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DESCRIPTIONultrasound in obstetrics
Principles and Applications of Ultrasound to ObstetricsHonor M. Wolfe
I:Danie Catoe/Honor/PowerPt/Chap13 GenPrinc&Appl USonography.ppt
What is the accuracy of ultrasound in the assessment of gestational age?
Accuracy 1/Gestational Age
Gestational age accuracy
1st trimester + 1 week2nd trimester + 2 weeks3rd trimester + 3 weeks
First Trimester: CRL
5-12 weeks gestation< 10 wks + 3-5 days> 10 wksless accuratevariable position/flexion5-7 days
2nd and 3rd trimester
Accuracy of GA estimates increases as more variables are measured.
- Composite estimate of:Biparietal diameterHead circumferenceFemur lengthAbdominal circumference
Does maternal BMI impact ultrasound and if so how and why?
PhysicsHigh frequency sound waves> 20,000 cycles/second
FrequencyNumber of waves per unit timeExpressed as hertz (Hz)
Diagnostic ultrasound2-10 million Hz (2-10 MHz)
PhysicsFrequencyInversely proportional to penetrationDirectly proportional to resolution
ProbesTransabdominal 3.5, 5, 7 mHzTransvaginal 8-9 mHz
Sound waves- Transducer both sends and receives - Reflected by emitting transducer- Image displayed as: 1. Brightness - intensity of echo 2. Time lag - distance
Ultrasound and BMIHeavier patients Need more penetration (lower mHz)Get less resolution (lower mHz)
What are the types of US who gets what type of scan?
Basic UltrasoundExaminationFetal number/presentation/lifePlacental locationAssessment of AFVAssessment of gestational ageSurvey for gross malformationsEvaluation for maternal pelvic massesMetric examinationScreening
Assessment of AFV, BPPGuidance for AmniocentesisExternal cephalic versionConfirmation of fetal deathPlacental localization (hemorrhage)Fetal presentation
Comprehensive UltrasoundIndicationsSuspicion of anomalous fetusHistoryClinical evaluationPrevious ultrasoundDetailed assessment of fetal anatomyColor/power dopplerArterial/venous doppler
What type of anomalies is this patient at risk for and how good is ultrasound at finding them?
How good is ultrasound at finding anomalies?
It depends on:
The anomaly Minor anomalies, heart anomalies hardestWhen we lookWhen apparent, 20 24 wks optimal for mostWho we are looking at Thinner, normal amniotic fluid volumeAnd.Who is looking.
Directly proportional to severity of anomaly - 89% lethal anomalies - 77% requiring NICU admission - 30% minor anomalies
Cardiovascular defectsCleft up / palateMicrocephalus
Types of Ultrasound what might be missed?Basic (76805)Measurements, AFI, placentaHeadHeart (not color)AbdomenComprehensive (76811)Face, profileExtremitiesHeartColor dopplerExtremities
What about antenatal testing?
Table 43-1. COMPONENTS AND THEIR SCORES OF THE BIOPHYSICAL PROFILE Variable Score 2 Score 0 Fetal breathing The presence of at least 30 sec of sustained fetalmovements breathing movements in 30 min of observationLess than 30 sec of fetal breathing movements in 30 min
Fetal movements Three or more gross body movements in 30 min of Two or less gross body movement observation: simultaneous limb and trunk movements in 30 min of observationFetal tone At least one episode of motion of a limb from position Fetus in position of semi- or of flexion to extension and rapid return to flexionS full-limb extension with no return or slow return to flexion with movement; absence of fetal movement counted as absent tone.
Fetal reactivity Two or more fetal heart rate accelerations of least No acceleration or less than 15 beats/min and lasting at least 15 sec and associated two accelerations of fetal with fetal movement in 20 min heart rate in 20 min of observation
Qualitative amnionic Pocket of amnionic fluid that measures at least 1 cm Largest pocket of amnionic fluid fluid volume in two perpendicular planes measures< 1 cm in two perpendicular planesFrom Manning and colleagues (1985), with permission.
How well do we estimate fetal weight?
Estimated Fetal WeightVarious formulasAll involve the abdominal circumferenceAlso Femur length, head circumference and/or BPDLess Accurate in bigger babies (> 4000 grams)Accuracy + 10 15%Term harder to get measurementsFetal position AFI
Figure 1 (No legend p 524 OB Gyn 1999: 93: 523-6) put in author and year
RED CELL ALLOIMMUNIZATIONFrequency of Irregular Antibodies% D Kell Duffy MNS Kidd LutheranQueenan et al. Obstet Gynecol 1969; 34: 767-70Geifman-Holtzman et al. Obstet Gynecol 1997; 89: 272-5
ACOG recommends antenatal RHIGACOG recommendsantenatal RHIG
RED CELL ALLOIMMUNIZATIONRhesus Prophylaxis66% of Rhesus cases antepartum sensitization13% of cases inadvertent omission of RhIGHughes et al. Brit J Obstet Gynaecol 1994; 101:297-300
RED CELL ALLOIMMUNIZATIONNew Onset RhD SensitizationFollow maternal titers every 2 - 4 weeks until critical value reached (32 at UNC) Determine paternal genotype for involved antigen
RED CELL ALLOIMMUNIZATIONNew Onset RhD SensitizationPaternal genotype = heterozygous (55%); do amniocentesis for fetal blood typingPaternal genotype = homozygous (45%) or affected fetus by amniocentesis DNA testing; begin serial amniocenteses for OD450 testing
RED CELL ALLOIMMUNIZATIONPrevious RhD SensitizationHistory of previous IUFD, intrauterine transfusions or neonatal exchange transfusions Maternal titers not helpful