Columbia subject headings:
Diseases in twins--Congresses.
Multiple birth--Congresses.
Twins--Congresses.
Twins--Psychology--Congresses.
Harvard subject headings:
Diseases in twins--Congresses.
Multiple birth--Congresses.
Twins--Congresses.
Twins--Psychology--Congresses.
Princeton subject headings:
Diseases in twins--Congresses.
Multiple birth--Congresses.
Twins--Congresses.
Twins--Psychology--Congresses.