MATERNAL AGE

All pregnant women have a risk of birth defects, including Down syndrome and other chromosome abnormalities. Most women don't know what their risk is, however, and may be surprised to learn what it is. The overall risk for all maternal ages in the U.S. is approximately 1 in 500 pregnancies at the time of a 2nd trimester ultrasound, based on the maternal age distribution. This risk has increased from 1 in 700 two decades ago, reflecting the trend toward delayed child birth.. Of course, the individual risk varies with the individual patient's age. The risk also decreases with gestational age because there is a certain 'attrition rate' due to the increased risk of spontaneous intrauterine death among fetuses with major chromosome abnormalities.

The table below summarizes the risk of fetal Down syndrome based on both maternal age and gestational age. The risk is reported as 1 in __. For example, a 30 year old woman has an approximate risk of 1:703 at 16 weeks.

		Gestational Age (Weeks)
		10	12	14	16	20	40
	20	983	1068	1140	1200	1295	1527
	25	870	946	1009	1062	1147	1352
	30	576	626	668	703	759	895
	31	500	543	580	610	658	776
	32	424	461	492	518	559	659
	33	352	383	409	430	464	547
	34	287	312	333	350	378	446
	35	229	249	266	280	302	356
	36	180	296	209	220	238	280
	37	140	152	163	171	185	218
	38	108	117	125	131	142	167
	39	82	89	95	100	108	128
	40	62	68	72	76	82	97
	41	47	51	54	57	62	73
	42	35	38	41	43	46	55
	43	26	29	30	32	35	41
	44	20	21	23	24	26	30
	45	15	16	17	16	19	23