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Role of Magnetic Resonance Imaging in Obstetrics

Summary of Key Points Magnetic resonance imaging (MRI) does not use ionizing radiation, and no known biologic risks are associated with this imaging modality. MRI is an important tool for the evaluation of maternal complications in pregnancy, including the evaluation of atypical advanced ectopic pregnancies, suspected appendicitis, pelvic masses, hepatic and genitourinary diseases, and placenta accreta. In the fetus, MRI is a useful adjunct to the…

Role of Doppler Sonography in Obstetrics

Summary of Key Points Absent or reverse flow during diastole in the umbilical artery represents an advanced stage of placental compromise and is associated with more than 70% of placental arterial obliteration. In the presence of fetal hypoxemia, central redistribution of blood flow occurs, resulting in an increased blood flow to the brain, heart, and adrenals and a reduction in flow to the peripheral and placental…

Antepartum Fetal Surveillance and the Role of Ultrasound

Summary of Key Points The goal of antepartum testing is to prevent fetal death. Antepartum testing is most commonly performed in pregnancies identified as high risk due to maternal conditions or following the identification of fetuses at risk for intrauterine compromise so that intervention and timely delivery can prevent progression to stillbirth. Antepartum surveillance may also be used to confirm the well-being of the normal fetus…

Amniotic Fluid Volume in Fetal Health and Disease

Summary of Key Points The pathways influencing amniotic fluid volume (AFV) are dynamic and complex and are not completely understood. The balance of maintaining the overall AFV occurs at three key areas: fetal urine production and fetal swallowing, the intramembranous pathway, and the osmotic fluid gradient created between the mother and the fetus. There are several published curves that attempt to define a normal AFV. Abnormal…

Ultrasound Evaluation of the Placenta, Membranes, and Umbilical Cord

Summary of Key Points Assessment of the relationship between the placenta and the internal cervical os is an essential component of sonography in the second and third trimesters. Placenta previa is identified in 1% to 5% of second-trimester sonograms but is present at birth in only 3/1000 births. Transvaginal sonography is considered safe regardless of placental location, even in the presence of bleeding. Conditions associated with…

Ultrasound Evaluation of the Gravid Cervix

Summary of Key Points Transvaginal ultrasound (TVU) for cervical assessment is one of the best techniques for predicting preterm birth (PTB). A cervical length (CL) of less than 25 mm between 16 and 24 weeks' gestation is the most reliable threshold for an increased risk of PTB. The shorter the cervix and the earlier in gestation the shortening occurs, the higher the risk of PTB. TVU is…

Evaluation of Hydrops Fetalis

Summary Key Points Diagnosis of hydrops fetalis requires two or more of the following sonographic abnormalities: scalp and body wall edema (defined as skin thickness >5 mm), ascites, pleural effusion, pericardial effusion, polyhydramnios, and placental thickening (≥4 cm in the second trimester and ≥6 cm in the third trimester). Immune hydrops refers to cases in which the underlying condition is due to fetal anemia developing from maternal red blood…

Ultrasound Features of Fetal Syndromes

Summary of Key Points Congenital anomalies can occur in isolation or be indicative of a more extensive underlying process. The presence of a congenital anomaly should prompt a thorough evaluation for other anomalies and consideration of additional advanced fetal imaging. When an underlying global process is suspected, genetic testing is indicated and a geneticist or genetic counselor should be involved. With advances in molecular diagnostics, fetal…

Fetal Genitourinary Tract

Summary of Key Points Normal renal function is fully established by the 9th week of gestation. It is preferable to describe the findings in the fetal renal pelvis, calyces, ureter, and bladder in cases of urinary tract dilation, rather than using nonspecific terms such as pyelectasis, caliectasis, and hydronephrosis. Renal cystic anomalies may be a manifestation of underlying genetic disorders. Ultrasound findings in cases of lower…

Ultrasound Evaluation of the Fetal Gastrointestinal Tract and Abdominal Wall

Summary of Key Points Detection of gastrointestinal tract obstruction is often difficult. Duodenal and small intestinal obstructions are easily visualized, but usually not until the third trimester, whereas esophageal atresia and anal atresia may be difficult to detect at any gestational age. Echogenic small intestine is a nonspecific finding that is associated with an increased risk for Down syndrome, cystic fibrosis, congenital cytomegalovirus (CMV) infection, fetal…

Sonographic Evaluation of the Fetal Heart

Summary of Key Points Prenatal diagnosis of congenital heart disease (CHD) can reduce morbidity and mortality rates by means of delivery and intervention planning. With the proper technology and skill, some forms of fetal cardiac disease can be detected using first trimester and early second trimester sonography. The addition of outflow tracts to the four-chamber view in the standard midtrimester screening examination greatly improves the detection…

Ultrasound Evaluation of the Fetal Thorax

Summary of Key Points The most common chest masses are congenital pulmonary airway malformations (CPAMs) and congenital diaphragmatic hernias (CDHs). For both, the displacement of the heart from its normal position is the most commonly recognized ultrasound finding. CPAMs are unilateral 98% of the time and appear as echogenic areas of the lung, with or without identified cysts. The CPAM volume ratio (CVR) can be used…

Fetal Musculoskeletal System

Summary of Key Points The prevalence of skeletal dysplasias is about 2.4/10,000 births, and 9.1/1000 among perinatal deaths; the most common anomalies are thanatophoric dysplasia, achondroplasia, osteogenesis imperfecta, and achondrogenesis. The new edition of Nosology and Classification of Genetic Skeletal Disorders includes 436 clinical conditions classified into 42 groups involving 364 affected genes; therefore, molecular diagnosis is possible in about 75% of skeletal disorders. Molecular diagnosis…

Ultrasound Evaluation of the Fetal Face and Neck

Summary of Key Points The diagnosis of a typical orofacial cleft involving the palate can be suspected as early as the first trimester by the presence of an anechoic space or discontinuity in the retronasal triangle (RNT) view. Using two-dimensional (2D) ultrasound, identifying typical clefts in the second trimester is best done by utilizing the coronal view of the nose and lips and the axial view…

Ultrasound Evaluation of the Fetal Central Nervous System

Summary of Key Points Central nervous system (CNS) anomalies are among the most frequent malformations encountered by antenatal sonography. Ultrasound allows detection of a large proportion of all CNS malformations in early gestation. However, in some cases the findings may be subtle, whereas in others the anomaly may be progressive and manifest only in late gestation or after birth. Ultrasound will also frequently demonstrate normal anatomic…

Ultrasound Evaluation of Normal Fetal Anatomy

Summary of Key Points Continued advancement of ultrasound technology including increase in frequency and choice of focal position have improved visualization of fetal anatomy and therefore have also increased the required anatomic knowledge of these structures for those performing and interpreting fetal sonograms. Superficial anatomy of the fetus can be delineated with either two-dimensional or three-dimensional sonography and can be useful in confirming normal formation of…

Ultrasound Evaluation in Multiple Gestations

Summary of Key Points Early diagnosis and determination of chorionicity in the first trimester are critical for the optimal management of multiple gestations. Dichorionic twins may be either monozygotic or dizygotic, whereas essentially all monochorionic twins are monozygotic. In addition to risks for aneuploidy and malformations, increased nuchal translucency (NT) in monochorionic twins reflects the potential for complications related to inter-twin anastomoses within a shared placenta.…

Fetal Biometry and Growth

Summary of Key Points In the first trimester, gestational age should be assigned to the pregnancy based on sonographic findings or mean sac diameter prior to the visualization of the embryo and by embryonic or fetal crown-rump length (CRL) thereafter. In the second trimester, gestational age should be assigned based on head measurements that take into account head shape—namely, the corrected biparietal diameter or head circumference…

Evaluation of Fetal Anatomy in the First Trimester

Summary of Key Points Evaluation of fetal anatomy, including a detailed fetal cardiac examination, is possible in the late first trimester. Many anatomic abnormalities can be detected in the first trimester, giving families time to make important decisions regarding pregnancy management and the opportunity for early termination of pregnancy to reduce maternal morbidity risks. Doppler techniques and four-dimensional spatiotemporal image correlation (4D STIC) are modalities used…

Ultrasound of the Early First Trimester

Summary of Key Points The progression of transvaginal sonographic findings in normal early first trimester pregnancies follows a highly predictable pattern, with a gestational age variability of approximately ±0.5 week: gestational sac at 5.0 weeks, yolk sac at 5.5 weeks, embryo with heartbeat at 6.0 weeks, and amnion at 7.0 weeks. In a woman with a positive pregnancy test and no evidence of an intrauterine or…