Reproduction - Birth Defects, Do We Know What The Trends Are?

The tracking of statistics on birth defects is one area in which the United States has not excelled. There is no national clearinghouse in which data on birth defects collected at the state level is brought together. Furthermore, many states do not, or did not until the late 1990s, collect data on birth defects. In 1996, Congress directed the Center for Disease Control to establish Centers of Excellence for Birth Defects Prevention and Research. As these centers are established and efforts are made to collect data on birth defects, we will know more about whether or not birth defects are on the rise or declining.

For now, we must use what data are available to try and assess trends. The chart presents data from a Center for Disease Control report on infant mortality resulting from birth defects. The percentage changes in infant deaths attributable to birth defects between 1980 and 1995 are charted. Birth defects are the leading cause of child mortality accounting for 20% of all infant deaths. Data are presented by category of birth defects¹¹. By way of reference, the incidence rate per live birth is listed under each of the largest categories. Cardiovascular defects are the most common (occurring in one infant out of every 115 newborns) and the most deadly (accounting for 31.4% of all birth defect related infant deaths in 1992, according to the American Heart Association).

One of the known risk factors associated with many birth defects is low birth weight. Therefore, included in the chart are percentage changes in the number of babies born with low birth weights and with very low birth weights. These babies have a higher risk of birth defects than babies born weighing at least 5.5 pounds. The observable trend towards greater numbers of low birth weight babies portends poorly on birth defect trends.

Six of the eight defect categories charted showed declining mortality rates over the fifteen-year period presented, from -21% for genitourinary defects to -72% for digestive system defects. This is good news, whether or not the reason for the declining mortality rates is (1) fewer children being born with life threatening abnormalities or, (2) better and more successful treatments.

Two categories that saw increased mortality were respiratory defects and chromosomal defects. Two trends that we saw earlier in this chapter may account at least in part for these increases; a higher number of premature births and a larger number of babies being born to older women. The greater the maternal age at the birth of the child, the greater the risk for chromosomal birth defects.

What we will have to await are the data that will make clear whether these changes in the numbers of infant deaths associated with birth defects are the result of fewer babies being born with abnormalities or better treatment available to care for babies who are born with birth defects. We can hope that both are true.

One thing we know to be true is that infants survive at a far greater rate now than ever before in history. The next and final panel of this chapter will address infant mortality rates and their dramatic decline in the second half of the 20th century.

Source: U.S. Center for Disease Control, Morbidity and Mortality Weekly Report, "Trends in Infant Mortality Attributable to Birth Defects — United States, 1980—1995," September 25, 1998 /47(37); pp. 773-778, available online at http://www/cdc/gov/epo/mmwr/preview/mmwrhtml/00054921.htm. Data on the incidence rates of different birth defects are from the March of Dimes, "Leading Categories of Birth Defects," a report available online at http://www.modimes.org/344_1471.htm.