This study plans to evaluate the clinical performance of the MaterniT21 PLUS and/or GENOME Laboratory Developed Test, in the detection of fetal trisomy 21 in circulating cell-free DNA extracted from maternal blood samples obtained from women pregnant with a twin gestation.

Inclusion Criteria:

• subject pregnant with a multiple gestation and received NIPT from Sequenom Laboratories;
• subject was 18 or older at the time of NIPT

Exclusion Criteria:

• none

The Study Population will consist of women 18 years of age and older who underwent testing with a Sequenom NIPT, were pregnant with a multiple gestation at the time of testing and whose pregnancies should have outcome based upon gestational age at the time of testing.