Congenital Malformations, Australia 1995-1996

Highlights

• Among 3.88 million births in the period from 1981 to 1996, 62,194 (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 4,561 (1.8%) infants born in 1995 and 4,458 (1.7%) born in 1996.
• Perinatal deaths due to congenital malformations declined from 35.9 per 10,000 births in 1973 to 15.6 per 10,000 births in 1996, 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 slightly in the same period. Congenital malformations accounted for 18.3% of perinatal deaths in 1996.
• Infant deaths due to congenital malformations declined from 28.8 per 10,000 live births in 1980 to 14.8 per 10,000 live births in 1996. Congenital malformations were the cause of 27% of infant deaths, and 10% of childhood deaths, in 1995, and 26% of infant and 10% of childhood deaths in 1996.
• In the period from 1993 to 1996, the total malformation rate of 293.5 per 10,000 among births to mothers aged 40 years and over was almost double that of 155.4 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 13 times more likely than women aged 20-24 years to give birth to an infant with a chromosomal abnormality and more than 40 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.
• The national rate of anencephalus has been declining during recent decades, with slight fluctuations in recent years. Similarly, spina bifida declined to its lowest rate of 3.0 per 10,000 births in 1994 and 1996, with a higher rate of 3.5 per 10,000 births in 1995. In 1995, there were 78 reported terminations of pregnancy for anencephalus and 55 for spina bifida, and in 1996, there were 70 and 66, respectively.
• 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.
• Following an increase in the early 1990s and then a slight decline to 1.5 per 10,000 births in 1994, the rate of gastroschisis reached its highest level of 2.1 per 10,000 births in 1996. This malformation is much more common among births to younger than to older mothers.
• Notified terminations of pregnancy for fetal malformations increased from 537 in 1992 to 722 in 1994, then fell to 527 in 1996, but notification was incomplete. The main indications for termination of pregnancy were trisomy 21 (Down syndrome), other chromosomal abnormalities, neural tube defects (anencephalus and spina bifida) and cardiac defects. Most terminations of pregnancy for fetal malformations (78.6%) were performed at gestational ages between 16 and 22 weeks.
• Reported terminations of pregnancy for trisomy 21 (Down syndrome) and for trisomy 18 (Edwards syndrome) were higher in 1994 than in any previous year, but then declined to 113 and 45, respectively, in 1996.