Sonographic examination with the appropriate indication is an appropriate skill that enhances the diagnostic and therapeutic capabilities of family physicians who practice obstetrics. Even physicians who do not deliver babies are faced with clinical questions for which diagnostic ultrasound is indicated. Studies do not support the routine use of sonography in low-risk prenatal care; however, societal expectations and the relative ease of access to this technology have made it an established aspect of obstetric care. The Radius study group evaluated the use of screening ultrasounds in 15,151 low-risk pregnancies and found no difference in perinatal mortality, birth weight, or preterm birth. The study did not evaluate its use in high-risk pregnancy (Ewigman et al., 1993).
Box 21-12 Indications for Obstetric Ultrasound
1. Determination of gestational age
• Suspected miscarriage or fetal demise
• Vaginal bleeding
• Suspected multiple gestation
• Suspected hydatidiform mole
• Suspected ectopic pregnancy
• Size-date discrepancy
• Uterine or pelvic mass or abnormality
• Congenital anomalies
• Fetal presentation
3. Antenatal monitoring a. Biophysical profile (BPP)
b. Intrauterine growth retardation (IUGR)
c. Fetal macrosomia
4. Adjunct to obstetric procedures
• Chorionic villus sampling
• Cephalic version
5. ACOG* recommends ultrasound at 18 weeks for all patients.
• Confirm dates and fetal survey.
From http://www.fpnotebook.com/OB/Rad/ObstrcUltrsnd.htm. *American College of Gynecologists and Obstetricians.
The obstetric ultrasound has numerous indications and benefits in prenatal care (Box 21-12). Benefits include estimation of fetal age through biometry (accurate to within 1 week under 20 weeks, ±2 weeks at 20-28 weeks, and ±4 weeks after 28 weeks). In the hands of an experienced sonog-rapher, the gestational sac size or the crown-rump length has proved a reliable measure of gestational age (Fig 21-18). Again, early ultrasound may provide more accurate dating, which is important for timing screening tests and interventions and for optimal management of complications such as post-term pregnancies (Neilson, 2004). Prenatal diagnosis and evaluation of fetal anomalies, growth anomalies (e.g., size vs. date discrepancies), fetal assessment (e.g., BPP, confirmation of fetal demise), maternal factors (e.g., diagnosis of ectopic pregnancy), and uterine anomalies are other indications and benefits.
The overutilization or recreational use of ultrasound technology may pose a medical-legal risk, particularly in the hands of an inexperienced provider.
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