimes ectopic pregnancy, and theultrasound scan is very helpful in distinguishing between different situations.

Scanning can be done in 2 ways in early pregnancy. Firstly an abdominal scan, where thewoman is asked to fill up her bladder as much as possible, and gel is applied to the maternal

abdomen to achieve images of the pelvic organs. Often this is helpful but frequently theincreased image quality of a vaginal scan is required to make the diagnosis. A vaginal scan

involves a specialy designed ultrasound probe being placed within the vagina to look at theuterus and ovaries more closely. The scan doesnt hurt, and it cannot cause any damage or injury

to the pregnancy.


3/14

The common outcomes from an early pregnancy assessment scan are:

1. Normal on-going intra-uterine pregnancy. More than 90% of pregnancies seen to have afetal heart beat present on ultrasound will end with a healthy baby. A few will still

miscarry, but there is no proven benefit to bed rest or other interventions. The best

advice is to do what feels right, but many women will wish to continue with normalactivities, although vigorous physical exercise may be best avoided until bleeding hassettled.

2. A miscarriage. If a woman is more than 6 or 7 weeks pregnant it is usually possible tosee a normal pregnancy within the uterus using vaginal ultrasound. Ultrasound scanning

can sometimes be certain that a pregnancy has miscarried, and sometimes the situation isunclear. If there is any doubt then further scanning 2 weeks later will give a normal

pregnancy a chance to declare itself.3. Ectopic pregnancy. A pregnancy outside the uterus, usually in the fallopian tube can

make the pregnancy woman ill, sometimes very ill. Ectopic pregnancies can mimicmiscarriage with vaginal bleeding, they may case abdominal pain or they may give no

symptoms. If a pregnancy is advanced past 6 weeks and the pregnancy test is positive,and the uterus looks empty on ultrasound scan then an ectopic pregnancy is possible. It

may be necessary in some cases to undertake an operation called a laparoscopy to inspectthe tubes directly if an ectopic pregnancy is suspected.

The 11 to 13 week scan

This scan has been developed over the last 5 to 10 years to screen for fetal anomalies in normalpregnancies. The first part of the scan assessment is a general look around the structures of the

baby, the arms and legs, hands and feet, heart, stomach, bladder and head are usually visible.Movements are seen and the position and texture of the placenta. The second part of the scan is

to measure nuchal translucency (NT). NT is fluid in the skin at the back of the fetal neck. Allfetuses have some nuchal fluid, but some have more than others. It has been found from

studying thousands of cases that the measurement of NT can give a risk for Downs syndrome.Recently the addition of a first trimester blood test has made screening for trisomy 21 more

accurate. Using both the blood test and the nuchal translucency scan together it is possible toidentify 85% of cases of Downs syndrome. Nuchal translucency scanning is currently not

available widely within the National Health Service. Further information on having a nuchal testis available from www.nuchal.info.

A Dating scan

A dating scan aims to make measurements which accurately predict the due date of the baby.

This can be done from 8 to 20 weeks, but the test is probably more accurate before 14 weeksthan afterwards. The dating scan does not aim to assess fetal anomalies, and can be completedfairly quickly. Dating scans can be done using relatively unsophisticated ultrasound equipment,

sometimes these scans can be done in GP surgeries, or other community settings.

Mid pregnancy anomaly scanning


4/14

The most common time to do a fetal anomaly scan has been 20 weeks (between 18 and 22weeks). The purpose of scanning can be considered under a number of headings:

Confirming everything is OK

Most scans show a normal baby, and having this reassurance is what most women want fromtheir scan. However scanning cannot pick up all problems and you should be aware that abouthalf of significant problems cannot be identified with a scan.

Diagnosing serious fetal anomalies

The person undertaking your scan will be going through a mental checklist of normal and

abnormal findings. Many of the problems that are diagnosed during pregnancy are serious, and

in many cases the only option to consider is whether to have a termination of the pregnancy, orcontinue the pregnancy. Many pregnant women at 20 weeks would not consider a termination of

the pregnancy, and for these people having a scan should be considered carefully, and possibly to

enjoy the pregnancy until the problem comes to light.

Minor problems and variations of normal

It is quite common for minor problems to be suspected on ultrasound scanning which have littleor no impact on the health of a child. Being told there is a problem on scanning is always

stressful, and even with reassurance the anxiety levels for the rest of the pregnancy areincreased. Some things which are seen on scanning increase the risks of Downs syndrome, and

it may be that the result of the scan is a discussion with you about having additional tests done(such as amniocentesis). Scan findings which increase the risk of Downs syndrome are called

markers.

To get a picture and tell the sex of the baby

These objectives seem to be quite common amongst pregnant women, but neither are especially

important from the sonographers point of view. It is often possible to tell the sex of baby at 20

weeks, at least 70%, but this will only be correct 95% of the time. Many sonographers find theissue of fetal sexing difficult, it seems to demonstrate that the woman involved does not

understand the purpose of the scan, and in some extreme cases women have been reported tohave undergone termination of pregnancy based on the wrong sex being found. Many

departments operate a policy of not telling women the sex of their baby, even if it is known, butmost units are happy to tell women the sex of their unborn child if it does not prolong the

examination and the couple are able to cope with the news. These decisions are partly a matterof policy, but also of individual judgement of the professionals involved in providing the

scanning service.

Other findings on a 20 week scan

The position of the placenta can be diagnosed on ultrasound


5/14

About 20% of placentas at 20 weeks have some element within the lower segment of the uterus.1% will ultimately end up being a problem requiring caesarean section (placental praevia).

Many centres have abandoned repeating ultrasound examination for these cases, but incircumstances where the placenta seems to be entirely within the lower uterus, and potentially

blocking the way out for the baby it may be best to reassess in late pregnancy.

Growth Scans

Sometimes it is thought necessary to follow the growth of a baby during pregnancy. This is

usually undertaken from 28 weeks onwards, and the scan measures the abdominal circumference

and head circumference to assess the babys size. These scans can also look at the amount ofliquor (amniotic fluid) around the baby, and assess the blood flow through the placenta or within

the baby. These additional tests are often important in trying to decide whether there is aproblem with the baby, rather than just measuring. There is no benefit to routine scanning in the

last 3 months of pregnancy, but for complex pregnancies, such as twins it can be helpful.

Advice for mothers to be

As you decide whether to have an ultrasound scan you need to consider the good, and the bad

that might come from it. Most scans are normal, and that is reassuring, but if your baby has amajor problem then the scan might allow you to consider a termination of the pregnancy, but this

would always be your choice, even if the problems are so serious that the baby cant survive. Ifminor problems are identified you risk being very worried, and maybe having additional tests

done, when everything is perfectly normal. The information on these pages helps to define therisks of particular problems being present, or being diagnosed on scan. The issue of whether you

should have a scan is an individual issue for you to consider.

What are Obstetric Ultrasound Scans?

Obstetric Ultrasound is the use of ultrasound scans inpregnancy. Since its introduction in the late 1950sultrasonography has become a very useful diagnostic tool inObstetrics.

Currently used equipments are known as real-timescanners, with which a continous picture of the movingfetus can be depicted on a monitor screen. Very highfrequency sound waves of between 3.5 to 7.0 megahertz(i.e. 3.5 to 7 million cycles per second) are generally used

for this purpose.

They are emitted from a transducer which is placed in contact with the maternal abdomen,and is moved to "look at" (likened to a light shined from a torch) any particular content ofthe uterus. Repetitive arrays of ultrasound beams scan the fetus in thin slices and arereflected back onto the same transducer.


6/14

The information obtained from different reflections arerecomposed back into a picture on the monitor screen (asonogram, or ultrasonogram). Movements such as fetal heartbeat and malformations in the feus can be assessed andmeasurements can be made accurately on the imagesdisplayed on the screen. Such measurements form the

cornerstone in the assessment of gestational age, size andgrowth in the fetus.

Afull bladder is often required for the procedure whenabdominal scanning is done in early pregnency. There may be some discomfort frompressure on the full bladder. The conducting gel is non-staining but may feel slightly coldand wet. There is no sensation at all from the ultrasound waves.

A short history of the development of ultrasound in pregnancy can be found in the Historypages.

Why and when is Ultrasound used in Pregnancy?

Ultrasound scan is currently considered to be a safe, non-invasive, accurate and cost-effective investigation in the fetus. It has progressively become an indispensible obstetrictool and plays an important role in the care of every pregnant woman.

The main use of ultrasonography are in the following areas:

1. Diagnosis and confirmation ofearly pregnancy.

The gestational sac can be visualized as early as four and ahalf weeks of gestation and the yolk sac at about five weeks.The embryo can be observed and measured by about five anda half weeks. Ultrasound can also very importantly confirm thesite of the pregnancy is within the cavity of the uterus.

2. Vaginal bleeding in early pregnancy.

The viability of the fetus can be documented in the presence ofvaginal bleeding in earlypregnancy. A visible heartbeat could be seen and detectable by pulsed doppler ultrasoundby about 6 weeks and is usually clearly depictable by 7 weeks. If this is observed, theprobability of a continued pregnancy is better than 95 percent. Missed abortions andblighted ovum will usually give typical pictures of a deformed gestational sac and absence offetal poles or heart beat.


7/14

Fetal heart rate tends to vary with gestational age in the very early parts of pregnancy.Normal heart rate at 6 weeks is around 90-110 beats per minute (bpm) and at 9 weeks is140-170 bpm. At 5-8 weeks a bradycardia (less than 90 bpm) is associated with a high riskof miscarriage.

Many women do not ovulate at around day 14, so findings

after a single scan should always be interpreted with caution.The diagnosis of missed abortion is usually made by serialultrasound scans demonstrating lack of gestationaldevelopment. For example, if ultrasound scan demonstrates a7mm embryo but cannot demonstrable a clearcut heartbeat, amissed abortion may be diagnosed. In such cases, it isreasonable to repeat the ultrasound scan in 7-10 days toavoid any error.

The timing of a positive pregnancy test may also be helpful inthis regard to assess the possible dates of conception. A positive pregnancy test 3 weekspreviously for example, would indicate a gestational age of at least 7 weeks. Such

information would be useful against the interpretation of the scans. Please read the FAQsfor more comments.

In the presence of first trimester bleeding, ultrasonography is also indispensible in the earlydiagnosis ofectopic pregnancies and molar pregnancies.

3. Determination ofgestational age and assessment offetal size.

Fetal body measurements reflect the gestational age of the fetus. This is particularly true inearly gestation. In patients with uncertain last menstrual periods, such measurements mustbe made as early as possible in pregnancy to arrive at a correct dating for the patient. SeeFAQ. In the latter part of pregnancy measuring body parameters will allow assessment ofthe size and growth of the fetus and will greatly assist in the diagnosis and management ofintrauterine growth retardation (IUGR).

The following measurements are usually made:

a) The Crown-rump length (CRL)This measurement can be made between 7 to 13 weeksand gives very accurate estimation of the gestationalage. Dating with the CRL can be within 3-4 days of thelast menstrual period. (Table) An important point tonote is that when the due date has been set by anaccurately measured CRL, it should not be changed by asubsequent scan. For example, if another scan done 6or 8 weeks later says that one should have a new duedate which is further away, one should not normallychange the date but should rather interpret the finding as that the baby is notgrowing at the expected rate.

b) The Biparietal diameter (BPD)


8/14

The diameter between the 2 sides of the head. This is measured after 13 weeks. Itincreases from about 2.4 cm at 13 weeks to about 9.5 cm at term. Different babiesof the same weight can have different head size, therefore dating in the later part ofpregnancy is generally considered unreliable. (Chart and further comments) Datingusing the BPD should be done as early as is feasible.

c) The Femur length (FL)Measures the longest bone in the body and reflects the longitudinal growth of thefetus. Its usefulness is similar to the BPD. It increases from about 1.5 cm at 14weeks to about 7.8 cm at term. (Chart and further comments) Similar to the BPD,dating using the FL should be done as early as is feasible.

d) The Abdominal circumference (AC)

The single most important measurement to make in late pregnancy. It reflects moreof fetal size and weight rather than age. Serial measurements are useful inmonitoring growth of the fetus. (Chart and further comments) AC measurements

should not be used for dating a fetus.

Other important measurements are discussed here.

The weight of the fetus at any gestation can also beestimated with great accuracy using polynomial equationscontaining the BPD,FL, and AC. computer softwares andlookup charts are readily available. For example, a BPD of 9.0cm and an AC of 30.0 cm will give a weight estimate of 2.85kg. (comments)

4. Diagnosis offetal malformation.

Many structural abnormalities in the fetus canbe reliably diagnosed by an ultrasound scan, and these can usually be madebefore 20 weeks. Common examples include hydrocephalus,anencephaly,myelomeningocoele,achondroplasia and other dwarfism,spina bifida,exomphalos,Gastroschisis,duodenal atresia and fetal hydrops. With morerecent equipment, conditions such as cleft lips/ palate and congenital cardiacabnormalities are more readily diagnosed and at an earlier gestational age.(Also see the FAQ and Anomalies pages).

First trimester ultrasonic 'soft' markers for chromosomal abnormalities suchas the absence offetal nasal bone, an increased fetal nuchal translucency(the area at the back of the neck) are now in common use to enabledetection ofDown syndrome fetuses.

Read also: Soft Markers - A Guide for Professionals and Ultrasonographic "soft markers" offetal chromosomal defects.


9/14

Ultrasound can also assist in other diagnostic procedures inprenatal diagnosis such as amniocentesis,chorionic villussampling,cordocentesis (percutaneous umbilical blood sampling)and in fetal therapy.

5. Placental localization.

Ultrasonography has become indispensible in thelocalization of the site of the placenta and determining itslower edges, thus making a diagnosis or an exclusion ofplacenta previa. Other placental abnormalities inconditions such as diabetes,fetal hydrops,Rhisoimmunization and severe intrauterine growthretardation can also be assessed.

. Multiple pregnancies.

In this situation, ultrasonography is invaluable indetermining the number of fetuses, the chorionicity, fetal presentations, evidence of growthretardation and fetal anomaly, the presence of placenta previa, and any suggestion oftwin-to-twin transfusion.

7.Hydramnios and Oligohydramnios.

Excessive or decreased amount of liquor (amniotic fluid) can be clearly depicted byultrasound. Both of these conditions can have adverse effects on the fetus. In both these

situations, careful ultrasound examination should be made to exclude intraulterine growthretardation and congenital malformation in the fetus such as intestinal atresia,hydropsfetalis or renal dysplasia. See also FAQ and comments.

8. Other areas.

Ultrasonography is of great value in other obstetric conditions such as:

a) confirmation of intrauterine death.

b) confirmation of fetal presentation in uncertain cases.

c) evaluating fetal movements, tone and breathing in the Biophysical Profile.

d) diagnosis of uterine and pelvic abnormalities during pregnancy e.g. fibromyomataand ovarian cyst.


10/14

Transvaginal Scans

With specially designed probes, ultrasound scanning can be

done with the probe placed in the vagina of the patient. This

method usually provides better images (and therefore more

information) in patients who are obese and/ or in the early

stages of pregnancy. The better images are the result of the

scanhead's closer proximity to the uterus and the higher

frequency used in the transducer array resulting in higher

resolving power. Fetal cardiac pulsation can be clearly observed as early as 6 weeks of

gestation.

Vaginal scans are also becoming indispensible in the early diagnosis ofectopic pregnancies.An increasing number of fetal abnormalities are also being diagnosed in the first trimesterusing the vaginal scan. Transvaginal scans are also useful in the second trimester in thediagnosis of congenital anomalies. Read one of my presentations at OBGYN.net-Ultrasound.

Doppler Ultrasound

The doppler shift principle has been used for a long time in

fetal heart rate detectors. Further developments in doppler

ultrasound technology in recent years have enabled a great

expansion in its application in Obstetrics, particularly in the

area of assessing and monitoring the well-being of the

fetus, its progression in the face of intrauterine growth

restriction, and the diagnosis of cardiac malformations.Doppler ultrasound is presently most widely employed inthe detection of fetal cardiac pulsations and pulsations inthe various fetal blood vessels. The "Doptone" fetal pulse detector is a commonly used

handheld device to detect fetal heartbeat using the same dopplerprinciple.

Blood flow characteristics in the fetal blood vessels can beassessed with Doppler 'flow velocity waveforms'. Diminishedflow, particularly in the diastolic phase of a pulse cycle isassociated with compromise in the fetus. Various ratios of thesystolic to diastolic flow are used as a measure of this

compromise. The blood vessels commonly interrogated includethe umbilical artery, the aorta, the middle cerebral arteries, theuterine arcuate arteries, and the inferior vena cava.

The use ofcolor flow mapping can clearly depict the flow ofblood in fetal blood vessels in a realtime scan, the direction of

the flow being represented by different colors. Color doppler is particularly indispensible inthe diagnosis offetal cardiac and blood vessel defects, and in the assessment of thehemodynamic responses to fetal hypoxia and anemia.


11/14

A more recent development is the Power Doppler (Doppler angiography). It uses amplitudeinformation from doppler signals rather than flow velocity information to visualize slow flowin smaller blood vessels. A color perfusion-like display of a particular organ such as theplacenta overlapping on the 2-D image can be very nicely depicted. Doppler examinationscan be performed abdominally and via the transvaginal route. The power emitted by adoppler device is greater than that used in a conventional 2-D scan. Its use in early

pregnancy is therefore cautioned.

Doppler facilities are generally an integral part of modern ultrasound scanners. They merelywould need to be switched on to function. One does not need to 'go' to another machine forthe doppler investigations.

3-D and 4-D Ultrasound

3-D ultrasound can furnish us with a 3 dimensional image of what we are

scanning. The transducer takes a series of images, thin slices, of the subject,

and the computer processes these images and presents them as a 3 dimensional

image. Using computer controls, the operator can obtain views that might not be available

using ordinary 2-D ultrasound scan. 3-dimensional ultrasound is quickly moving out of the

research and development stages and is now widely employed in a clinical setting. It too, is

very much in the News. Faster and more advanced commercial models are coming into the

market. The scans requires special probes and software to accumulate and render the

images, and the rendering time has been reduced from minutes to fractions of a seconds.

A good 3-D image is often very impressive to the parents. Further 2-D scans may beextracted from 3-D blocks of scanned information. Volumetric measurements are moreaccurate and both doctors and parents can better appreciate a certain abnormality or the

absence of a certain abnormality in a 3-D scan than a 2-D one and there is the possibility ofincreasing psychological bonding between the parents and the baby.

An increasing volume of literature is accumulating on the usefulness of3-D scans and the diagnosis of congenital anomalies could receiverevived attention. Present evidence has already suggested that smallerdefects such as spina bifida,cleft lips/palate, and polydactyl may bemore lucidly demonstrated. Other more subtle features such as low-setears, facial dysmorphia or clubbing of feet can be better assessed,leading to more effective diagnosis of chromosomal abnormalities. Thestudy of fetal cardiac malformations is also receiving attention. Theability to obtain a good 3-D picture is nevertheless still very much

dependent on operator skill, the amount of liquor (amniotic fluid)around the fetus, its position and the degree of maternal obesity, sothat a good image is not always readily obtainable.

More recently,4-D or dynamic 3-D scanners are in themarket and the attraction of being able to look at the face andmovements of your baby before birth was also enthusiasticallyreported in parenting and health magazines. This is thought tohave an important catalytic effect for mothers to bond to their


12/14

babies before birth. What are known as 're-assurance scans' and the rather misnamed'entertainment scans' have quickly become popular.

Most experts do not consider that 3-D and 4-D ultrasound will be a mandatory evolution ofour conventional 2-D scans, rather it is an additional piece of tool like doppler ultrasound.Most diagnosis will still be made with the 2-D scans. 3-D ultrasound appears to have great

potential in research and in the study offetal embryology. Whether 3-D ultrasound willprovide unique information or merely supplemental information to the conventional 2-Dscans will remain to be seen.

Click here for some good sample images courtesy ofDr. Bernard Benoit. Visit the GE4D site for more pictures and information. Dr. Najeeb Layyous's 3-D and 4-D website alsohas many more pictures and clips. Read also the FAQ page.

A short history of the development of 3-D ultrasound in pregnancy can be found in theHistory pages.

The Schedule

There is no hard and fast rule as to the number of scans a woman

should have during her pregnancy. A scan is ordered when an

abnormality is suspected on clinical grounds. Otherwise a scan is

generally booked at about 7 weeks to confirm pregnancy,

exclude ectopic or molar pregnancies,confirm cardiac pulsation andmeasure the crown-rump length for dating.A second scan is performed at 18 to 20 weeks mainly to look for congenitalmalformations, when the fetus is large enough for an accurate survey of the fetalanatomy. multiple pregnancies can be firmly diagnosed and dates and growth can alsobe assessed. Placental position is also determined. Further scans may be necessary ifabnormalities are suspected.

Many centers are now performing an earlier screening scan at around 11-14 weeks tomeasure the fetal nuchal translucency and to evaluate the fetal nasal bone (and morerecently, to detect tricuspid regurgitation) to aid in the diagnosis ofDown Syndrome. Some

centers will do blood test biochemical screening at the same visit.

Further scans may sometimes be done at around 32 weeks or later to evaluate fetal size(to estimate the fetal weight) and assess fetal growth. Or to follow up on possibleabnormalities seen at an earlier scan. Placental position is further verified. The mostcommon reason for having more scans in the later part of pregnancy is fetal growthretardation. Doppler scans may also be necessary in that situation.


13/14

The total number of scans will vary depending on whether aprevious scan has detected certain abnormalities that requirefollow-up assessment. What is often referred to as a Level IIscan merely indicates a "targeted" examination where it isdone when an indication is present or when an abnormality issuspected in a previous examination. In fact professional

bodies such as the American Institute of Ultrasound in Medicinedoes not endorse or encourage the use of these terms. A more"thorough" examination is usually done at an a perinatal centeror specialised clinic where more expertise and betterequipments may be present.

One should not dwell too much on the definitions or guidelines for a level II ultrasound scan.The prenatal sonologist should always try very hard to look for and assess any abnormalitythat may be present in the fetus. It is not very meaningful to be talking about level III oreven level IV scans.

That a pregnancy should be scanned at 18 to 20 weeks as a rule is gradually becoming a

matter of routine practice. Please go to the FAQ page andN

ews page for other discussions.A rather thorough discussion paper on Ultrasound screening in pregnancy can be foundhere. Read also the RCOG's paper on routine screening in pregnancy.

What about Safety?

It has been over 40 years since ultrasound was first used on

pregnant women. Unlike X-rays, ionizing irradiation is not present

and embryotoxic effects associated with such irradiation should not

be relevant. The use of high intensity ultrasound is associated with

the effects of "cavitation" and "heating" which can be present with

prolonged insonation in laboratory situations.

Although certain harmful effects in cells are observed in a laboratorysetting, abnormalities in embryos and offsprings of animals and humans have not beenunequivocally demonstrated in the large amount ofstudies that have so far appeared inthe medical literature purporting to the use of diagnostic ultrasound in the clinical setting.

Apparent ill-effects such as low birthweight, speech and hearing problems, brain damageand non-right-handedness reported in small studies have not been confirmed orsubstantiated in larger studies from Europe. The complexity of some of the studies havemade the observations difficult to interpret. Every now and then ill effects of ultrasound onthe fetus appears as a news item in papers and magazines. Continuous vigilance isnecessary particularly in areas of concern such as the use of pulsed Doppler in the firsttrimester.


14/14

The greatest risks arising from the use of ultrasound are the possible over- and under-diagnosis brought about by inadequately trained staff, often working in relative isolation andusing poor equipment.

A discussion on the various possible effects of ultrasound on the human fetus can be foundhere. Ultrasound scans should best be performed when there is a clear indication to do so.

When there is, safety considerations should not be an issue to prevent its prudent use.

It should be bornt in mind that prenatal ultrasound cannot diagnose allmalformations and problems of an unborn baby (reported figures range from 40to 98 percent), so one should never interpret a normal scan report as aguarantee that the baby will be completely normal. Some abnormalities are very

difficult to find or to be absolutely certain about.

Some conditions, like for example hydrocephalus, may not have been obvious at the time ofthe earlier scan. The position of the baby in the uterus has a great deal to do with how well

one sees certain organs such as the heart, face and spine. Sometimes a repeat examinationhas to be scheduled the following day, in the hopes the baby has moved.

Images tend also to be strikingly clear in skinny patients with lots of amniotic fluid, andfrustratingly fuzzy in obese women, particularly if there is not much amniotic fluid as incases of growth restriction. As in almost every endeavor, there is also a wide difference inthe skill, training, talent, and interest of the sonographer or sonologists. The improvementsin equipment has also lead to the earlier detection of abnormal structures in the fetusbringing along with it "false positives" and "difficult-to-be-sure-what-will-happen" diagnosisthat could generate huge amount of undue anxiety in patients.

According to Anne Frye, midwife and author of "Understanding Lab Work in the Childbearing

Year" (4th Ed.)p. 405:

Doppler Devices: Many women do not realize that doppler fetoscopes are ultrasound devices.(apparently, neither do many care providers. Time after time, women are assured by doctors and

even some nurse midwives that a doppler is not an ultrasound device.) . . . .

Not well publicized for obvious reasons, doppler devices expose the fetus to more powerfulultrasound than real time (imaging) ultrasound exams. One minute of doppler exposure is equal

to 35 minutes of real time ultrasound. This is an important point for women to consider whendeciding between an ultrasound exam and listening with a doppler to determine viability in early

pregnancy. . . . .

If you have a doppler, put it aside and make a concerted effort to learn to listen yourself! Save

your doppler for those rare occasions when you cannot hear the heart rate late into pushing or tofurther investigate suspected fetal death. " copyright l990, Anne Frye, B.H. Holistic Midwifery.

Ultrasound-Why,When,What is Found

Documents