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Obstetric Ultrasound Scans

Pemeriksaan ultrasonografi, pertama dimanfaatkan dalam ilmu

kebidanan pada tahun 1954.

Gelombang suara dipancarkan dengantransduceryang diletakanpada bagian abdomen ibu hamil, dan di gerakan untuk melihatbagian uterus yang diperiksa. Pancaran gelombang ultrasoundmemantulkan cahaya balik bergantung dengan densitas jaringanterdapat pada fetus. The information obtained from differentreflections are recomposed back into a picture on the monitorscreen (a sonogram, or ultrasonogram). Movements such as fetalheart beat and malformations in the feus can be assessed andmeasurements can be made accurately on the images displayed onthe screen. Such measurements form the cornerstone in theassessment of gestational age, size and growth in the fetus.

A full bladder is often required for the procedure whenabdominal scanning is done in early pregnency. There may besome discomfort from pressure on the full bladder. The

conducting gel is non-staining but may feel slightly cold and wet.There is no sensation at all from the ultrasound waves.

Ultrasound scan adalah pemeriksaan yang tidak terdapat resikotinggi, tidak-invasive, akurat and murah.

1. Diagnosis dan deteksi kehamilan dini.

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Gestational sac dapat terlihat semudah empat setengah minggudari usia kehamilan. Yolk sac dapat terlihat dalam waktu limaminggu. Embryo dapat diobservasi dan di ukur setelah limasetengah minggu. Ultrasound menjadi sarana yang penting untuk

menentukan lokasi kehamilan dalam uterus.

2. Vaginal bleeding in early pregnancy.The viability of the fetus can be documented in the presence ofvaginal bleeding in early pregnancy. A visible heartbeat could beseen and detectable by pulsed doppler ultrasound by about 6weeks and is usually clearly depictable by 7 weeks. If this isobserved, the probability of a continued pregnancy is better than

95 percent. Missed abortions andblighted ovumwill usually givetypical pictures of a deformed gestational sac and absence of fetalpolesor heart beat.

Fetal heart rate tends tovary with gestational agein the very earlyparts of pregnancy. Normal heart rate at 6 weeks is around 90-110beats per minute (bpm) and at 9 weeks is 140-170 bpm. At 5-8weeks a bradycardia (less than 90 bpm) is associated with a highrisk of miscarriage.

Many women do not ovulate at around day 14, so findings after asingle scan should always be interpreted with caution. Thediagnosis of missed abortion is usually made by serial ultrasoundscans demonstrating lack of gestational development. Forexample, if ultrasound scan demonstrates a 7mm embryo butcannot demonstrable a clearcut heartbeat, a missed abortion maybe diagnosed. In such cases, it is reasonable to repeat theultrasound scan in 7-10 days to avoid any error.

The timing of a positive pregnancy test may also be helpful in this

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regard to assess the possible dates of conception. A positivepregnancy test 3 weeks previously for example, would indicate agestational age of at least 7 weeks. Such information would beuseful against the interpretation of the scans. Please read theFAQs

for more comments.

In the presence of first trimester bleeding, ultrasonography is alsoindispensible in the early diagnosis of ectopic pregnancies andmolar pregnancies.

3. Determination of gestational age and assessment of fetalsize.

Pengukuran badan fetus menandai usia fetus. Pada ibu hamildengan riwayat haid tidak teratur menjadi pemeriksaan yangdiutamakan dengan kepentingan untuk mengetahui usiakehamilan. Dengan mengetahui ukuran dan perkembangan fetuskita dapat mengetahui jika fetus dapat didiagnosis intrauterinegrowth restriction (IUGR) atau tidak.

The following measurements are usually made:

a) The Crown-rump length (CRL) pengukuran CRL dapat di

lakukan 7 sampai 13. Dating with the CRL can be within 3-4days of the last menstrual period. Jika pengukuran CRLdilakukan lagi 6-8 minggu setelah scan pertama akan terlihatseakan-akan fetus tidak bertumbuh sesuai usia. Maka itu

timframe antara 7-13 minggu adalah patokan yang paling

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optimal. Dalam pemeriksaan CRL itu dimulai dari ujung(Vertex) kepala sama dengan tulang ekor.

b) The Biparietal diameter (BPD) adalah diameter antara 2 sisikepala. Pemeriksaan ini dilakukan setelah 13 minggu. Pada

umum nya ukuran BPD meningkat dari 2.4 cm (13 minggu)sampai dengan 9.4 cm (at term). Different babies of the sameweight can have different head size, therefore dating in thelater part of pregnancy is generally considered unreliable.(Chartand furthercomments) Dating using the BPD shouldbe done as early as is feasible.

c)The Femur length(FL) Measures the longest bone in the bodyand reflects the longitudinal growth of the fetus. Its

usefulness is similar to the BPD. It increases from about 1.5cm at 14 weeks to about 7.8 cm at term. (Chartand furthercomments) Similar to the BPD, dating using the FL should bedone as early as is feasible.

d) The Abdominal circumference (AC) The single mostimportant measurement to make in late pregnancy. It reflectsmore of fetal size and weight rather than age. Serialmeasurements are useful in monitoring growthof the fetus.(Chartand furthercomments) AC measurements should not

be used for dating a fetus.

Other important measurements are discussedhere.

The weight of the fetus at any gestation can also be estimated withgreat accuracy using polynomial equations containing the BPD,

FL, and AC. computer softwares and lookup charts are readilyavailable. For example, a BPD of 9.0 cm and an AC of 30.0 cm willgive a weight estimate of 2.85 kg. (comments)

4. Diagnosis of fetal malformation.

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Many structural abnormalities in the fetus can be reliablydiagnosed by an ultrasound scan, and these can usually be madebefore 20 weeks. Common examples include hydrocephalus,anencephaly, myelomeningocoele, achondroplasia and otherdwarfism, spina bifida, exomphalos, Gastroschisis, duodenalatresiaandfetal hydrops. With more recent equipment, conditionssuch ascleft lips/ palateandcongenital cardiac abnormalitiesaremore readily diagnosed and at an earlier gestational age. (Also seetheFAQandAnomaliespages).

First trimester ultrasonic 'soft' markers for chromosomalabnormalities such as the absence offetal nasal bone, an increasedfetal nuchal translucency(the area at the back of the neck) are now

in common use to enable detection ofDown syndromefetuses.

Read also: Soft Markers - A Guide for Professionals andUltrasonographic "soft markers" of fetal chromosomal defects.

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

5. Placental localization.

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Ultrasonography has become indispensible in the localization ofthe site of the placenta and determining its lower edges, thusmaking a diagnosis or an exclusion of placenta previa. Otherplacental abnormalities in conditions such as diabetes, fetalhydrops, Rh isoimmunization and severe intrauterine growthretardationcan also be assessed.

6. Multiple pregnancies.In this situation, ultrasonography is invaluable in determining thenumber of fetuses, thechorionicity, fetal presentations, evidence ofgrowth retardation and fetal anomaly, the presence of placentaprevia, and any suggestion oftwin-to-twin transfusion.

7. Hydramnios and Oligohydramnios.Excessive or decreased amount of liquor (amniotic fluid) can beclearly depicted by ultrasound. Both of these conditions can have

adverse effects on the fetus. In both these situations, carefulultrasound examination should be made to exclude intraulterinegrowth retardationand congenital malformation in the fetus suchas intestinal atresia, hydrops fetalis or renal dysplasia. See alsoFAQandcomments.

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 pregnancye.g. fibromyomata and ovarian cyst.

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