Obstetric ultrasonography

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Obstetric ultrasonography
Obsteric ultrasonograph.jpg
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.
Other namesPrenatal Ultrasound
ICD-9-CM 88.78
MeSH D016216
OPS-301 code 3-032, 3-05d

Obstetric ultrasonography, or prenatal ultrasound, 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 the 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.

Contents

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 (the anatomy scan) in order to confirm pregnancy dating, to measure the fetus so that growth abnormalities can be recognized quickly later in pregnancy, and to assess for congenital malformations and multiple pregnancies (twins, etc). [1] Additionally, the ISUOG recommends that pregnant patients who desire genetic testing have obstetric ultrasounds between 11 weeks' and 13 weeks 6 days' gestational age in countries with resources to perform them (the nuchal scan). 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 infants. [3]

Terminology

Obstetric ultrasonography in Moscow, Russia, 2016 Ultrasono de abdomeno.jpg
Obstetric ultrasonography in Moscow, Russia, 2016

Below are useful terms on ultrasound: [4]

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.

Types

Traditional obstetric sonograms are done by placing a transducer on the abdomen of the pregnant woman. One variant, 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 25 mm, about five and a half weeks. [10] The heartbeat is usually seen on transvaginal ultrasound by the time the embryo measures 5 mm, but may not be visible until the embryo reaches 19 mm, around 7 weeks' gestational age. [5] [11] [12] Coincidentally, most miscarriages also happen by 7 weeks' gestation. The rate of miscarriage, especially threatened miscarriage, drops significantly after normal heartbeat is detected, and after 13 weeks. [13]

First trimester

In the first trimester, a standard ultrasound examination typically includes: [12]

Second and third trimester

In the second trimester, a standard ultrasound exam typically includes: [12]

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.jpg
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. Biparietal diameter by gestational age.png
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.

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, across the two parietal bones), the head circumference, the length of the femur, the crown-heel length (head to heel), and other fetal parameters.[ citation needed ] 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]

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 Boy.JPG
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. [15] [16] [17] After 13 weeks' gestation, a high accuracy of between 99% and 100% is possible if the fetus does not display intersex external characteristics. [18]

The following is accuracy data from two hospitals:

Gestational AgeKing's College Hospital Medical School [16] Taipei City Hospital & Li Shin Hospital [17]
11 weeks70.3%71.9%
12 weeks98.7%92%
13 weeks100%98.3%

Influencing factors

The accuracy of fetal sex discernment depends on: [15]

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

Ultrasonography of the cervix

Fetus at 14 weeks (profile) Embryo at 14 weeks profile.JPG
Fetus at 14 weeks (profile)

Obstetric sonography is useful in the assessment of the cervix in women at risk for premature birth. A short cervix preterm is associated with a higher risk for premature delivery: At 24 weeks' gestation, a cervix length of less than 25 mm defines a risk group for spontaneous preterm birth. Further, the shorter the cervix, the greater the risk. [19] Cervical measurement on ultrasound also has been helpful to use ultrasonography in patients with preterm contractions, as those whose cervical length exceeds 30 mm are unlikely to deliver within the next week. [20]

Abnormality screening

In most countries, routine pregnancy sonographic 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 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 (called the "anatomy scan", "anomaly scan," or "level 2 ultrasound"). 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, [21] and general fetus well being. [22]

Second-trimester ultrasound screening for aneuploidies is based on looking for soft markers and some predefined structural abnormalities. Soft markers are variations from normal anatomy, which are more common in aneuploid fetuses compared to euploid ones. These markers are often not clinically significant and do not cause adverse pregnancy outcomes. [23]

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. [24] 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. [24]

The 1985 maximum power allowed by the U.S. Food and Drug Administration (FDA) of 180 milliwatts per square cm [25] 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. [26]

Doppler ultrasonography examinations has a thermal index (TI) of about five times that of regular (B-mode) ultrasound examinations. [24] 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. [24]

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. [27]

The American Institute of Ultrasound in Medicine recommends spectral Doppler only if M-mode sonography is unsuccessful, and even then only briefly, due to the acoustic intensity delivered to the fetus. [28]

History

Polaroid photograph of an obstetric ultrasound taken in 1985 Obstetric Ultrasound Polaroid Photograph 1985.jpg
Polaroid photograph of an obstetric ultrasound taken in 1985

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] [ self-published source? ]

In 1962, David Robinson, George Kossoff, George Radovanovich, and Dr William Garrett were the first in the world to identify a number of foetal anatomical structures from high frequency sound wave imaging. [31] [32]

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. [33] [ self-published source? ] 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.[ citation needed ]

In March and April 2015, a post by a pregnant woman named Jen Martin (née 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. [34] [35] [36]

Society 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. [37] 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 affect the way in which pregnancy is experienced and conceptualised. [37] This "technocratic takeover" [37] 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. [37] 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. [37]

Recent studies have stressed the importance of framing "reproductive health matters cross-culturally", particularly when understanding the "new phenomenon" of "the proliferation of ultrasound imaging" in developing countries. [38] In 2004, Tine Gammeltoft interviewed 400 women in Hanoi's Obstetrics and Gynecology Hospital; each "had an average of 6.6 scans during her pregnancy", much higher than five years prior when "a pregnant woman might or might not have had a single scan during her pregnancy" in Vietnam. [38] Gammeltoft explains that "many Asian countries" see "the foetus as an ambiguous being" unlike in Western medicine where it is common to think of the foetus as "materially stable". [38] Therefore, although women, particularly in Asian countries, "express intense uncertainties regarding the safety and credibility of this technology", it is overused for its "immediate reassurance". [38]

See also

Related Research Articles

Obstetrics is the field of study concentrated on pregnancy, childbirth and the postpartum period. As a medical specialty, obstetrics is combined with gynecology under the discipline known as obstetrics and gynecology (OB/GYN), which is a surgical field.

<span class="mw-page-title-main">Ectopic pregnancy</span> Female reproductive system health issue

Ectopic pregnancy is a complication of pregnancy in which the embryo attaches outside the uterus. Signs and symptoms classically include abdominal pain and vaginal bleeding, but fewer than 50 percent of affected women have both of these symptoms. The pain may be described as sharp, dull, or crampy. Pain may also spread to the shoulder if bleeding into the abdomen has occurred. Severe bleeding may result in a fast heart rate, fainting, or shock. With very rare exceptions, the fetus is unable to survive.

<span class="mw-page-title-main">Amniocentesis</span> Sampling of amniotic fluid done mainly to detect fetal chromosomal abnormalities

Amniocentesis is a medical procedure used primarily in the prenatal diagnosis of genetic conditions. It has other uses such as in the assessment of infection and fetal lung maturity. Prenatal diagnostic testing, which includes amniocentesis, is necessary to conclusively diagnose the majority of genetic disorders, with amniocentesis being the gold-standard procedure after 15 weeks' gestation.

<span class="mw-page-title-main">Prenatal testing</span> Testing for diseases or conditions in a fetus

Prenatal testing is a tool that can be used to detect some birth defects at various stages prior to birth. Prenatal testing consists of prenatal screening and prenatal diagnosis, which are aspects of prenatal care that focus on detecting problems with the pregnancy as early as possible. These may be anatomic and physiologic problems with the health of the zygote, embryo, or fetus, either before gestation even starts or as early in gestation as practicable. Screening can detect problems such as neural tube defects, chromosome abnormalities, and gene mutations that would lead to genetic disorders and birth defects, such as spina bifida, cleft palate, Down syndrome, trisomy 18, Tay–Sachs disease, sickle cell anemia, thalassemia, cystic fibrosis, muscular dystrophy, and fragile X syndrome. Some tests are designed to discover problems which primarily affect the health of the mother, such as PAPP-A to detect pre-eclampsia or glucose tolerance tests to diagnose gestational diabetes. Screening can also detect anatomical defects such as hydrocephalus, anencephaly, heart defects, and amniotic band syndrome.

<span class="mw-page-title-main">Placenta praevia</span> Medical condition

Placenta praevia is when the placenta attaches inside the uterus but in a position near or over the cervical opening. Symptoms include vaginal bleeding in the second half of pregnancy. The bleeding is bright red and tends not to be associated with pain. Complications may include placenta accreta, dangerously low blood pressure, or bleeding after delivery. Complications for the baby may include fetal growth restriction.

In obstetrics, gestational age is a measure of the age of a pregnancy taken from the beginning of the woman's last menstrual period (LMP), or the corresponding age of the gestation as estimated by a more accurate method, if available. Such methods include adding 14 days to a known duration since fertilization, or by obstetric ultrasonography. The popularity of using this measure of pregnancy is largely due to convenience: menstruation is usually noticed, while there is generally no convenient way to discern when fertilization or implantation occurred.

<span class="mw-page-title-main">Fetoscopy</span> Endoscopic procedure during pregnancy

Fetoscopy is an endoscopic procedure during pregnancy to allow surgical access to the fetus, the amniotic cavity, the umbilical cord, and the fetal side of the placenta. A small (3–4 mm) incision is made in the abdomen, and an endoscope is inserted through the abdominal wall and uterus into the amniotic cavity. Fetoscopy allows for medical interventions such as a biopsy or a laser occlusion of abnormal blood vessels or the treatment of spina bifida.

<span class="mw-page-title-main">Pregnancy</span> Time of offspring development in mothers body

Pregnancy is the time during which one or more offspring develops (gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins.

Cervical weakness, also called cervical incompetence or cervical insufficiency, is a medical condition of pregnancy in which the cervix begins to dilate (widen) and efface (thin) before the pregnancy has reached term. Definitions of cervical weakness vary, but one that is frequently used is the inability of the uterine cervix to retain a pregnancy in the absence of the signs and symptoms of clinical contractions, or labor, or both in the second trimester. Cervical weakness may cause miscarriage or preterm birth during the second and third trimesters. It has been estimated that cervical insufficiency complicates about 1% of pregnancies, and that it is a cause in about 8% of women with second trimester recurrent miscarriages.

Postterm pregnancy is when a woman has not yet delivered her baby after 42 weeks of gestation, two weeks beyond the typical 40-week duration of pregnancy. Postmature births carry risks for both the mother and the baby, including fetal malnutrition, meconium aspiration syndrome, and stillbirths. After the 42nd week of gestation, the placenta, which supplies the baby with nutrients and oxygen from the mother, starts aging and will eventually fail. Postterm pregnancy is a reason to induce labor.

<span class="mw-page-title-main">Nuchal scan</span> Routine ultrasound done between 11 and 14 weeks pregnancy

A nuchal scan or nuchal translucency (NT) scan/procedure is a sonographic prenatal screening scan (ultrasound) to detect chromosomal abnormalities in a fetus, though altered extracellular matrix composition and limited lymphatic drainage can also be detected.

A Doppler fetal monitor is a hand-held ultrasound transducer used to detect the fetal heartbeat for prenatal care. It uses the Doppler effect to provide an audible simulation of the heart beat. Some models also display the heart rate in beats per minute (BPM). Use of this monitor is sometimes known as Doppler auscultation. The Doppler fetal monitor is commonly referred to simply as a Doppler or fetal Doppler. It may be classified as a form of Doppler ultrasonography.

<span class="mw-page-title-main">Velamentous cord insertion</span> Velamentous placenta

Velamentous cord insertion is a complication of pregnancy where the umbilical cord is inserted in the fetal membranes. It is a major cause of antepartum hemorrhage that leads to loss of fetal blood and associated with high perinatal mortality. In normal pregnancies, the umbilical cord inserts into the middle of the placental mass and is completely encased by the amniotic sac. The vessels are hence normally protected by Wharton's jelly, which prevents rupture during pregnancy and labor. In velamentous cord insertion, the vessels of the umbilical cord are improperly inserted in the chorioamniotic membrane, and hence the vessels traverse between the amnion and the chorion towards the placenta. Without Wharton's jelly protecting the vessels, the exposed vessels are susceptible to compression and rupture.

<span class="mw-page-title-main">Chorionic hematoma</span> Medical condition

Chorionic hematoma is the pooling of blood (hematoma) between the chorion, a membrane surrounding the embryo, and the uterine wall. It occurs in about 3.1% of all pregnancies, it is the most common sonographic abnormality and the most common cause of first trimester bleeding.

The following outline is provided as an overview of and topical guide to obstetrics:

<span class="mw-page-title-main">Products of conception</span>

Products of conception, abbreviated POC, is a medical term used for the tissue derived from the union of an egg and a sperm. It encompasses anembryonic gestation which does not have a viable embryo.

Early pregnancy bleeding is vaginal bleeding before 14 weeks of gestational age. If the bleeding is significant, hemorrhagic shock may occur. Concern for shock is increased in those who have loss of consciousness, chest pain, shortness of breath, or shoulder pain.

The anomaly scan, also sometimes called the anatomy scan, 20-week ultrasound, or level 2 ultrasound, evaluates anatomic structures of the fetus, placenta, and maternal pelvic organs. This scan is an important and common component of routine prenatal care. The function of the ultrasound is to measure the fetus so that growth abnormalities can be recognized quickly later in pregnancy, to assess for congenital malformations and multiple pregnancies, and to plan method of delivery.

Beryl Rice Benacerraf was an American radiologist and professor of obstetrics, gynecology and reproductive biology and radiology at Harvard Medical School. She was a pioneer in the use of prenatal ultrasound to diagnose fetal abnormalities, including Down syndrome. In 2021, she was recognized as a "Giant in Obstetrics and Gynecology" by the American Journal of Obstetrics & Gynecology.

Pregnancy in a rudimentary horn of the uterus is a very rare type of ectopic pregnancy. This type of pregnancy can be life-threatening, as the rudimentary horn is not meant to sustain a pregnancy and is at risk of rupturing.

References

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  28. ↑ "Statement on Measurement of the Fetal Heart Rate". Sound Waves Weekly. American Institute of Ultrasound in Medicine. November 17, 2011. Archived from the original on January 21, 2023. Retrieved May 11, 2017. When attempting to obtain fetal heart rate with a diagnostic ultrasound system, the AIUM recommends using M-mode at first because the time-averaged acoustic intensity delivered to the fetus is lower with M-mode than with spectral Doppler. If this is unsuccessful, spectral Doppler ultrasound may be used with the following guidelines: use spectral Doppler only briefly (eg, 4-5 heart beats), and keep the thermal index (TIS for soft tissues in the first trimester and TIB for bones in second and third trimesters) as low as possible, preferably below 1 in accordance with the ALARA (as low as reasonably achievable) principle.
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  35. ↑ "Ultrasound Shows Baby Clapping To 'If You're Happy And You Know It'". inquisitr.com. 28 March 2015. Retrieved 21 March 2018.
  36. ↑ "Viral Ultrasound Video of Clapping Fetus is Not Fake, Mom Insists". Archived from the original on 2015-04-13. Retrieved 2015-04-04.
  37. 1 2 3 4 5 [Gammeltoft, Tine, 2007, Sonography and Sociality – Obstetrical Ultrasound Imagining in Urban Vietnam, Medical Anthropology Quarterly, 21:2, 133-153]
  38. 1 2 3 4 Gammeltoft, Tine (2007). "Sonography and Sociality: Obstetrical Ultrasound Imaging in Urban Vietnam". Medical Anthropology Quarterly. 21 (2): 133–53. doi:10.1525/maq.2007.21.2.133. PMID   17601081.
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