Ultrasonography represents the most significant advance in obstetric diagnosis and clinical management in the past 40 years. Ultrasonography in pregnancy is a simple, painless and harmless examination used in everyday practice for the present diagnosis.
The largest risk of antenatal sonography is probably misdiagnosis. A false positive diagnosis of a malformation may lead to parental anxiety and these errors can be corrected by a second examination in a tertiary referral center. A missed diagnosis (false negative) remains undetected unless the patients undergoes for a second examination for another indication. These limitations are often gestational age dependent. But if a significant congenital anomaly is recognised at delivery one of the patients question is: «Could we have seen this on ultrasound before delivery?». Obstetrics sonography should be performed at an appropriate gestational age by an experienced practitioner.
The ACOG and the AIUM have published guidelines for the basic ultrasound examination in pregnancy. This basic examination is performed most often for the purpose of biometry and the establishment of gestational age. Various descriptive terms have been used to identify such a detailed study including level II comprehensive, extended and targeted.
This targeted study is performed for the detection of fetal anomalies in women at risk for having a malformed fetus. The pregnant patient expects to have information about baby's health and in case a congenital anomaly is present she wants to kwon the prognosis, the treatment and the recovery.
Routine use of ultrasound in low pregnancies has been offered for the decrease of labour inductions performed for postdatism, for the early detection of multifetal gestations, for detection of placental implantation abnormalities and for the antenatal diagnosis of congenital anomalies.
There is good evidence to support the recommendation that the sensitivity of the ultrasound screening in detecting fetal malformations in low risk pregnancies cannot be established with precision it will continue to be decided on a local level and varies in different centers with different level of operators training and financial resources.
Sonography for fetal biometry and when precise estimation of gestational age is required (in cases such as planning a caesarean delivery), should be performed in the first trimester or as early in pregnancy as feasible.
Eighteen to 20 weeks is the traditional and appropriate time to perform a targeted scan. This ultrasound study allows a detailed review of fetal anatomy and is early enough so that amniocentesis or other diagnostic procedures can be performed prior to fetal viability.
The genetic sonogram is a targeted study with special emphasis on ultrasonographic markers that may indicate aneuploidy.
Targeted ultrasonography at 18-20 weeks allows the couple to consider all of their options and allows for appropriate referral and counselling.
However some malformations are not easily visualised at this period. Hydrocephalus, bowel atresias may develop after this period and may not be demonstrable until after 24 week's gestation while the optimal time for fetal echocardiography is probably somewhat later (20-22 weeks).
Antenatal sonography is performed in different medical centers, doctor's offices, hospitals, by physicians of varying levels of experience or by technicians.
If a physician is unable to document formal residency, fellowship, or other postgraduate training, he or she must have completed 100 hours of American Medical Association category 1 continuing medical education in diagnostic ultrasound, with evidence of involvement at least 500 diagnostic examinations under the supervision of a qualified physician.
The experience of the obstetrician clinician with sonography must begin with detailed knowledge regarding fetal cross sectional anatomy. It is important for the clinician to know his or her limits with regard to the use of ultrasound.
Limitations of obstetrical ultrasonography should be briefly reviewed with patients prior to the initiation of the procedure. Some major malformations are easily detectable whereas other malformations present subtle ultrasound images, and may not be diagnosable in the midtrimester.
Ultrasound is used not only for diagnosis but as a tool for the management of a complicated pregnancy and for this reason the perinatologist is perfectly the right doctor to provide sonographic diagnosis and plan the management of a high risk pregnancy.
The issue of routine sonography for low risk pregnant women continues to be contentions even though, randomized trials have not been able to demonstrate a clear benefit. Although great progress is being made in the first trimester diagnoses of congenital anomalies, most targeted studies are performed at 18-20 weeks of gestation.
The highest rates of detection of congenital anomalies are seen in tertiary care settings such as a university medical center.
In high risk cases a counsulting perinatologist is commonly the physician most likely to integrate the ultrasound findings.