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Obstetric ultrasonography

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Title: Obstetric ultrasonography  
Author: World Heritage Encyclopedia
Language: English
Subject: Obstetrics, 3D ultrasound, Medical ultrasound, Vibroacoustic stimulation, Fetal circulation
Collection: Articles Containing Video Clips, Medical Ultrasonography, Prenatal Sex Discernment, Tests During Pregnancy
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Obstetric ultrasonography

Obstetric Ultrasonography
Obstetric sonogram of a fetus at 16 weeks. The bright white circle center-right is the head, which faces to the left. Features include the forehead at 10 o'clock, the left ear toward the center at 7 o'clock and the right hand covering the eyes at 9:00.
ICD-9-CM 88.78
OPS-301 code 3-032, 3-05d

Obstetric ultrasonography is the use of medical ultrasonography in pregnancy, in which sound waves are used to create real-time visual images of the developing embryo or fetus in its mother's uterus (womb). The procedure is a standard part of prenatal care in many countries, as it can provide a variety of information about the health of the mother, the timing and progress of the pregnancy, and the health and development of the embryo or fetus.

The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) recommends that pregnant women have routine obstetric ultrasounds between 18 weeks and 22 weeks gestational age in order to confirm pregnancy timing, to measure the fetus so that growth abnormalities can be recognized quickly later in pregnancy, and to assess for congenital malformations and multiple gestations (i.e. twins).[1] Additionally, the ISUOG recommends that pregnant women have obstetric ultrasounds between 11 weeks and 13 weeks 6 days gestational age In countries with resources to perform them. Performing an ultrasound at this early stage of pregnancy can more accurately confirm the timing of the pregnancy and can also assess for multiple fetuses and major congenital abnormalities at an earlier stage. [2] Research shows that routine obstetric ultrasound before 24 weeks gestational age can significantly reduce the risk of failing to recognize multiple gestations and can improve pregnancy dating to reduce the risk of labor induction for post-dates pregnancy. There is no difference, however, in perinatal death or poor outcomes for babies. [3]


  • Terminology 1
  • Types 2
    • 3D ultrasound 2.1
  • Medical uses 3
    • Early pregnancy 3.1
    • First trimester 3.2
    • Second and third trimester 3.3
    • Dating and growth monitoring 3.4
    • Fetal sex discernment 3.5
      • Influencing factors 3.5.1
    • Ultrasonography of the cervix 3.6
    • Abnormality screening 3.7
  • Safety issues 4
  • History 5
  • Social and culture 6
  • See also 7
  • References 8
  • External links 9


Below are useful terms on ultrasound:[4]

  • Echogenic - giving rise to reflections (echoes) of ultrasound waves
  • Hyperechoic – more echogenic (brighter) than normal
  • Hypoechoic – less echogenic (darker) than normal
  • Isoechoic – the same echogenicity as another tissue
  • Transvaginal ultrasonography - Ultrasound is performed through the vagina
  • Transabdominal ultrasonography - Ultrasound is performed across the abdominal wall or through the abdominal cavity

In normal state, each body tissue type, such as liver, spleen or kidney, has a unique echogenicity. Fortunately, gestational sac, yolk sac and embryo are surrounded by hyperechoic (brighter) body tissues.


Traditional obstetric sonograms are done by placing a transducer on the abdomen of the pregnant woman. One variant, a transvaginal sonography, is done with a probe placed in the woman's vagina. Transvaginal scans usually provide clearer pictures during early pregnancy and in obese women. Also used is Doppler sonography which detects the heartbeat of the fetus. Doppler sonography can be used to evaluate the pulsations in the fetal heart and bloods vessels for signs of abnormalities.[5]

3D ultrasound

Modern 3D ultrasound images provide greater detail for prenatal diagnosis than the older 2D ultrasound technology.[6] While 3D is popular with parents desiring a prenatal photograph as a keepsake,[7] both 2D and 3D are discouraged by the FDA for non-medical use,[8] but there are no definitive studies linking ultrasound to any adverse medical effects.[9] The following 3D ultrasound images were taken at different stages of pregnancy:

Medical uses

Early pregnancy

A gestational sac can be reliably seen on transvaginal ultrasound by 5 weeks gestational age (approximately 3 weeks after ovulation).The embryo should be seen by the time the gestational sac measures 20mm, about five and a half weeks. The heartbeat is usually seen on transvaginal ultrasound by the time the embryo measures 5mm, but may not be visible until the embryo reaches 7mm, around 7 weeks gestational age. [5][10] [11] Coincidentally, most miscarriages also happen by 7 weeks gestation. The rate of miscarriage, especially threatened miscarriage, drops significantly if normal heartbeat is detected.[12]

First trimester

In the first trimester, a standard ultrasound examination typically includes:[13]

  • Gestational sac size, location, and number
  • Identification of the embryo and/or yolk sac
  • Measurement of fetal length (known as the crown-rump length)
  • Fetal number, including number of amnionic sacs and chorionic sacs for multiple gestations
  • Embryonic/fetal cardiac activity
  • Assessment of embryonic/fetal anatomy appropriate for the first trimester
  • Evaluation of the maternal uterus, tubes, ovaries, and surrounding structures
  • Evaluation of the fetal nuchal fold, with consideration of fetal nuchal translucency assessment

Second and third trimester

In the second trimester, a standard ultrasound exam typically includes:[14]

  • Fetal number, including number of amnionic sacs and chorionic sacs for multiple gestations
  • Fetal cardiac activity
  • Fetal position relative to the uterus and cervix
  • Location and appearance of the placenta, including site of umbilical cord insertion when possible
  • Amnionic fluid volume
  • Gestational age assessment
  • Fetal weight estimation
  • Fetal anatomical survey
  • Evaluation of the maternal uterus, tubes, ovaries, and surrounding structures when appropriate

Dating and growth monitoring

Biparietal diameter is taken as the maximal transverse diameter of in a visualization of the horizontal plane of the head.
Biparietal diameter (the transverse diameter of the head) by gestational age, with the blue line representing the mean and the green area representing the 90% prediction interval.[15]

Gestational age is usually determined by the date of the woman's last menstrual period, and assuming ovulation occurred on day fourteen of the menstrual cycle. Sometimes a woman may be uncertain of the date of her last menstrual period, or there may be reason to suspect ovulation occurred significantly earlier or later than the fourteenth day of her cycle. Ultrasound scans offer an alternative method of estimating gestational age. The most accurate measurement for dating is the crown-rump length of the fetus, which can be done between 7 and 13 weeks of gestation. After 13 weeks of gestation, the fetal age may be estimated using the biparietal diameter (the transverse diameter of the head), the head circumference, the length of the femur, the crown-heel length (head to heel), and other fetal parameters.[16] Dating is more accurate when done earlier in the pregnancy; if a later scan gives a different estimate of gestational age, the estimated age is not normally changed but rather it is assumed the fetus is not growing at the expected rate.[5]

Not useful for dating, the abdominal circumference of the fetus may also be measured. This gives an estimate of the weight and size of the fetus and is important when doing serial ultrasounds to monitor fetal growth.[5]

Fetal sex discernment

Sonogram of male fetus, with scrotum and penis in center of image

The sex of the fetus may be discerned by ultrasound as early as 11 weeks gestation. The accuracy is relatively imprecise when attempted early.[17][18][19] After 13 weeks gestation, a high accuracy of between 99% to 100% is possible if the fetus does not display intersex external characteristics.[20]

The following is accuracy data from two hospitals:
Gestational Age King's College Hospital Medical School[18] Taipei City Hospital & Li Shin Hospital[19]
11 weeks 70.3% 71.9%
12 weeks 98.7% 92%
13 weeks 100% 98.3%

Influencing factors

The accuracy of fetal sex discernment depends on:[17]

  • Gestational age
  • Precision of sonographic machine
  • Expertise of the operator
  • Fetal posture

Ultrasonography of the cervix

Fetus at 14 weeks (profile)

Obstetric sonography has become useful in the assessment of the cervix in women at risk for premature birth. A short cervix preterm is undesirable: At 24 weeks gestation a cervix length of less than 25 mm defines a risk group for preterm birth, further, the shorter the cervix the greater the risk.[21] It also has been helpful to use ultrasonography in women with preterm contractions, as those whose cervix length exceed 30 mm are unlikely to deliver within the next week.[22]

Abnormality screening

In some countries, routine in utero or by perinatal care, though indications of other abnormalities can lead to a decision regarding abortion.

Perhaps the most common such test uses a measurement of the nuchal translucency thickness ("NT-test", or "Nuchal Scan"). Although 91% of fetuses affected by Down syndrome exhibit this defect, 5% of fetuses flagged by the test do not have Down syndrome.

Ultrasound may also detect fetal organ anomaly. Usually scans for this type of detection are done around 18 to 23 weeks of gestational age. Some resources indicate that there are clear reasons for this and that such scans are also clearly beneficial because ultrasound enables clear clinical advantages for assessing the developing fetus in terms of morphology, bone shape, skeletal features, fetal heart function, volume evaluation, fetal lung maturity,[23] and general fetus well being.[24]

Safety issues

3D rendering of the fetal spine in a scan at 19 weeks of pregnancy

Current evidence indicates that diagnostic ultrasound is safe for the unborn child, unlike radiographs, which employ ionizing radiation. Randomized controlled trials have followed children up to ages 8–9, with no significant differences in vision, hearing, school performance, dyslexia, or speech and neurologic development by exposure to ultrasound.[25] In one randomized trial, the children with greater exposure to ultrasound had a reduction in perinatal mortality, and was attributed to the increased detection of anomalies in the ultrasound group.[25]

The 1985 maximum power allowed by the U.S. Food and Drug Administration (FDA) of 180 milliwatts per square cm [26] is well under the levels used in therapeutic ultrasound, but still higher than the 30-80 milliwatts per square cm range of the Statison V veterinary LIPUS device.[27]

Doppler ultrasonography examinations has a thermal index (TI) of about five times that of regular (B-mode) ultrasound examinations.[25] Several randomized controlled trials have reported no association between Doppler exposure and birth weight, Apgar scores, and perinatal mortality. One randomized controlled trial, however, came to the result of a higher perinatal death rate of normally formed infants born after 24 weeks exposed to Doppler ultrasonography (RR 3.95, 95% CI 1.32–11.77), but this was not a primary outcome of the study, and has been speculated to be due to chance rather than a harmful effect of Doppler itself.[25]

The FDA discourages its use for non-medical purposes such as fetal keepsake videos and photos, even though it is the same technology used in hospitals.[28]


Scottish physician Ian Donald was one of the pioneers of medical use of ultrasound. His article "Investigation of Abdominal Masses by Pulsed Ultrasound" was published in The Lancet in 1958.[29] Donald was Regius Professor of Midwifery at the University of Glasgow.[30]

In 1962, after about two years of work, Joseph Holmes, William Wright, and Ralph Meyerdirk developed the first compound contact B-mode scanner. Their work had been supported by U.S. Public Health Services and the University of Colorado. Wright and Meyerdirk left the university to form Physionic Engineering Inc., which launched the first commercial hand-held articulated arm compound contact B-mode scanner in 1963.[31] This was the start of the most popular design in the history of ultrasound scanners.

Obstetric ultrasound has played a significant role in the development of diagnostic ultrasound technology in general. Much of the technological advances in diagnostic ultrasound technology are due to the drive to create better obstetric ultrasound equipment. Acuson Corporation's pioneering work on the development of Coherent Image Formation helped shape the development of diagnostic ultrasound equipment as a whole.

In March and April of 2015, a post by a pregnant woman named Jen Martin (nee Cardinal) and her husband to YouTube, which had been viewed at least 2 million times and had many likes, showed the 14-week-old fetus clapping repeatedly to the song, sung by the parents, "If You're Happy And You Know It." It was later revealed that the video- while not a fake- had been somewhat edited to show more fetal claps than likely occurred. It is not unprecedented for fetuses of that age to make momentary movements that could be repeated once or twice beyond the initial movement, according to experts, but to repeat such a movement more than that- especially purposefully- would not likely be feasible at that point.[32][33][34]

Social and culture

The increasingly widespread use of ultrasound technology in monitoring pregnancy has had a great impact on the way in which women and societies at large conceptualise and experience pregnancy and childbirth.[35] The pervasive spread of obstetric ultrasound technology around the world and the conflation of its use with creating a ‘safe’ pregnancy as well as the ability to see and determine features like the sex of the fetus impact the way in which pregnancy is experienced and conceptualised.[35] This “technocratic takeover” [35] of pregnancy is not limited to western or developed nations but also affects conceptualisations and experiences in developing nations and is an example of the increasing medicalisation of pregnancy, a phenomenon that has social as well as technological ramifications.[35] Ethnographic research concerned with the use of ultrasound technology in monitoring pregnancy can show us how it has changed the embodied experience of expecting mothers around the globe.[35]

See also


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  5. ^ a b c d
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  17. ^ a b
  18. ^ a b
  19. ^ a b
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  24. ^
  25. ^ a b c d
  26. ^
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  28. ^
  29. ^
  30. ^ in 1958LancetIan Donald's paper in the by Joseph Woo
  31. ^
  32. ^
  33. ^
  34. ^
  35. ^ a b c d e [Gammeltoft, Tine, 2007, Sonography and Sociality – Obstetrical Ultrasound Imagining in Urban Vietnam, Medical Anthropology Quarterly, 21:2, 133-153]

External links

  • RadiologyInfo: Obstetric Ultrasound Imaging
  • AIUM statement on prudent use of Ultrasound
  • The Global Library of Women's Medicine Imaging in Obstetrics and Gynecology link
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