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Diagnostic Ultrasound

• Editor's Note
• List of Articles

List of Articles

• First Trimester Ultrasound Applications
  For at least 20 years, many researchers have advocated the use of ultrasound in general and transvaginal ultrasound in particular to identify anomalies in the first and early second trimester. Over that period, advances in transducer technology, faster computers, and deepening understanding of developmental anatomy have facilitated such use. Increasing reliance on first-trimester screening brings more and more women with gestations from 11 to 14 weeks to the obstetrician’s office, providing an opportunity to expand the narrow viewing angle of the ultrasound probe from the nuchal area to the entire fetus. As time goes on, we may discover additional compelling reasons to shift the first fetal evaluation from the second-trimester to the first-trimester. In the meantime, we find no reason not to widen the viewing angle of transducer probes to assess fetal anatomy at the first-trimester scan. This document discusses evolving applications of first-trimester ultrasound. Scanning can be performed transvaginally or transabdominally, although the transvaginal route is preferred during the first-trimester, because of high-resolution images it yields. Clear images improve reliability and accuracy. However, at times, a combination of transvaginal and transabdominal scanning may be preferred. Both basic and advanced first-trimester ultrasound applications are discussed in this review.
  
  
• Doppler Ultrasonography in Obstetrics
  The advent of sonography has changed the practice of obstetrics by providing a window to the womb through which the anatomic structure of the fetus can be evaluated. The addition of Doppler flow studies of maternal and fetal vessels has provided a tool where the physiology of the maternal-fetal unit can be assessed. This information can provide the physician and the patient with vital information for a subsequent approach to the pregnancy. The use of fetal Doppler blood flow studies has become common in the evaluation and management of pregnancies complicated by conditions such as suspected fetal growth restriction and red blood cell isoimmunization to guide intrauterine therapy and delivery. The most commonly assessed Doppler flow studies of the fetus are the umbilical artery and middle cerebral artery (MCA). Doppler flow studies of MCA are used in the assessment of the fetus at risk of anemia and growth restricted fetus.
  
  
• Ultrasound Screening of Neural Tube Defects
  The prevalence of congenital anomalies of the central nervous system varies in different epidemiologic studies, mostly as a consequence of the type of ascertainment and the length of follow up. The clinical role of sonographic biometry of the fetal cranium is well established. Biparietal diameter, head circumference, and transverse cerebellar diameter are currently used for assessing gestational age and fetal growth and identifying cranial abnormalities. Anencephaly and spina bifida comprise the majority of neural tube defects. In the 20 plus years since maternal serum alpha-fetoprotein (MSAFP) was recommended in United States for the general population, significant changes in the use of ultrasound and better understanding of the factors that place a woman at increased risk of bearing a child with spina bifida (and thus a candidate for diagnostic testing and not screening) have changed the utility of MSAFP screening. Amniotic fluid evaluation of alpha-fetoprotein and the role of fetal surgery for neural tube defects (NTDs) are also discussed.
  
  
• Ultrasound Evaluation of Uterine Scar
  Between 1996 and 2003 the cesarean delivery rate in the United States increased dramatically from21.2% to 27.1%. Over the same interval vaginal birth after cesarean birth (VBAC) has decreased from 28.3% to 10.6%. This decrease may be attributed to concerns regarding the risks during trial of labor, such as uterine rupture, estimated to occur in 0.3-4.0% of pregnancies with history of cesarean delivery. As the VBAC rate increased, so did the number of well-publicized reports of uterine rupture and other complications during trials of labor after previous cesarean deliveries. As a result, many physicians and hospitals have discontinued the practice altogether. This abrupt change in practice has contributed to the cesarean delivery rate in the United States increasing again, reaching an all-time high of 26.1% in 2002, while the VBAC rate has decreased by 55% to 12.6%. The risk for poor obstetric outcome in a subsequent pregnancy has been shown to be related to surgical technique, with classical cesarean delivery having the highest risk for rupture and lower segment incisions having a lower risk. Clinical significance of uterine scar dehiscence in women with previous cesarean delivery is also discussed.
  
  

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