- Spencer K.
- Souter V.
- Tul N.
- Snijders R.
Diagnosis of Fetal Aneuploidy
First Trimester Screening
Combined ultrasound and serum markers
Screening in both First and Second Trimesters
- •All women should have the option of invasive diagnostic testing for fetal aneuploidy by CVS, if available, or amniocentesis. Benefits include diagnosis of all major aneuploidies and large chromosomal rearrangements.
- •For women who do not want any information regarding fetal aneuploidy status, following appropriate documentation, no other testing or screening is required.
- •First trimester screening (NT, PAPP-A, and hCG) is an acceptable, cost effective approach for DS risk screening for women if they present early in pregnancy (before 14 weeks' gestation).
- •Incorporation of the nasal bone assessment into the first trimester screening protocol is optional and should be limited to clinicians who have specific training and participate in an ongoing quality assurance program.
- •Women presenting in the second trimester should be offered multiple marker screening as described in the ACMG policy statement entitled Second Trimester Maternal Serum Screening for Fetal Open Neural Tube Defects and Aneuploidy (2004) (www.acmg.net).
- •Approaches that use first and second trimester screening have improved detection rates and lower false-positive rates. However, providers and centers must be prepared to ensure that there is adequate follow-up and nondisclosure is acceptable to the patient if they choose to offer integrated screening. Sequential or contingency screening with disclosure of the first trimester results may be preferable for some providers and patients.
- •Women should be informed of the adjusted risk for DS and allowed to make decisions based on this number, because individuals will weigh risk/benefits differently and are capable of such decision-making. Because age is no longer used as a cutoff to offer invasive testing, it is no longer logical to use predetermined cutoffs based on age risk for screening programs.
- •First trimester screening can be used in multifetal pregnancies; however, women should be made aware of the limitations of screening in this setting.
- •An NT measurement of 3.5 mm or greater, even in the setting of a low risk for aneuploidy screen result or normal fetal karyotype should prompt a detailed anatomic ultrasound, echocardiogram, or both.
- •Women who have elected to have first trimester screening and/or CVS should be offered MSAFP screening and/or an anatomic survey, optimally between 16 and 20 weeks' gestation for the detection of neural tube defects.
- •First trimester screening requires adherence to strict standards and maintenance of quality, both in the laboratory and ultrasound units. Sonographers must be appropriately trained in the proper technique of NT measurement and have appropriate certification through available organizations.
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