If you have an ultrasound examination in your doctor's office, or with a radiologist, or other physician, the following are the minimum guidelines that should be met. These guidelines have been published not only by the American Institute of Ultrasound in Medicine, but also by the American College of Radiology (2003), and the American College of Obstetricians and Gynecologists (2004). The following are the guidelines that should be followed when performing a routine screening or Standard examination of the fetus.

Imaging Parameters for a Standard Fetal Examination

 Fetal cardiac activity, number, and presentation should be reported.

Abnormal heart rate and/or rhythm should be reported. Multiple pregnancies require the documentation of additional information: chorionicity, amnionicity, comparison of fetal sizes, estimation of amniotic fluid volume (increased, decreased, or normal) on each side of the membrane, and fetal genitalia (when visualized).

A qualitative or semiquantitative estimate of amniotic fluid should be reported.

Although it is acceptable for experienced examiners to qualitatively estimate amniotic fluid volume, semiquantitative methods have been described for this purpose (eg, amniotic fluid index, single deepest pocket, 2-diameter pocket).

The placental location, appearance, and relationship to the internal cervical os should recorded. The umbilical cord should be imaged, and the number  of vessels in the cord should be evaluated when possible.

This illustrates the cervix and the locatio of the anterior placenta.

 It is recognized that apparent placental position early in pregnancy may not correlate well with location at the time of delivery. Transabdominal, transperineal, or transvaginal views may helpful in visualizing the internal cervical os and its relationship to the placenta. Transvaginal or transperineal ultrasound may be considered the cervix appears shortened the patient complains of regular uterine contractions.

Gestational Age Assessment

First-Trimester Crown-Rump Measurement This the most accurate means for sonographic dating of pregnancy. Beyond this period, a variety of sonographic parameters, such as biparietal diameter, abdominal circumference, and femoral diaphysis length, can be used to estimate gestational age. The variability of gestational age estimations, however, increases with advancing pregnancy. Significant discrepancies between gestational age and fetal measurements may suggest the possibility of fetal growth abnormality, intrauterine growth restriction, or macrosomia.

Head Circumference This measured at the same level as the biparietal diameter, around the outer perimeter of the calvarium. This measurement is not affected by head shape.

Femoral Diaphysis Length This can be reliably used after 14 weeks’ gestational age. The long axis of the femur shaft is most accurately measured with the beam of insonation being perpendicular to the shaft, excluding the distal femoral epiphysis.

Abdominal Circumference This  should be determined at the skin line on a true transverse view at the level of the junction of the umbilical vein, portal sinus, and fetal stomach, when visible. The abdominal circumference measurement is used with other biometric parameters to estimate fetal weight and may allow detection of intrauterine growth restriction or macrosomia.

Fetal Weight Estimation

Fetal weight can be estimated by obtaining measurements, such as the biparietal diameter, head circumference, abdominal circumference, and femoral diaphysis length. Results from various prediction models can be compared to fetal weight percentiles from published nomograms. If previous studies have been performed, interval measurement changes should also be evaluated for growth. Scans for growth evaluation typically can be performed at least 3 weeks apart. A shorter scan interval may result in confusion as to whether anatomic changes truly are due to growth as opposed to variations in the measurement technique itself. Currently, even the best fetal weight prediction methods can yield errors as high as ±15%. This variability can be influenced by factors such as the nature of the patient population, the number and types of anatomic parameters being measured, technical factors that affect the resolution of ultrasound images, and the weight range being studied.

Fetal Anatomic Survey

Fetal anatomy, as described in this document, may adequately be assessed by ultrasound after approximately 18 weeks’ gestational age. It may be possible to document normal structures before this time, although some structures can be difficult to visualize due to fetal size, position, movement, abdominal scars, and increased maternal wall thickness. A second- or third-trimester scan may pose technical limitations for an anatomic evaluation due to imaging artifacts from acoustic shadowing. When this occurs, the report of the sonographic examination should document the nature of this technical limitation. A follow-up examination may be helpful. The following areas of assessment represent the essential elements of a standard examination of fetal anatomy. A more detailed fetal anatomic examination may be necessary if an abnormality or suspected abnormality is found on the Standard Examination.

Head and neck Cerebellum Choroid plexus Cisterna magna Lateral cerebral ventricles Midline falx Cavum septi pellucidi
Chest The basic cardiac examination includes a 4-chamber view of the fetal heart. If technically feasible, an extended basic cardiac examination can also be attempted to evaluate both outflow tracts.
Abdomen Stomach (presence, size, and situs) Kidneys Bladder
Umbilical cord insertion site into the fetal abdomen Umbilical cord vessel number
Spine Cervical, thoracic, lumbar, and sacral spine
Extremities Legs and arms (presence or absence)
Gender Medically indicated in low-risk pregnancies only for evaluation of multiple gestations.
Anatomy Not Included in the Standard Examination The following are examples of fetal anatomy not included in the Standard Examination. For this reason the Standard Examination is not a comprehensive study of the fetus.
This is an image of the mouth, lips, and nostrils. This view is one that is used to screen for cleft lip This is an image of the profile of the face that includes the nasal bone. Abnormal facial profiles may be associated with genetic syndromes.
The image on the left illustrates the diaphragm that separates the lungs and heart from the abdomen. If a diaphragmatic hernia is present, this could be life threatening in the immediate newborn period. The image on the left illustrates the aortic arch.
The image on the left is a normal uterine artery Doppler waveform. The image on the right is an abnormal uterine artery Doppler waveform which is associated with an increased risk for pre-eclampsia, poor growth of the fetus, and pre-term delivery.
These are image of the fetal face obtained at 20 and 26 weeks of pregnancy.
This is a 3D image of the fetal skeleton. The left image shows the bones of the side of the skull, the image on the right the spine and ribs.
This is a recording of the umbilical artery illustrating absent flow. This was identified at 23 weeks with normal amniotic fluid. This patient was hospitalized for monitoring because of the risk for fetal death. The image on the right is from the same fetus showing normal amniotic fluid. Some physicians only would perform a Doppler study if there was low amniotic fluid or a small fetus.
The image on the left is the four-chamber view of the heart. The ventricular septal defect, which is a hole in the wall (VSD) separating the ventricular chambers is difficult to see with B-mode ultrasound. The image on the right shows the blood crossing the ventricular septum. RA=right atrium, LA=left atrium, RV=right ventricle, LV=left ventricle.