Fetal imaging Flashcards
Which 1 of the following is true concerning fetal magnetic resonance imaging (MRI) for the diagnosis of birth defects?
A. Fetal MRI is superior to ultrasonography for the diagnosis of renal anomalies and should be used as an adjunct to sonography
B. According to ACOG, fetal MRI can be sued as a general screening tool for birth defects
C. The US Food and Drug Administration has established thar MRI is safe in pregnancy
D. In fetuses wiht a central nervous system anomaly identified by ultrasonography, MRI provides additional information in up to 50% of cases
D.
Fetal magnetic resonance imaging (MRI) should not be used as a general screening tool for fetal anomalies. According to the American College of Obstetricians and Gynecologists (ACOG), fetal MRI should only be performed following a targeted ultrasound examination performed by an experienced ultrasonographer. Fetal MRI has been shown to be of benefit in the diagnosis of central nervous system (CNS) anomalies and the assessment of fetal airway compromise in the evaluation of fetal neck masses, micrognathia, cervical neck masses, and tracheoesophageal fistulas. The advantages of ultrafast MRI include the use of multiplanar reconstruction and a large field of view compared with obstetrical ultrasonography. Regarding the safety of MRI in pregnancy, there are no known harmful effects in the developing fetus with field strengths of 1.5T or less. The US Food and Drug Administration states that the safety of fetal MRI “has not been established.” Most centers limit the use of MRI until the second trimester and require informed consent from the patient. In fetuses with suspected CNS anomalies detected by ultrasound, MRI confirmed the ultrasound findings in 65% of the fetuses and provided additional information in 22.1–50%, depending on the study. In a study by Levine, MRI for CNS anomalies provided additional information in 50% of cases and discovered a new finding in 32%. MRI imaging of monochorionic multiple gestation complicated by intrauterine fetal demise (IUFD) or severe twin-to-twin transfusion syndrome may assist in counseling for subsequent neurologic outcomes. MRI can diagnose multicystic encephalomalacia, a devastating neurologic disorder that can be found in up to 20% of monochorionic twins with an IUFD. Ultrasound imaging of the fetal urinary tract remains excellent and is not improved on by MRI; however, in select cases of obstructive uropathy and renal tumors, it may be of assistance.
US ObGyn 2014; 44: 388-393.
Levine et al, Fetal CNS anomalies: MRI augments sonographic diagnosis, Radiology 2003a;229:51-61.
Fetology, Diagnosis and Management of the Fetal Patient; 2nd ed, 2010, pp 6-9.
Fetal Imaging: Executive Summary of a Joint Eunice Kennedy Shriver National Institute of child Health and Human Development, SMFM, AIUM, ACOG, ACR, SPR, SRUFIW. AJOG 2014; 123(5) 387-397
Redating a pregnancy based on US differences?
In pregnancies that result from assisted reproductive technology (ART), ART-derived age should be used to assign EDD. As soon as data from the LMP, the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record. Subsequent changes to the EDD should be reserved for rare circumstances, discussed with the patient, and documented clearly in the medical record. The pregnancy EDD should be changed based on ultrasound assessment if the discrepancy is: More than 5 days at less than 8 6/7 weeks, More than 7 days between 9 and 13 6/7 weeks based on crown rump length (CRL), More than 7 days between 14 and 15 6/7 weeks based on biometry, More than 10 days between 16 and 21 6/7 weeks based on biometry, More than 14 days between 22 and 27 6/7 weeks based on biometry, More than 21 days at 28 weeks and beyond based on biometry. Date changes for smaller discrepancies are appropriate based on how early within these ranges the ultrasound examination was performed and on clinician assessment.
Which of the following is a condition that is associated with oligohydramnios?
A. Cleft lip/palate
B. Renal agenesis
C. Congenital pulmonary airway malformation
D. Tracheo-esophageal fistula
B.
Oligohydramnios is a condition in which the amniotic fluid is decreased, defined as an amniotic fluid index (AFI) < 5 cm, AFI < 5% for the gestational age or maximal deepest pocket < 2 cm.
While there are many causes of oligohydramnios including placental insufficiency and preterm premature rupture of membranes (PPROM), anatomic etiologies of oligohydramnios include conditions that impair fetal urine excretion, such as GU obstruction or and renal agenesis. Tracheo-esophageal fistula, congenital pulmonary airway malformation, and cleft lip/palate are anomalies that may affect fetal swallowing. Thus, these entities may be associated with polyhydramnios, not oligohydramnios.
33-year-old G3P2002 at 21 weeks of gestation presents to your office for a consultation as a vasa previa was suspected on her outside ultrasound. You perform an ultrasound and confirm fetal vessels within 2 centimeters of the cervical os that display a heart rate of 156 beats per minute when a transvaginal ultrasound with pulsed color Doppler is performed. She read about hospitalization for vasa previa on the internet and wants to know when she will be admitted because she needs to coordinate care for her 3- and 6-year-old children at home. You explain to the patient that provided she remains asymptomatic and does not have any vaginal bleeding, you recommend:
A. No hospitalization
B. Hospitalization from now until delivery.
C. Hospitalization from viability until delivery.
D. Hospitalization from 28 weeks gestation until delivery.
E. Hospitalization from 30 weeks gestation until delivery.
E.
The SMFM guidelines on the diagnosis and management of vasa previa recommend consideration of antenatal hospitalization for women with a prenatal diagnosis of vasa previa from 30 – 34 weeks gestation with a scheduled cesarean section from 34 – 37 weeks gestation. Provided this patient does not have regular contractions or bleeding prior to 30 weeks gestation, antepartum admission can be planned for 30 weeks gestation. If she notices any bleeding or regular contractions prior to her planned admission, she should immediately present for evaluation.
Given the risk-benefit profile of antenatal corticosteroids, if indications do not develop earlier, it is reasonable to consider treatment at 28-32 weeks of gestation in case of need for urgent preterm delivery.
A 25-year-old G1 at 19 weeks 2 days of gestation presents for a routine anatomic survey. You diagnose this patient with a low-lying placenta. When do you instruct her to return for a follow-up ultrasound?
A. No further ultrasounds are indicated.
B. Follow up every 4 weeks to assess placental location.
C. Follow up at 28 weeks to assess placental location.
D. Follow up at 32 weeks to assess placental location.
E. Follow up at 36 weeks to assess placental location.
D.
In 2015 the Society for Maternal-Fetal Medicine published a consensus on the diagnosis and management of vasa previa. An algorithm for the diagnosis of vasa previa recommends that for women with a placenta previa or low-lying placenta (the latter defined as a placental edge that does not reach the internal cervical os but is ≤ 20 mm from the os) diagnosed at a routine midtrimester ultrasound, a follow-up ultrasound should be performed at 32 weeks gestation. This follow up should include a transvaginal ultrasound with color to rule out a vasa previa. If a vasa previa is suspected, pulsed color Doppler should be used to confirm the diagnosis. For the patient in this question, option D follows the guidelines published by the Society for Maternal-Fetal Medicine.
Which definition of oligohydramnios should be used based on available evidence?
A. AFI of 5 cm or less
B. Absence of a 2 cm x 2 cm pocket
C. Absence of a 2 cm x 1 cm pocket
D. All of the above are appropriate, but in your practice you should have a single, uniform definition.
E. Follow up at 36 weeks to assess placental location.
C.
As noted in question one, oligohydramnios may be defined three ways, including an amniotic fluid index (AFI) < 5 cm, AFI < 5% for the gestational age or maximal deepest pocket < 2 cm. The best available evidence supports the use of the maximal deepest pocket method (should be at least 1 cm in diameter) as it minimizes interventions without increasing the risk of adverse perinatal outcomes. To obtain the most accurate assessment of the amniotic fluid volume, it is important to adhere to the following technical considerations: 1) measurement in the maternal sagittal plane without angling of the transducer, 2) adjustment of ultrasound gain to allow visualization of the umbilical cord, and 3) measurement of selected amniotic fluid pockets should be free of fetal parts and umbilical cord. Narrow amniotic fluid pockets or those within 1 cm of fetal parts should not be measured.
Which of the following is not an accepted definition of umbilical vein varix found on ultrasound?
A. Dilation of greater than or equal to 9mm
B. Dilation greater than 2SD above the mean for gestational age
C. Turbulent flow visualized on Doppler assessment of the umbilical vein
D. Dilated portion is at least 50% wider than the non-dilated portion
C.
This is not a component of the accepted criteria for definition of this condition on fetal ultrasound. The remaining answer choices are all acceptable methods for diagnosis of fetal umbilical vein varix.
How common are co-existing anomalies in cases of umbilical vein varix diagnosed by prenatal ultrasound?
A. 19%
B. 31%
C. 4%
D. 57%
E. 71%
A.
The correct answer is 19%, which was reported in a meta-analysis of over 250 cases of FIUVV. The additional anomalies included mild aortic stenosis, other congenital cardiac abnormalities, SGA, trisomy 21, and 22q deletion.
Which of the following is not associated with the finding of fetal umbilical vein varix on prenatal ultrasound?
A. Thrombosis of the umbilical vein
B. SGA
C. Trisomy 21
D. Intrauterine fetal demise
E. Renal anomalies
E.
Although multiple case reports and case series have been published on this topic, as well as a meta-analysis published in 2018, there is no clear consensus as to the rate of fetal demise associated with this condition. In the meta-analysis by Di Pasquo et al, the cases of fetal demise were limited to fetuses with co-existing anatomic or genetic abnormalities; the two most common genetic changes in fetuses with FIUVV were trisomy 21 and 22q11.1 deletion. There is an association between FIUVV and small for gestational age across multiple studies. Of the proposed causes of fetal demise attributed (spelling-attributed) to FIUVV, one is thrombosis of the umbilical vein, and the other is possible heart failure due to increased preload.
Di Pasquo E, Kuleva M, O’Gorman N, Ville Y, Salomon J. Fetal Intra-abdominal umbilical vein varix: retrospective cohort study and systematic review and meta-analysis. Ultrasound Obstet Gynecol 2018;51:580-585.
