Table 2

Derivation of the theoretical population from the observed population

	Maternal age^†	Observed population	Theoretical population (no fetal diagnosis)
Total cases	< 35	280	280
	≥ 35	132	132
	Total	412	412
Terminations	< 35	24	0
	≥ 35	50	0
	Total	74	0
Stillbirths	< 35	12	13
	≥ 35	11	18
	Total	23	31
Live births	< 35	244	266
	≥ 35	71	115
	Total	315 (76%)	383 (93%)
Liveborn cardiac abnormality total		106	129
Liveborn cardiac abnormality detectable^*		55	67

^* On routine four chamber antenatal usltrasound scan; ^† Maternal age was known for 409 cases (see text). The missing three ages were assumed to be < 35 in 2 and ≥ 35 in 1.