MEDLINE (Ovid)
Steps	Text words and subject headings	Sets of search
1	'cell‐free dna'.mp	Index test
2	'cell free dna'.mp
3	cfdna.mp
4	ffdna.mp
5	cffdna.mp
6	'free foetal dna'.mp
7	'free fetal dna'.mp
8	nipd.mp
9	nipt.mp
10	(non invasive or noninvasive or non‐invasive).mp
11	(genetic adj2 (diagnos* or detect* or test* or screen*)).mp
12	exp Genetic Testing/
13	exp Sequence Analysis, DNA/
14	((antenatal or ante natal) adj2 (diagnos* or detect* or test* or screen*)).mp
15	((prenatal or pre natal) adj2 (diagnos* or detect* or test* or screen*)).mp
16	exp Prenatal Diagnosis/
17	or/1‐16
18	maternal.mp	Patient description
19	exp Pregnancy/
20	exp Pregnancy Complications/
21	pregnant.mp
22	pregnanc*.mp
23	exp Fetus/
24	fetus.mp
25	foetus.mp
26	fetal.mp
27	foetal.mp
28	or/18‐27
29	trisom*.mp	Target condition
30	aneuploid*.mp
31	(down* adj syndrome*).mp
32	exp Aneuploidy/
33	exp Trisomy/
34	exp Down Syndrome/
35	chromosome disorders.mp
36	or/29‐35
37	or/1‐5,11‐13	Combined sets
38	6 or 7 or 8 or 9 or 14 or 15 or 16
39	36 and 37 and 28 and 10
40	38 and 37 and 36
41	39 or 40	Final combined set