Stepwise, Part 1

This statement means the Down syndrome and trisomy 18 risks did not exceed the Part 1 cutoffs. To complete the test and obtain a final result, please submit a second trimester sample within the date range provided on the Part 1 report.

A High risk for Down syndrome result indicates increased risk for the fetus to be affected with Down syndrome.

Patients with a high risk screening test result should be offered genetic counseling and the option of diagnostic testing (eg, chorionic villus sampling, amniocentesis). Cell-free DNA screening may also be offered as follow-up, but patients should be informed of its limitations.¹

The risk assessment is based in part on demographic data provided by the ordering provider. To change any demographic information used for a specific patient’s screening test, please contact Genomic Client Services at 866-GENE-INFO (1.866.436.3463).

A high risk for trisomy 18 result indicates increased risk for the fetus to be affected with trisomy 18.

Patients with a high risk screening test result should be offered genetic counseling and the option of diagnostic testing (eg, chorionic villus sampling, amniocentesis). Cell-free DNA screening may also be offered as follow-up, but patients should be informed of its limitations.¹

The risk assessment is based in part on demographic data provided by the ordering provider. To change any demographic information used for a specific patient’s screening test, please contact Genomic Client Services at 866-GENE-INFO (1.866.436.3463).

The gestational age is calculated from the crown-rump length (CRL) provided, using criteria from the Fetal Medicine Foundation. If the CRL is not provided, the gestational age is derived from the estimated date of delivery (EDD) and the collection date provided and is an exact calculation by calendar days. Gestational wheels may be inaccurate by several days or more.

Note that the gestational age is reported in decimal weeks. For example, 11 weeks 4 days is reported as 11.6 weeks.

If a first-trimester ultrasound EDD is available and the gestational age used for screening is within the EDD ±7 days, the gestational age should not be changed for screening purposes. If the gestational age used for screening is outside the ultrasound EDD range, it may be appropriate to change the gestational age used for screening.

To change the EDD/gestational age used for a specific patient’s screening test, please contact Genomic Client Services at 866-GENE-INFO (1.866.436.3463). 

If the patient has had a previous pregnancy with Down syndrome, this should be noted on the test requisition. This history may enable a more specific risk assessment. 

Prenatal screening in twin pregnancies is complex. The serum markers can be measured in a patient with a twin gestation and then divided by corresponding medians for unaffected singleton pregnancies to calculate multiple of medians (MoMs). These MoMs are then adjusted for twins in order to provide a pseudo-risk for Down syndrome.

This calculation accounts for the presence of 2 fetuses and also accounts for the chorionicity of the pregnancy and the nuchal translucency measurement of each specific fetus. The result is a pregnancy-specific pseudo-risk, rather than a fetus-specific risk.

Prenatal screening in twin pregnancies is complex. A trisomy 18 risk assessment is not calculated for twin gestations due to insufficient screening marker data from affected twin pregnancies.