Obstetric 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 surgic ...

ultrasonography, or prenatal ultrasound, is the use of

medical ultrasonography Medical ultrasound includes diagnostic techniques (mainly medical imaging, imaging techniques) using ultrasound, as well as therapeutic ultrasound, therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal ...

pregnancy 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. Pregnancy usually occurs by sexual intercourse, but ca ...

, in which sound waves are used to create real-time visual images of the developing

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...

in the

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...

(womb). The procedure is a standard part of

prenatal Prenatal development () includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal devel ...

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 The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG, the Society for Women's Imaging) is a professional membership association and charity registered in England and Wales. ISUOG represents and supports professionals using ...

(ISUOG) recommends that pregnant women have routine

obstetric 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 surgic ...

ultrasounds between 18 weeks' and 22 weeks'

gestational age In obstetrics, gestational age is a measure of the age of a pregnancy which is 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. Suc ...

(the

anatomy scan 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 prenat ...

) 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 A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can r ...

and

multiple pregnancies A multiple birth is the culmination of one multiple pregnancy, wherein the mother gives birth to two or more babies. A term most applicable to vertebrate species, multiple births occur in most kinds of mammals, with varying frequencies. Such bir ...

(twins, etc). 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 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 ...

). 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. Research shows that routine

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 Labor induction is the process or treatment that stimulates childbirth and delivery. Inducing (starting) labor can be accomplished with pharmaceutical or non-pharmaceutical methods. In Western countries, it is estimated that one-quarter of pregnan ...

for post-dates pregnancy. There is no difference, however, in

perinatal Prenatal development () includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal devel ...

death or poor outcomes for infants.

Terminology

Below are useful terms on ultrasound: * 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 Vaginal ultrasonography is a medical ultrasonography that applies an ultrasound transducer (or "probe") in the vagina to visualize organs within the pelvic cavity. It is also called transvaginal ultrasonography because the ultrasound waves go ''a ...

– 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 Echogenicity (misspelled sometimes as echogenecity) or echogeneity is the ability to bounce an echo, e.g. return the signal in ultrasound examinations. In other words, echogenicity is higher when the surface bouncing the sound echo reflects increa ...

. Fortunately, gestational sac, yolk sac and embryo are surrounded by hyperechoic (brighter) body tissues.

Types

Traditional obstetric sonograms are done by placing a

transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and contr ...

on the

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

of the pregnant woman. One variant, ''transvaginal sonography,'' is done with a probe placed in the woman's

vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...

. Transvaginal scans usually provide clearer pictures during early pregnancy and in

obese Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's we ...

women. Also used is ''

Doppler sonography Doppler ultrasonography is medical ultrasonography that employs the Doppler effect to perform imaging of the movement of tissues and body fluids (usually blood), and their relative velocity to the probe. By calculating the frequency shift of ...

'' 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.

3D ultrasound

Modern

3D ultrasound 3D ultrasound is a medical ultrasound technique, often used in fetal, cardiac, trans-rectal and intra-vascular applications. 3D ultrasound refers specifically to the volume rendering of ultrasound data. When involving a series of 3D volumes collec ...

images provide greater detail for prenatal diagnosis than the older 2D ultrasound technology. While 3D is popular with parents desiring a prenatal photograph as a keepsake, both 2D and 3D are discouraged by the

FDA The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food s ...

for non-medical use, but there are no definitive studies linking ultrasound to any adverse medical effects. The following 3D ultrasound images were taken at different stages of pregnancy: Image:Fetal movements 3D Ultrasound Dr. Wolfgang Moroder.theora.ogv, 3D Ultrasound of fetal movements at 12 weeks Image:Ultrasound_image_of_a_fetus.jpg, 75-mm fetus (about 14 weeks'

) Image:Sucking his thumb and waving.jpg, Fetus at 17 weeks Image:3dultrasound 20 weeks.jpg, Fetus at 20 weeks

Medical uses

Early pregnancy

gestational sac The gestational sac is the large cavity of fluid surrounding the embryo. During early embryogenesis it consists of the extraembryonic coelom, also called the chorionic cavity. The gestational sac is normally contained within the uterus. It is the o ...

can be reliably seen on transvaginal ultrasound by 5 weeks' gestational age (approximately 3 weeks after ovulation). The

should be seen by the time the gestational sac measures 25 mm, about five-and-a-half weeks. The

heartbeat A heartbeat is one cardiac cycle of the heart. Heartbeat, heart beat, heartbeats, and heart beats may refer to: Computing *Heartbeat (computing), a periodic signal to indicate normal operation or to synchronize parts of a system *Heartbeat, clus ...

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. Coincidentally, most

miscarriages Miscarriage, also known in medical terms as a spontaneous abortion and pregnancy loss, is the death of an embryo or fetus before it is able to survive independently. Miscarriage before 6 weeks of gestation is defined by ESHRE as biochemical lo ...

also happen by 7 weeks' gestation. The rate of miscarriage, especially threatened miscarriage, drops significantly after normal heartbeat is detected, and after 13 weeks. File:Ultrasound of embryo at 5 weeks.png, Contents in the cavity of the

seen at approximately 5 weeks of

. File:Ultrasound of embryo at 5 weeks, colored.png, Artificially colored, showing

yolk sac The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac'' is far ...

and

(measuring 3 mm as the distance between the + signs). File:Heartbeat at 5 weeks 1 day.gif, Embryo at 5 weeks and 1 day of gestational age (at top left) with discernible

. File:Embryo at 5 weeks 5 days with heartbeat.gif, Embryo at 5 weeks and 5 days of gestational age with discernible heartbeat.

First trimester

In the first trimester, a standard ultrasound examination typically includes: * 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 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 ...

assessment

Second and third trimester

In the second trimester, a standard ultrasound exam typically includes: * 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

Gestational age In obstetrics, gestational age is a measure of the age of a pregnancy which is 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. Suc ...

is usually determined by the date of the woman's last menstrual period, and assuming ovulation occurred on day fourteen of the

menstrual cycle The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that make pregnancy possible. The ovarian cycle controls the production and release of eggs a ...

. 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 Crown-rump length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump). It is typically determined from ultrasound imagery and can be used to estimate gestationa ...

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 bone The parietal bones () are two bones in the Human skull, skull which, when joined at a fibrous joint, form the sides and roof of the Human skull, cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, an ...

s), the head circumference, the length of the

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...

, the crown-heel length (head to heel), and other fetal parameters. 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. 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.

Fetal sex discernment

The sex of the fetus may be discerned by ultrasound as early as 11 weeks' gestation. The accuracy is relatively imprecise when attempted early. After 13 weeks' gestation, a high accuracy of between 99% and 100% is possible if the fetus does not display intersex external characteristics. The following is accuracy data from two hospitals:

Influencing factors

The accuracy of fetal sex discernment depends on: * Gestational age * Precision of sonographic machine * Expertise of the operator * Fetal posture

Ultrasonography of the cervix

Obstetric sonography is useful in the assessment of the cervix in women at risk for

premature birth Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between 2 ...

. 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. 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.

Abnormality screening

In most countries, routine

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 ''In Utero'' is the third and final studio album by American rock band Nirvana. It was released on September 21, 1993, by DGC Records. After breaking into the mainstream with their second album, ''Nevermind'' (1991), Nirvana hired Steve Albini t ...

or by

care, though indications of other abnormalities can lead to a decision regarding

abortion Abortion is the termination of a pregnancy by removal or expulsion of an embryo or fetus. An abortion that occurs without intervention is known as a miscarriage or "spontaneous abortion"; these occur in approximately 30% to 40% of pregn ...

. Perhaps the most common such test uses a measurement of the

thickness ("NT-test", or "

Nuchal Scan 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 ...

"). Although 91% of fetuses affected by

Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...

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

(called the "

", "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, and general fetus well being. 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.

Safety issues

Current evidence indicates that diagnostic ultrasound is safe for the unborn child, unlike

radiographs Radiography is an imaging technology, imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical radiography ("diagnos ...

, which employ

ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...

Randomized controlled trial A randomized controlled trial (or randomized control trial; RCT) is a form of scientific experiment used to control factors not under direct experimental control. Examples of RCTs are clinical trials that compare the effects of drugs, surgical te ...

s 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. 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. The 1985 maximum power allowed by the U.S.

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respon ...

(FDA) of 180 milliwatts per square cm is well under the levels used in

therapeutic ultrasound Therapeutic ultrasound refers generally to any type of ultrasonic procedure that uses ultrasound for therapeutic benefit. Physiotherapeutic ultrasound was introduced into clinical practice in the 1950s, with lithotripsy introduced in the 1980s. ...

, but still higher than the 30-80 milliwatts per square cm range of the Statison V veterinary LIPUS device.

Doppler ultrasonography Doppler ultrasonography is medical ultrasonography that employs the Doppler effect to perform imaging of the movement of tissues and body fluids (usually blood), and their relative velocity to the probe. By calculating the frequency shift of ...

examinations has a thermal index (TI) of about five times that of regular (B-mode) ultrasound examinations. Several randomized controlled trials have reported no association between Doppler exposure and birth weight,

Apgar scores The Apgar score is a quick way for doctors to evaluate the health of all newborns at 1 and 5 minutes after birth and in response to resuscitation. It was originally developed in 1952 by an anesthesiologist at Columbia University, Virginia Apgar, ...

, 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. 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. The

American Institute of Ultrasound in Medicine The American Institute of Ultrasound in Medicine (AIUM) is a multidisciplinary association dedicated to advancing the use of ultrasound in medicine through professional and public education, research, development of guidelines, and accreditation. ...

recommends spectral Doppler only if M-mode sonography is unsuccessful, and even then only briefly, due to the acoustic intensity delivered to the fetus.

History

Obstetric Ultrasound Polaroid Photograph 1985

Scottish physician

Ian Donald Ian Donald (27 December 1910 – 19 June 1987) was an English physician who pioneered the diagnostic use of ultrasound in obstetrics, enabling the visual discovery of abnormalities during pregnancy. Donald was born in Cornwall, England, to a ...

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. Donald was Regius Professor of Midwifery at the University of Glasgow. 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. 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 The University of Colorado (CU) is a system of public universities in Colorado. It consists of four institutions: University of Colorado Boulder, University of Colorado Colorado Springs, University of Colorado Denver, and the University of Co ...

. 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. 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 2015, a post by a pregnant woman named

Jen Martin Jen is a feminineSebased on U.S. Social Security Records given name, frequently a shortened form (hypocorism) of Jennifer, and occasionally a surname. It may refer to: Given name People * Jen Adams (born 1979), Australian lacrosse coach and form ...

(née Cardinal) and her husband to

YouTube YouTube is a global online video platform, online video sharing and social media, social media platform headquartered in San Bruno, California. It was launched on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim. It is owned by ...

, 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.

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. ammeltoft, Tine, 2007, Sonography and Sociality – Obstetrical Ultrasound Imagining in Urban Vietnam, Medical Anthropology Quarterly, 21:2, 133-153/ref> 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. This “technocratic takeover” 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. 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. 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. 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. 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”. 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”.

References

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
The Global Library of Women's Medicine
Imaging in Obstetrics and Gynecology link {{Authority control Tests during pregnancy Medical ultrasonography Prenatal sex discernment Articles containing video clips