High incidence of Down's syndrome in infants of diabetic mothers.

The incidence of Down's syndrome was studied in 1870 infants of diabetic mothers out of 22,300 neonates born between January 1987 and April 1994 in our institution. All pregnancies were screened for diabetes and all cases of Down's syndrome were confirmed by chromosome analysis. Down's syndrome (all trisomy 21) was diagnosed in 35 infants: seven were born to mothers with gestational diabetes and 28 to non-diabetic mothers. The incidence of Down's syndrome was higher in infants of diabetic mothers (3.75 per 1000 v 1.36 per 1000) (p = 0.02) with a relative risk of 2.75. No significant difference was found in maternal age between both groups (p = 0.67) and the rate of Down's syndrome was higher in infants of diabetic mothers when compared with infants of non-diabetic mothers of similar age. Down's syndrome should be added to the congenital malformations already known to occur more frequently in infants of diabetic mothers.