Table B1.

Parameters for overlapping distributions in Down's syndrome and unaffected pregnancies according to method

	Mixture model method (NT, mm)				Standard MoM method (NT MoM)
	Down's syndrome		Unaffected		Down's syndrome	Unaffected
Parameter	CRL dependent	CRL independent	CRL dependent	CRL independent
Median
11 completed weeks	1.29		1.29		2.50
12 completed weeks	1.70		1.70		1.92
13 completed weeks	1.96		1.96		1.67
Standard deviation (log10)
11 completed weeks					0.2289	0.1165
12 completed weeks					0.2180	0.0969
13 completed weeks					0.2136	0.0911
Proportion
11 completed weeks			0.8993	0.1007	–	–
12 completed weeks			0.9359	0.0641	–	–
13 completed weeks			0.9613	0.0387	–	–

NT, nuchal translucency; CRL, crown–rump length; MoM, multiple of the median