Abstract
Objective
Options
Outcomes
Evidence
Values
Benefits, harms, and costs
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)Purchase one-time access:
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Footnotes
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.
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- No 262-Dépistage et diagnostic prénatals de l’aneuploïdie en ce qui concerne les grossesses gémellairesJournal of Obstetrics and Gynaecology Canada Vol. 39Issue 9