Abstract
Objective
To provide a Canadian consensus document with recommendations on prenatal screening
for and diagnosis of fetal aneuploidy (e.g., Down syndrome and trisomy 18) in twin
pregnancies.
Options
The process of prenatal screening and diagnosis in twin pregnancies is complex. This
document reviews the options available to pregnant women and the challenges specific
to screening and diagnosis in a twin pregnancy.
Outcomes
Clinicians will be better informed about the accuracy of different screening options
in twin pregnancies and about techniques of invasive prenatal diagnosis in twins.
Evidence
PubMed and Cochrane Database were searched for relevant English and French language
articles published between 1985 and 2010, using appropriate controlled vocabulary
and key words (aneuploidy, Down syndrome, trisomy, prenatal screening, genetic health
risk, genetic health surveillance, prenatal diagnosis, twin gestation). Results were
restricted to systematic reviews, randomized controlled trials, and relevant observational
studies. Searches were updated on a regular basis and incorporated in the guideline
to August 2010. Grey (unpublished) literature was identified through searching the
websites of health technology assessment and health technology assessment-related
agencies, clinical practice guideline collections, clinical trial registries, and
national and international medical specialty societies. The previous Society of Obstetricians
and Gynaecologists of Canada guidelines regarding prenatal screening were also reviewed
in developing this clinical practice guideline.
Values
The quality of evidence was rated using the criteria described in the Report of the
Canadian Task Force on Preventive Health Care (Table 1).
Benefits, harms, and costs
There is a need for specific guidelines for prenatal screening and diagnosis in twins.
These guidelines should assist health care providers in the approach to this aspect
of prenatal care of women with twin pregnancies.
Summary Statements
- 1.Fetal nuchal translucency combined with maternal age is an acceptable first trimester screening test for aneuploidies in twin pregnancies (II-2).
- 2.First trimester serum screening combined with nuchal translucency may be considered in twin pregnancies. It provides some improvement over the performance of screening by nuchal translucency and maternal age by decreasing the false-positive rate (II-3).
- 3.Integrated screening with nuchal translucency plus first and second trimester serum screening is an option in twin pregnancies.Further prospective studies are required in this area, since it has not been validated in prospective studies in twins (III).
- 4.Non-directive counselling is essential when invasive testing is offered (III).
- 5.When chorionic villus sampling is performed in non-monochorionic multiple pregnancies, a combination of transabdominal and transcervical approaches or a transabdominal only approach appears to provide the best results to minimize the likelihood of sampling errors (II-2).
Recommendations
- 1.All pregnant women in Canada, regardless of age, should be offered, through an informed counselling process, the option of a prenatal screening test for the most common clinically significant fetal aneuploidies. In addition, they should be offered a second trimester ultrasound for dating, assessment of fetal anatomy, and detection of multiples (I-A).
- 2.Counselling must be non-directive and must respect a woman's right to accept or decline any or all of the testing or options offered at any point in the process (III-A).
- 3.When non-invasive prenatal screening for aneuploidy is available, maternal age alone should not be an indication for invasive prenatal diagnosis in a twin pregnancy (II-2A). If non-invasive prenatal screening is not available, invasive prenatal diagnosis in twins should be offered to women aged 35 and over (II-2B).
- 4.Chorionicity has a major impact on the prenatal screening process and should be determined by ultrasound in the first trimester of all twin pregnancies (II-2A).
- 5.When screening is done by nuchal translucency and maternal age, a pregnancy-specific risk should be calculated in monochorionic twins. In dichorionic twins, a fetus-specific risk should be calculated (II-3C).
- 6.During amniocentesis, both amniotic sacs should be sampled in monochorionic twin pregnancies, unless monochorionicity is confirmed before 14 weeks and the fetuses appear concordant for growth and anatomy (II-2B).
- 7.Prior to invasive testing or in the context of twins discordant for an abnormality, selective reduction should be discussed and made available to those requesting the procedure after appropriate counselling (III-B).
- 8.Monitoring for disseminated intravascular coagulopathy is not indicated in dichorionic twin pregnancies undergoing selective reduction (II-2B).
Key Words
Abbreviations:
AFP (alpha fetoprotein), CVS (chorionic villus sampling), DR (detection rate), FPR (false-positive rate), hCG (human chorionic gonadotropin), NT (nuchal translucency), PAPP-A (pregnancy-associated plasma protein A), uE3 (unconjugated estriol)To read this article in full you will need to make a payment
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Article Info
Publication History
No. 262 (Replaces No. 187, February 2007)
Footnotes
This guideline was peer reviewed by the SOGC's Genetics Committee in January 2017 and has been reaffirmed for continued use until further notice. Please note updated content can be reviewed in the Clinical Practice Guideline: No. 348-Joint SOGC-CCMG Guideline: Update on Prenatal Screening for Fetal Aneuploidy, Fetal Anomalies, and Adverse Pregnancy Outcomes [September 2017].
This clinical practice guideline has been prepared by the Genetics Committee of the Society of Obstetricians and Gynaecologists of Canada (SOGC) and the Prenatal Diagnosis Committee of the Canadian College of Medical Geneticists (CCMG) and approved by the Executive and Council of the Society of Obstetricians and Gynaecologists of Canada and the Board of Directors of the Canadian College of Medical Geneticists.
Disclosure statements have been received from all members of the committees.
Identification
Copyright
© 2017 Published by Elsevier Inc. on behalf of The Society of Obstetricians and Gynaecologists of Canada/La Société des obstétriciens et gynécologues du Canada
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