The purpose of this blinded, multi-center, prospective, case-controlled study is to compare the Ariosa Harmony™ Prenatal Test for trisomy 21 detection with a standard first-trimester prenatal screening test consisting of serum screening (PAPP-A,free beta-hCG [β-hCG] or total hCG) and a nuchal translucency (NT) measurement (i.e. combined first trimester screening) in a general screened population.

The performance characteristics of these two test modalities will be assessed relative to the clinical reference standard of genetic analysis of the fetus or phenotypic characterization and genetic analysis of the newborn.

Inclusion Criteria:

1. Subject is at least 18 years old and can provide informed consent.
2. Subject is planning a hospital delivery.
3. Subject has a singleton pregnancy with a documented gestational age between 10 weeks, 0 days, and 14 weeks, 2 days, inclusive, at the time of the study blood sample collection.
4. Subject is planning to undergo combined first trimester prenatal screening that includes NT measurement, and when indicated, serum screening with total or free β-hCG and PAPP-A.

Exclusion Criteria:

1. Subject has known aneuploidy.
2. Subject has active or history of malignancy requiring major surgery and/or systemic chemotherapy.
3. Subject has a twin demise at any gestational age. Twin demise includes any reductions, spontaneous or elective, after sonographic identification of a second (or more) gestational sac. Any clinical, sonographic, or other testing that suggests twin demise would serve as an exclusion criterion.

Pregnant women presenting for combined first trimester screening as part of routine prenatal care