The role of ultrasound in obstetrics has seen rapid changes since its inception. Ultrasound can play a part in detecting something as simple as the sex of a fetus or as complex as the fetal effects of a maternal condition such as hypertension.
Exploring ultrasound's genesis can help reveal how it has been used to enhance maternal care and alter the way obstetrics is practiced.
The History of Ultrasound
Although ultrasound is relatively new as a diagnostic device, the technology itself is older, and clinical uptake lags behind each advance. Interestingly, the foundations of ultrasound are not located in medicine but in the nautical industry. One of the best explanations of the beginnings of ultrasound was described in the journal Rheumatology in 2004 — an Italian physiologist who experimented with bats in the 1700s determined that they were able to fly and hunt by night because they navigated by sound and not sight. Bats could fly without bumping into objects if their eyes were covered but not if their mouths were covered. He postulated that they produced sounds that humans cannot hear and used these sounds to navigate in a process called echolocation.
Building on this theory, sonar technology saw advancements in the early 1900s for use in the nautical industry. World War I brought demands for protection against enemy submarines, and ultrasound was born. Ultrasound expanded from nautical to military to industrial use — employed to detect flaws in metal and welds — before eventually finding applications in medicine.
Ultrasound was first used in medicine in the 1940s in an attempt to detect brain tumors. Within 15 years, researchers had begun investigating A-mode and B-mode as well as introducing transducers for transrectal and transvaginal use. The first paper describing the use of ultrasound to resolve a differential diagnosis (a simple ovarian cyst) was published in the Lancet in 1958; only a few short years later, the same obstetrician diagnosed placental previa — an early gestation — and developed a method of measuring the fetal head biparietal diameter.
How Ultrasound Has Advanced
Fast forward to the 21st century: Although the original ultrasound modes are still in use, technological advances have pushed the technique of echolocation down new diagnostic avenues. Not only can clinicians see inside the body better than ever, but it's also possible to see dimensional structures, track movement and measure blood flow and velocity.
CME Science places several ultrasound advances in the 1970s, including continuous wave, spectral wave and color Doppler. This decade also introduced the technique of ultrasound-guided amniocentesis. Articles reporting on the utility of fetal nuchal translucency thickness began appearing in the literature around 1994.
CME Science places 3D ultrasound in the 1980s. When 4D was introduced in the 1990s, it added video capabilities to ultrasound by combining multiple images. The most advanced ultrasound at the moment utilizes 5D features, which capture high-definition images and live images that show the fetus in better resolution.
Ultrasound Advancements With the Most Impact
A Cochrane Database Systematic Review found that most fetal deaths had a known cause. Some of these include maternal conditions such as diabetes and hypertension, while others are related to fetal conditions including intrauterine growth restriction, congenital disorders or placental problems.
The clinical advent of ultrasound provided a way to monitor these conditions. Health Services Research found that the use of ultrasound achieved a nearly 20% decline in fetal deaths in Norway. The same authors, whose results were published in the International Journal of Epidemiology, found an even greater reduction in fetal deaths with the implementation of fetal Doppler.
The journal Ultrasonography points to Doppler ultrasound as one of the most clinically useful diagnostic tools in obstetrics. It can play a role in a variety of investigations, including umbilical artery flow, studies of the fetal vessels and heart, the uterine artery and other maternal vessels.
Fetal Medicine writes that color Doppler is useful in evaluating not only the fetal vessels of the heart, placenta, umbilical cord, kidneys and intracranial vessels but also in investigating fetal tumors and resolving a differential diagnosis of oligohydramnios.
The Evolving Role of Ultrasound in Obstetrics
As ubiquitous as ultrasound currently is within OB/GYN, it can be easy to forget that its utility has been realized only rather recently. In fact, OB/GYNs who have recently begun practicing after residency may be among the first babies whose sex was determined in utero by ultrasound.
In 1987, the American Journal of Obstetrics and Gynecology published an article entitled "Can Ultrasonography Replace Amniocentesis in Fetal Gender Determination During the Early Second Trimester?" The study found a 92.7% determination rate.
Ultrasound has enabled the detection of congenital abnormalities before birth, supported determinations of gestational age and fetal growth and allowed the discovery of conditions in the maternal environment that could otherwise lead to poor outcomes or death. More advanced ultrasound technology such as 3D imaging paired with advanced use of Doppler has pushed clinicians' capacity to perform evaluations into the first trimester, allowing obstetricians the earliest insight into fetal health. In many cases, ultrasound has the ability to eliminate the need for more invasive testing during efforts to rule out fetal and maternal conditions. From origins that in many ways still feel fresh, ultrasound has laid a solid foundation for even broader value with future advancements.
