• Fleischer AC, Andreotti RF, Bohm-Velez M, Horrow MM, Hricak H, Javitt MC, Thurmond A, Zelop C, Expert Panel on Women's Imaging. Multiple gestations. [online publication]. Reston (VA): American College of Radiology (ACR); 2005. 10 p. [22 references]

This is the current release of the guideline.

This guideline updates a previous version: American College of Radiology (ACR), Expert Panel on Women's Imaging. Evaluation of multiple gestations. Reston (VA): American College of Radiology (ACR); 2001. 11 p. (ACR appropriateness criteria).

The appropriateness criteria are reviewed annually and updated by the panels as needed, depending on introduction of new and highly significant scientific evidence.

Multiple gestations

Note: For simplicity and clarity, the appropriateness criteria have been applied to twin pregnancies initially diagnosed in the second trimester. They are applicable to twins first identified in the third trimester with little if any alteration of the schema. For twins identified in the first trimester, a scan for detailed anatomic evaluation and comparative growth is recommended at 18-20 weeks, with other aspects of these guidelines applicable thereafter. Triplet and higher order multiple gestations are not specifically addressed, but these should all be treated as very high-risk pregnancies.

Diagnosis
Evaluation

Obstetrics and Gynecology
Radiology

Health Plans
Hospitals
Managed Care Organizations
Physicians
Utilization Management

To evaluate the appropriateness of radiologic examinations for women with multiple gestations

Women with multiple gestations (specifically, women with twin pregnancies initially diagnosed in the second trimester)

Diagnosis/Evaluation

1. Ultrasound diagnosis of multiple gestation
   • Characterization of type of twinning
   • Determination of chorionicity and amnionicity
   • Assessment of size of each twin and degree of discordance
2. Timing of follow-up ultrasound examinations
3. Additional evaluations
   • Assessment of amniotic fluid for each twin
   • Assessment of cervix
   • Umbilical artery Doppler for each twin
   • Biophysical profile for each twin
   • Nonstress test for each twin

Diagnostic utility (i.e., sensitivity, specificity) of ultrasound techniques

Searches of Electronic Databases

The guideline developer performed literature searches of peer-reviewed medical journals, and the major applicable articles were identified and collected.

The total number of source documents identified as the result of the literature search is not known.

Weighting According to a Rating Scheme (Scheme Not Given)

Not stated

Systematic Review with Evidence Tables

One or two topic leaders within a panel assume the responsibility of developing an evidence table for each clinical condition, based on analysis of the current literature. These tables serve as a basis for developing a narrative specific to each clinical condition.

Expert Consensus (Delphi)

Since data available from existing scientific studies are usually insufficient for meta-analysis, broad-based consensus techniques are needed to reach agreement in the formulation of the appropriateness criteria. The American College of Radiology (ACR) Appropriateness Criteria panels use a modified Delphi technique to arrive at consensus. Serial surveys are conducted by distributing questionnaires to consolidate expert opinions within each panel. These questionnaires are distributed to the participants along with the evidence table and narrative as developed by the topic leader(s). Questionnaires are completed by the participants in their own professional setting without influence of the other members. Voting is conducted using a scoring system from 1 to 9, indicating the most to the least appropriate imaging examination or therapeutic procedure. The survey results are collected, tabulated in anonymous fashion, and redistributed after each round. A maximum of three rounds is conducted and opinions are unified to the highest degree possible. Eighty percent agreement is considered a consensus. This modified Delphi technique enables individual, unbiased expression, is economical, easy to understand, and relatively simple to conduct.

If consensus cannot be reached by the Delphi technique, the panel is convened and group consensus techniques are utilized. The strengths and weaknesses of each test or procedure are discussed and consensus reached whenever possible. If "No consensus" appears in the rating column, reasons for this decision are added to the comment sections.

Not applicable

A formal cost analysis was not performed and published cost analyses were not reviewed.

Internal Peer Review

Criteria developed by the Expert Panels are reviewed by the American College of Radiology (ACR) Committee on Appropriateness Criteria.

ACR Appropriateness Criteria®

Clinical Condition: Multiple Gestations

Variant 1: Indications for use of ultrasound to diagnose multiple gestations.

Variant 2: Initial ultrasound has diagnosed twins on the same scan.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Clinical Condition: Multiple Gestations: Follow-up Scans

Variant 3: First ultrasound: dichorionic twins, concordant.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 4: First ultrasound: monochorionic twins, concordant.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 5: First ultrasound: monoamniotic twins, concordant.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 6: First or subsequent ultrasound: 5% twin discordance.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 7: First or subsequent ultrasound: 10% twin discordance.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 8: First or subsequent ultrasound: 15% twin discordance.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 9: First or subsequent ultrasound: 20% twin discordance.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 10: First or subsequent ultrasound: 25% twin discordance.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 11: First or subsequent ultrasound: oligohydramnios in one or both sacs.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 12: First or subsequent ultrasound: anomaly in a twin.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 13: Parameters to measure for twin discordance.

Variant 14: Tables to use for twin measurement.

All multiple gestations are high-risk as compared with singleton pregnancies. Dichorionic twin pregnancies, all of which must also be diamniotic, are the safest form of twinning and carry a 10% risk that one or both fetuses will not survive beyond the neonatal period. When twins share one placenta--monochorionic-diamniotic twinning--that risk increases to 25%, with the increased mortality due to complications related to blood vessel communications between the cardiovascular circulations of the individual twins. These conditions include twin-twin transfusion syndrome (TTTS), twin embolization syndrome, and acardius, or twin-reversed arterial perfusion sequence. When twins also share the same compartment--monochorionic-monoamniotic twinning--the loss rate jumps to 50%, with the incremental mortality attributable to cord entanglement accidents.

The major sources of morbidity and mortality common to all twin gestations are prematurity and intrauterine growth restriction, which may affect one or both fetuses. There may be an earlier onset to placental postmaturity complications. There is also an increased incidence of congenital anomalies among all twins, although anatomic malformations occur 4 to 5 times as frequently in monozygotic as in dizygotic twins. All categories of perinatal morbidity and mortality among twins occur with even greater frequency in higher order multiple gestations.

It has been the task of the guideline committee to determine, by evaluation of the medical literature and use of consensus techniques, the appropriate modalities (sonographic and others) and the timing and frequency of their use for assessing the health status of multiple gestations. For simplicity and clarity, the appropriateness criteria have been applied to twin pregnancies initially diagnosed in the second trimester. They are applicable to twins first identified in the third trimester with little if any alteration of the schema. For twins identified in the first trimester, a scan for detailed anatomic evaluation and comparative growth is recommended at 18 to 20 weeks, with other aspects of these guidelines applicable thereafter.

Triplet and higher order multiple gestations are not specifically addressed, but these should all be treated as very high-risk pregnancies. Growth scans should be performed no less frequently than every 3 to 4 weeks. Some form of fetal monitoring, probably best accomplished by some variant of the sonographic biophysical profile (since it is very difficult to confirm that nonstress tests have successfully interrogated each fetus of a triplet or greater multifetal pregnancy), should be considered on a weekly or more frequent basis once the pregnancy has reached the point of potential postnatal viability. Even closer surveillance may be indicated if there is a monochorionic or monoamniotic twin pair as part of the multifetal pregnancy, particularly if there is discordance in fetal sizes or amniotic fluid volumes.

Firm indications for use of sonography to diagnose multiple gestations include those pregnancies that measure larger than anticipated by menstrual dates and all pregnancies conceived with assisted reproductive techniques. A less strong, but possible, indication is pregnancy when there is a family history of spontaneous twins. Some would argue that the timely diagnosis of multiple gestations and the consequent alteration of obstetrical management could be used to consider sonographic second trimester screening of all pregnancies, but no statistically significant fetal benefits were demonstrated in the recent RADIUS trial. Elevation of maternal serum alpha-fetoprotein is an indication for sonography, and one of the causes for a high value is multiple pregnancy.

Once a twin pregnancy is diagnosed, sonography is an important method by which to characterize the type of twinning that has occurred and to identify prognostic indicators of possible adverse outcome. During the scan that has diagnosed twins, it is necessary to attempt to determine chorionicity and amnionicity; assess the size of each twin and the degree of discordance, if any, between them; evaluate the amount of amniotic fluid for each; and image the cervix to check for changes of effacement or dilatation. On each indicated follow-up sonogram, it remains equally important to measure twins for development of discordance, and to evaluate the cervix and each twin's amniotic fluid. Unless there is evidence of significant growth restriction or fluid volume abnormality for one or both twins, it is probably not indicated to perform umbilical artery Doppler waveform analysis (UAD) or biophysical profile (BPP) on the twins. While Doppler interrogation is not indicated, even in concordant twins, nonstress test (NST) is warranted starting at 32 weeks. It is similarly important and possible to determine chorionicity and amnionicity in triplet pregnancies.

The timing and frequency of follow-up sonograms should be adjusted based on the chorionicity and amnionicity of the twin pregnancy, attempting to minimize the number of scans performed, unless growth or fluid disturbances indicate a need for closer surveillance. There was no consensus on the ideal study intervals, but there were definite opinion trends for concordant twins without detected sonographic complicating factors. For dichorionic-diamniotic twins, a single follow-up scan in the first portion of the third trimester, 26 to 32 weeks, is most probably sufficient, although some preferred periodic scans at 6-week intervals. For monochorionic-diamniotic twins, there was a definite preference for sequential scans at timed intervals between 3 and 6 weeks, with 3- to 4-week intervals most commonly selected because of the increased risk of TTTS in 15% if these cases. The scanning pattern recommendation for monochorionic-monoamniotic twins was similar, between 3 and 6 weeks, but with 3 to 4 week intervals preferred.

The necessary parameters to measure or calculate in assessing the likelihood of intrauterine growth restriction include weight and abdominal circumference. Measurements of biparietal diameter, head circumference, and femur length are all indicated, but ratios of head or femur to abdominal circumference are probably not needed. The use of the same measurement tables developed for singleton pregnancies is indicated for twins rather than tables specifically generated for twins. Twin pregnancies are at greater risk of intrauterine growth restriction, which may affect one or both fetuses, and there is concern that growth tables for twins, which do show smaller measurements than singletons in the third trimester, may be incorporating tendencies toward growth restriction within their normal values. It is important to remember that twins can be concordantly growth-restricted, and if both are becoming small for dates on follow-up sonograms, protocols for monitoring fetal well-being will still be indicated, just as they would be in significantly discordant twins.

Twin discordance is considered mild if weight estimates for the twins are 15% different, moderate if 20% different, and severe if 25% different or greater. For mild discordance, scans for growth at 3-week intervals with use of umbilical artery Doppler analysis are probably indicated. For moderate discordance, scans for growth at 2 to 3 week intervals should be considered, and UAD, BPP, and/or NST are indicated. When discordance is severe, growth scans at 2-week intervals are preferred, with BPP and/or NST necessary and UAD also indicated. If both twins have fallen below the 10th percentile for gestational age relative to menstrual dates and/or dating by the initial sonogram, that should also be taken as an indication for increased surveillance of growth and fetal health.

Approximately 10 to 20% of monochorionic twin pregnancies may be associated with TTTS, a type of twin discordance. In addition to the evaluation of amniotic fluid volume, bladder volume, and hydrops in each twin, Doppler findings may be used to assess these pregnancies complicated by intertwin vascular connections within the placenta, between cord insertion sites, for the presence of an A-A anastomosis. Other Doppler findings include absent or reversed end-diastolic flow within the umbilical artery, pulsatile umbilical vein flow, and absent or reversed end-diastolic flow within the ductus venosus.

Testing for fetal well-being by BPP and NST are generally performed weekly, twice weekly, or even more frequently when there is strong clinical concern for imminent fetal decompensation. Umbilical artery Doppler is, in general, not a rapidly fluctuating or deteriorating parameter, but rather a long-term predictor of the status of the utero-placental circulation. As such, it has prognostic significance for the likelihood of growth restriction and perinatal morbidity and mortality, and it may change weekly if abnormal.

Oligohydramnios in one or both amniotic sacs is an important risk factor for poor perinatal outcome. In monochorionic twins, oligohydramnios for one fetus may indicate severe growth restriction if amniotic fluid for the other is normal, or it may indicate the possibility of the twin-twin transfusion syndrome if the other twin has polyhydramnios. With oligohydramnios, growth scans are needed every 2 weeks, and frequent well-being assessment by BPP and/or NST is also necessary. UAD, at appropriate intervals, is also indicated.

Closer surveillance of twin pregnancies in which one or both twins have anatomic anomalies is also indicated, generally at 3- to 4-week intervals. The intervals and the potential use of UAD, BPP, and/or NST should be based on the specific abnormality present and the likelihood that it would affect fetal well-being or amniotic fluid volume.

The evaluation of multiple gestations is a challenging and important task. The intensity of the obstetrical management of such pregnancies must be titrated to the degree of risk present in each individual case. The number of fetuses present, their chorionic and amniotic status, and risk factors such as growth restriction of one or more fetuses, amniotic fluid alterations, or presence of fetal anomalies must all be taken into account. These parameters will all affect the frequency of growth assessment, the intensity of surveillance for fetal well-being, and the institution of pharmacological and other medical therapeutic interventions. Ultrasonographic imaging, together with its associated techniques for monitoring fetal compensation or distress, serves as the mainstay for evaluating the complexities of each multifetal pregnancy, helping the obstetrician chart a course toward a successful outcome.

Abbreviation

US, ultrasound

Algorithms were not developed from criteria guidelines.

The recommendations are based on analysis of the current literature and expert panel consensus.

Selection of appropriate radiologic imaging procedures for evaluation of women with multiple gestations

Not stated

An American College of Radiology (ACR) Committee on Appropriateness Criteria and its expert panels have developed criteria for determining appropriate imaging examinations for diagnosis and treatment of specified medical condition(s). These criteria are intended to guide radiologists, radiation oncologists, and referring physicians in making decisions regarding radiologic imaging and treatment. Generally, the complexity and severity of a patient's clinical condition should dictate the selection of appropriate imaging procedures or treatments. Only those exams generally used for evaluation of the patient's condition are ranked. Other imaging studies necessary to evaluate other co-existent diseases or other medical consequences of this condition are not considered in this document. The availability of equipment or personnel may influence the selection of appropriate imaging procedures or treatments. Imaging techniques classified as investigational by the U.S. Food and Drug Administration (FDA) have not been considered in developing these criteria; however, study of new equipment and applications should be encouraged. The ultimate decision regarding the appropriateness of any specific radiologic examination or treatment must be made by the referring physician and radiologist in light of all the circumstances presented in an individual examination.

An implementation strategy was not provided.

Staying Healthy

Effectiveness
Timeliness

• Fleischer AC, Andreotti RF, Bohm-Velez M, Horrow MM, Hricak H, Javitt MC, Thurmond A, Zelop C, Expert Panel on Women's Imaging. Multiple gestations. [online publication]. Reston (VA): American College of Radiology (ACR); 2005. 10 p. [22 references]

Not applicable: The guideline was not adapted from another source.

2001 (revised 2005)

American College of Radiology - Medical Specialty Society

The American College of Radiology (ACR) provided the funding and the resources for these ACR Appropriateness Criteria®.

Committee on Appropriateness Criteria, Expert Panel on Women's Imaging

Panel Members: Arthur C. Fleischer, MD (Co-Author and Panel Chair); Rochelle F. Andreotti, MD (Co-Author); Marcela Böhm-Vélez, MD; Mindy M. Horrow, MD; Hedvig Hricak, MD, PhD; Marcia C. Javitt, MD; Amy Thurmond, MD; Carolyn Zelop, MD

Not stated

This is the current release of the guideline.

This guideline updates a previous version: American College of Radiology (ACR), Expert Panel on Women's Imaging. Evaluation of multiple gestations. Reston (VA): American College of Radiology (ACR); 2001. 11 p. (ACR appropriateness criteria).

The appropriateness criteria are reviewed annually and updated by the panels as needed, depending on introduction of new and highly significant scientific evidence.

None available

This NGC summary was completed by ECRI on November 19, 2004. The information was verified by the guideline developer on December 21, 2004. This summary was updated by ECRI on March 23, 2006.