Among 3.37 million births in the period from 1981 to 1994, 53,065 (1.6%) infants with major congenital malformations diagnosed at birth or in the first 28 days were notified to the national monitoring system. These included 4,426 (1.7%) infants born in 1993 and 4,297 (1.6%) in 1994.
Perinatal deaths due to congenital malformations declined from 35.9 per 10,000 births in 1973 to 17.5 per 10,000 births in 1994, the lowest level of any year. The perinatal death rate for anencephalus showed the most pronounced decline but there were also substantial falls for spina bifida, hydrocephalus and congenital heart defects. Perinatal death rates due to chromosomal abnormalities increased in the same period. Congenital malformations accounted for 22% of perinatal deaths in 1994.
Infant deaths due to congenital malformations declined from 28.8 per 10,000 live births in 1980 to 17.6 per 10,000 live births in 1994. Congenital malformations were the cause of 30% of infant deaths, and 10% of childhood deaths,' in 1994.
In the period from 1992 to 1994, the total malformation rate of305.9 per 10,000 among births to mothers aged 40 years and over was almost double that of 154.8 per 10,000 among births to mothers aged 20-24 years. Chromosomal abnormalities were more likely with advancing maternal age. Women aged 40 years and over were 12 times more likely than women aged 20-24 years to give birth to an infant with a chromosomal abnormality and more than 60 times more likely to have a termination of pregnancy before 20 weeks' gestation.
Isolated and multiple malformations were more common in twins and other multiple births than in singleton births.
Following a marked decline in the rate of anencephalus among births up to 1992, there was a slight increase in 1993 but then a continuation of the downward trend in 1994. Spina bifida also declined to its lowest rate of2.9 per 10,000 births in 1994. In that year, there were 84 reported terminations of pregnancy for anencephalus and 70 for spina bifida, the largest numbers in any year.
Increasing rates of ventricular septal defect and obstructive defects of the renal pelvis and ureter are likely to reflect better ascertainment, particularly by prenatal ultrasound screening for the renal defects.
The rate of gastroschisis reached its highest level of 2.0 per 10,000 births in 1993 and then declined to 1.5 per 10,000 births in 1994. This malformation is much commoner among births to younger than to older mothers.
Notified terminations of pregnancy for fetal malformations increased from 421 in 1991 to 718 in 1994, but notification was incomplete. The main indications for termination of pregnancy were trisomy 21 (Down syndrome), other chromosomal abnormalities and neural tube defects (anencephalus and spina bifida). Most terminations of pregnancy for fetal malformations (75.7%) were performed at gestational ages between 16 and 22 weeks.
The number of reported terminations of pregnancy for trisomy 21 (Down syndrome) and for trisomy 18 (Edwards syndrome) was higher in 1994 than in any previous year - 128 and 48, respectively.