Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…in fetuses with NT ≥3.5 mm. Previous studies neither documented a diagnostic yield of 22q11 analysis after detection of first trimester increased NT (Donnenfeld et al., 2006; Lautrup et al., 2008) nor did two recent studies using MLPA analyses similar to those in the present study (Roselló et…
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