. Author manuscript; available in PMC: 2010 Apr 12.

Published in final edited form as: Am J Med Genet A. 2008 Dec 15;146A(24):3147–3156. doi: 10.1002/ajmg.a.32585

Table III.

Number and percentage of relatives with MZ, DZ or DZ opposite-sex twin offspring in index mothers with spontaneous DZ and MZ twin offspring

	Index mothers with DZ twin offspring ( n= 8,222)						Index mothers with MZ twin offspring (n=5,505)

	Relative with MZ offspring		Relative with DZ offspring		Relative with DOS offspring		Relative with MZ offspring		Relative with DZ offspring		Relative with DOS offspring
	n	%	n	%	n	%	n	%	n	%	n	%
Sister	57	15.9	301	84.1^**	157	73.4^**	51	27.0	138	73.0	54	51.4
Brother	63	31.2	139	68.8^*	72	53.7	31	21.5	113	78.5	44	58.7
Mother	87	17.1	421	82.9^**	201	69.8^**	90	32.3	189	67.7	104	53.6
Aunt (M)	99	17.5	468	82.5^**	250	71.6^**	73	25.5	213	74.5	107	59.4
Uncle (M)	90	25.7	260	74.3	155	63.3	66	24.8	200	75.2	109	62.5
Grandmother (M)	90	15.3	497	84.7^**	271	75.1^**	96	29.1	234	70.9	134	58.3
Aunt (P)	87	18.0	396	82.0^**	212	70.9^**	91	32.9	186	67.1	98	51.9
Uncle (P)	75	24.8	227	75.2	112	59.9	79	31.1	175	68.9	105	57.1
Grandmother (P)	88	15.0	499	85.0^*	267	75.2^**	79	25.1	236	74.9	135	63.1
At least 1 female relative with twins	415	18.1	1,873	81.9^**	1,110	72.8^**	367	28.7	912	71.3	543	59.3

Note: M= maternal; P = paternal; DZ offspring includes opposite sex twins (DOS) offspring.

Percentages in the 2^nd and 4^th columns (relative with MZ offspring/relative with DZ offspring) sum to 100% across rows.

Percentages in column 6 (relatives with DOS offspring) are calculated as percentages of relatives with MZ + DOS offspring.

p<.05,

^**

p<.01;

significance levels are given for the comparison of the proportion of relatives with DZ versus MZ offspring in index mothers with spontaneous DZ and MZ twin offspring.