TABLE 2.

Comparison of twins and singletons according to oral cleft phenotype, sex and zygosity; Denmark 1968-2004.

Cohort	Phenotype/Source	Total No.	% Male	Twins vs. Singletons Prevalence Ratio (95% CI)a
All Oral Cleft Twins
	Total Oral Cleft	136	64	1.15 (0.95-1.38)
	Cleft lip	40	73	1.09 (0.77-1.53)
	Cleft lip and palate	63	76	1.43 (1.09-1.9)
	Cleft palate	33	30	0.87 (0.61-1.26)
Monozygotic Twins
	Total Oral Cleft	22	59	1.29 (0.77-2.17)
	Cleft lip	9	56	1.71 (0.83-3.52)
	Cleft lip and palate	9	78	1.42 (0.65-3.12)
	Cleft palate	4	25	0.74 (0.22-2.45)
Dizygotic Twins
	Total Oral Cleft	76	61	1.14 (0.90-1.45)
	Cleft lip	17	65	0.82 (0.50-1.37)
	Cleft lip and palate	39	77	1.57 (1.13-2.20)
	Cleft palate	20	25	0.94 (0.59-1.49)

^aControlled for cluster