TABLE 2.

Paired comparisons of levels of fetal red blood cell contamination between methods

Paired method	Mean estimate (%)	Lower CL (%)a	Upper CL (%)a	P value
Prick and perfusion	−0.63	−1.70	0.43	0.27
Prick and incision	−2.60	−3.55	−1.65	<0.0001
Prick and biopsy	−2.25	−3.20	−1.30	<0.0001
Prick and tissue grinding	−1.64	−2.45	−0.83	<0.0001
Perfusion and incision	−1.96	−2.97	−0.96	<0.0001
Perfusion and biopsy	−1.61	−2.55	−0.67	<0.0001
Perfusion and tissue grinding	−1.01	−1.75	−0.27	0.0002
Incision and biopsy	0.35	−0.25	0.95	0.3
Incision and tissue grinding	0.96	0.43	1.48	<0.0001
Biopsy and grinding	0.61	0.18	1.04	<0.0001

^a99% confidence limit.