3 STANDARD: ANTEPARTUM ULTRASOUND
A. Introduction: These guidelines have been developed for use by practitioners performing obstetrical ultrasound studies. In some cases, specialized and/or additional studies may be necessary. While it is not possible to detect all structural congenital anomalies with diagnostic ultrasound, adherence to the following guidelines will maximize the possibility of detecting many fetal abnormalities. A limited examination is acceptable in clinical emergencies but any limited examinations should be documented as such in the medical record.
B. Equipment: The following ultrasound probes are recommended:
(1) Transabdominal scanning: 3 to 5 mHz transducer (probe). For obese patients, 2 to 2.25 mHz transducers may be used;
(2) Transvaginal scanning: 5 mHz or higher transducer.
C. Method: Real time scanning with as low a power setting as possible to obtain the necessary diagnostic information is to be used.
D. Documentation: A record of the examination including a permanent record of the ultrasound images and written report are to be included in the patient's medical record. Any limitation or exclusion of images should be documented in the written report or supplement.
(1) Images to be recorded are outlined in F below as the minimum to be included as part of the record. In cases where an abnormality is suspected, additional images should be recorded if the images more clearly demonstrate the area of suspicion.
(2) Images should be labeled with patient name, date, and site examination. Orientation of the scan may be included if this more clearly demonstrates an abnormal or normal area.
E. Communication:
(1) A written report of the findings should be available to the referring physician within a reasonable time period. This period of time is defined under the following principles with the realization that certain findings may require immediate clinical attention.
(a) Any results which mandate immediate intervention or treatment by the responsible physician necessitate direct and immediate verbal communication between the radiologist and the responsible physician.
(b) Findings of a less urgent nature may be communicated by indirect means such as mail, recorded messages, computer printouts, or FAX. In every instance, the time taken to transfer information shall not unreasonably delay treatment of a condition suspected by antepartum obstetrical ultrasound.
(2) Any limitations of the examination should be described with follow-up studies suggested when appropriate.
F. Examination protocols:
(1) First trimester (The following parameters should be included as a minimum to be analyzed and recorded as part of a standard antepartum obstetrical ultrasound examination. Any abnormalities should be included on the recorded filmed images and be included in the radiology report.)
(a) Gestational sac analysis (to be used when no fetal pole is visualized)
(I) location of sac within uterus
(ii) measurement of sac for estimate of mean sac diameter
(iii) the presence or absence of a yolk sac
(b) Embryo/fetal pole analysis
(i) crown/rump length measurement to be used when visualized for fetal gestational age until the biparietal diameter can be accurately measured.
(ii) biparietal diameter to be used for fetal gestational age in late stages of first trimester when accurate measurement is possible.
(iii) number of embryos present
(c) Fetal viability documentation- The viability of the fetus should be confirmed by real time observation of fetal heart motion. (In general, heart motion can be seen at 7 weeks with transabdominal scanning at 6 weeks with transvaginal scanning.)
(d) Uterine/adnexal analysis includes documenting the following:
(i) uterine wall abnormalities
(ii) cervical abnormalities
(iii) adnexal abnormalities
(2) Second and third trimesters
(a) Fetal viability documentation - Real time observation of fetal cardiac activity and/or fetal motion is necessary for confirmation of viability. Abnormalities of fetal heart rate/rhythm are to be reported.
(b) Fetal presentation/lie - Images and report to document fetal position.
(c) Fetal number if a multiple gestation is present, the following information should be documented:
(i) amniotic membranes (if present)
(ii) number and location of placenta (ae)
(iii) Kid fetal size comparison
(iv) fetal gender (if visualized)
(d) Estimate of amniotic fluid volume (increased, decreased, or normal) should be reported.
(e) Analysis of fetal anatomy includes, but should not be limited to the following:
(i) Abnormalities should be documented on filmed images and reported in the radiology report.
(ii) Analysis of the following regions will detect many structural congenital abnormalities but additional or specialized studies may be necessary. Areas include:
1. cerebral ventricles
2. posterior fossa
3. fetal spine
4. heart
5. stomach
6. renal regions
7. umbilical cord insertion
8. abdominal wall
9. bladder, and
10. limbs.
(f) Analysis of the placenta includes the following:
(i) location and position relative to the internal cervical os appearance
(g) Analysis of the umbilical cord includes the following:
(i) establishing the presence of a three vessel cord if stage of development allows (i.e. early second trimester examinations may be limited as small cord size might not allow for visualization)
(h) Uterine/adnexal evaluation includes documenting the following:
(i) uterine wall abnormalities
(ii) cervical abnormalities
(iii) adnexal abnormalities
G. Assessment of gestational age - In general the most accurate age is based on the earliest study. Gestational age determination from subsequent ultrasound examinations should be compared to the initial ultrasound gestational age.
(1) First trimester gestational age is to be determined by:
(a) mean gestational sac diameter (when no fetal pole is visualized)
(b) crown/rump length (when fetal pole is visualized)
(c) biparietal diameter (when accurate measurement is possible in later stages of first trimester)
(2) Second trimester gestational age assessment includes:
(a) age is calculated by head circumference measurement/biparietal diameter and femur length using standard tables.
(3) Third trimester gestational age assessment includes:
(a) age is calculated by measurement of biparietal diameter/head circumference, femur length and abdominal circumference using standard tables.
H. Growth parameters -- For analysis of appropriate fetal growth, the following growth parameters are to be measured and compared to standard tables and, when available, earlier ultrasound examinations.
(1) Second trimester growth parameters including:
(a) biparietal diameter
(b) head circumference
(c) femur length
(2) Third trimester growth parameters measured and compared to standard tables including:
(a) estimate of fetal weight
(b) analysis of abdominal circumference (comparison with head circumference and/or standard tables may allow the detection of growth retardation).
(c) biparietal diameter
(d) head circumference
(e) femur length
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