TABLE 1.

Biological influences on fetal fraction

	Effect on fetal fraction	References
Feto-placental factors
Gestational age (GA)	Increases with GA	27
Crown rump length (CRL)	Increases with CRL	18
Mosaicism	Decreases	44
Fetal aneuploidy	Variable	18, 27, 31, 41
Triploidy	Decreases	43
Multiple pregnancy	Total FF increases, but FF decreases per fetus	47, 48
Maternal factors
Maternal weight	Decreases with increasing maternal weight	18, 19, 27
Maternal autoimmune disease	Decreases with active maternal disease	33, 35, 36
Low molecular weight heparin	Possible decrease	37–40
Serum PaPP-A	ncreases	18, 73
Serum free beta-HCG	ncreases	18, 74
Ethnicity	Variable	18, 48, 75
Assisted reproductive technology conception	Decreases	74
Parity	Decreases	48, 75
Maternal age	Decreases	48, 75