Obstetric ultrasonography
576327
220757356
2008-06-21T12:43:18Z
DOI bot
6652755
Citation maintenance. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]].
[[Image:Obsteric_ultrasonograph.jpg|thumb|300px|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.]]
'''Obstetric sonography''' (ultrasonography) is the application of [[medical ultrasonography]] to [[obstetrics]], in which ultrasound is used to visualize the [[embryo]] or [[fetus]] in its mother's [[uterus]] (womb). The procedure is often a standard part of [[prenatal]] care, as it yields a variety of information regarding the health of the mother and of the fetus, as well as regarding the progress of the pregnancy.
==Types==
Traditional obstetric ultrasounds are done by placing a [[transducer]] (a probe that emits high frequency sound waves) on the abdomen of the pregnant woman. One variant is a ''transvaginal ultrasound'' 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 ultrasound'' which detects the heartbeat of the fetus. Doppler ultrasound can be used to evaluate the pulsations in the fetal heart and bloods vessels for signs of abnormalities.<!--
--><ref name="woo">{{cite web | last = Woo | first = Joseph | title = Why and when is Ultrasound used in Pregnancy? | work = Obstetric Ultrasound: A Comprehensive Guide | date = 2006 | url = http://www.ob-ultrasound.net/ | accessdate = 2007-05-27 }}</ref>
==Early pregnancy==
The [[gestational sac]] can sometimes be visualized as early as four and a half weeks of [[gestational age|gestation]] (approximately two and a half weeks after ovulation) and the [[yolk sac]] at about five weeks gestation. The [[Embryo#The human embryo|embryo]] can be observed and measured by about five and a half weeks. The heartbeat may be seen as early as 6 weeks, and is usually visible by 7 weeks gestation.<ref name="woo" /><!--
--><ref name="boschert">{{cite journal |author=Boschert, Sherry |title=Anxious Patients Often Want Very Early Ultrasound Exam |journal=OB/GYN News |publisher=FindArticles.com |date=[[2001-06-15]] |url=http://findarticles.com/p/articles/mi_m0CYD/is_12_36/ai_76636730 |accessdate=2007-05-27}}</ref>
==Dating and growth monitoring==
[[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 gestation, the fetal age may be estimated by the biparietal diameter (the diameter of the head) and the length of the femur (the longest bone in the body). 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.<ref name="woo" />
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.<ref name="woo" />
==Fetal Sex Determination==
[[Image:Boy.JPG|thumb|right|Boy]]
The [[sex]] of the baby can usually be determined by ultrasound at any time after 16 weeks, often at the dating scan around 20 weeks into the pregnancy depending upon the quality of the sonographic machine and skill of the operator. This is also the best time to have an ultrasound done as most infants are the same size at this stage of development. Depending on the skill of the sonographer, ultrasound may suffer from a high rate of false negatives and false positives. This means care has to be taken in interpreting the accuracy of the scan.
[[Image:Embryo at 14 weeks profile.JPG|thumb|right|Fetus at 14 weeks (profile)]]
==Abnormality Screening==
In some countries, routine [[pregnancy]] ultrasound scans are performed to detect developmental defects before birth. This includes checking the status of the limbs and vital organs, as well as (sometimes) specific tests for abnormalities. Some abnormalities detected by ultrasound can be addressed by medical treatment [[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 are in fact normal.
==History==
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 [[United States Public Health Service|U.S. Public Health Services]] and the [[University of Colorado Denver|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.<!--
--><ref>{{cite web | last = Woo | first = Joseph | title = A short History of the development of Ultrasound in Obstetrics and Gynecology | publisher = ob-ultrasound.net | date = 2002 | url = http://www.ob-ultrasound.net/history1.html | accessdate = 2007-08-26 }}</ref> 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|Acuson Corporation's]] pioneering work on the development of Coherent Image Formation helped shape the development of diagnostic ultrasound equipment as a whole.
==Safety issues==
Current evidence indicates that diagnostic ultrasound is safe for the unborn child, unlike [[radiograph]]s, which employ [[ionizing radiation]]. However, no [[randomized controlled trial]]s have been undertaken to test the safety of the technology, and thus ultrasound procedures are generally not done repeatedly unless medically called for.
A 2006 study on mice exposed to ultrasound showed neurological changes in the exposed fetuses. Some of the rodent brain cells failed to migrate to their proper position and remained scattered in incorrect parts of the brain.<!--
--><ref>{{cite journal |author=Ang ES, Gluncic V, Duque A, Schafer ME, Rakic P |title=Prenatal exposure to ultrasound waves impacts neuronal migration in mice |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=103 |issue=34 |pages=12903–10 |year=2006 |pmid=16901978 |doi=10.1073/pnas.0605294103 |accessdate=2007-05-28}}</ref>
It has been shown that [[LIPUS|Low Intensity Pulsed Ultrasound]] does have a localized effect on growth in human beings. The 1985 FDA-allowed maximum power of 180 milliwatts per square cm <ref>http://www.nanomedicine.com/NMI/6.4.1.htm expressed as 1800 watts per m^2</ref> is well under the 30-80 milliwatts per square cm range of the Statison V veterinary LIPUS device<ref>http://www.statison.com/html/Statison_V_User_Guide.pdf</ref>. LIPUS has been shown to effect tissue growth in as little as 20 minutes of time with repeated daily applications. Adding to the similarity, LIPUS and medical ultrasound both operate in the 1 to 10MHz range.
While the benefits of medical ultrasound probably outweigh any risks, vanity uses such as making [[3D ultrasound]] movies without a doctors order present an obviously unnecessary but unknown risk to a developing fetus. Clinical guidelines produced by the Society of Obstetricians and Gynaecologists of Canada recommend against the non-medical use of fetal ultrasound. <ref>[http://www.sogc.org/health/pregnancy-ultrasound_e.asp Ultasound in Pregnancy]. Article by the Society of Obstetricians and Gynaecologists of Canada. Accessed 2008-04-09</ref>
==See also==
*[[Gynecologic ultrasonography]]
==External links==
* [http://www.radiologyinfo.org/en/info.cfm?pg=obstetricus RadiologyInfo: Obstetric Ultrasound Imaging]
* [http://www.obstetrics.co.nz/nuchal-translucency.html Nuchal Translucency test information page]
* [http://www.fda.gov/cdrh/consumer/fetalvideos.html FDA statement on Fetal Keepsake Videos]
* [http://www.aium.org/patient/entertainment/statements.pdf AIUM statement on prudent use of Ultrasound]
== References ==
{{reflist}}
{{Pregnancy}}
[[Category:Obstetrics]]
[[Category:Radiology]]
[[Category:Pregnancy tests]]
[[Category:Medical ultrasound]]
[[fr:Échographie obstétrique]]
[[he:בדיקת אולטרה סאונד להיריון]]
[[pl:Położnicze badanie ultrasonograficzne]]