Focus. . . Trends in Multiple Births

Table 1 presents the rate of multiple births per 1,000 live births by race, age and birth order comparing three six-year time periods (1978-83, 1984-1989, 1990-1995). As Table 1 illustrates, the rates for the total population and for White mothers increase for all categories of age and birth order. The largest increase for white mothers was nearly 60 percent for age 35 and over with the smallest noted for ages 20-24 at 15.3 percent. After mothers 35 and older women experiencing a third birth showed the greatest increase. The change for African-American mothers is less consistent and less dramatic ranging from an increase of nearly 35 percent among mothers with third order births to decreases among fourth order births and mothers 35 and over. Rates for African-American mothers remain higher than those for white mothers with the exception of those women 35 years of age or older and women having a first birth. Some of the change in rates is due to a shift toward delayed child bearing where the rate of multiple births is higher. Consequently, the 1984-1989 distribution of births by age and birth order was used to standardize the earlier and later time periods.

As Table 1 shows, the adjusting for age decreased the change between the 1978-83 time period and the 1990-95 time period by approximately 17 percent with the exception of white mothers where there was nearly a 9 percent increase. Although the shift toward delayed child bearing is particularly evident among white mothers there has also been a corresponding increase in the proportion of multiple births occurring to teens among white females. Adjusting for birth order had little effect on the change between time periods except among African-American women. The adjusted increase between the 1978-1983 and 1990-1995 was 13 percent lower than the unadjusted for African American women. Adjusting for both birth order and age still accounts for little of the increase (less than 15 percent) of the increase in multiple births for all races and less than 10 percent of the increase among Whites. Although rates of multiple births have risen for most categories, the increase is especially noticeable among White women 35 years of age or older and women having second or third births. Most of the increase in multiple births has occurred among older mothers particularly older white mothers. Mothers 30 years of age and older account for 40 percent of multiple births compared to 31 percent of all births for 1990-95 births. In 1978-1983 the proportions were much closer among whites with older mothers giving birth to 23.7 percent of the multiple births and 22.8 percent of all births.

Multiple births are more likely to be low birth weight and thus carry a greater risk of mortality and morbidity. Figure 2 presents a comparison of singleton and multiple births for selected perinatal outcomes. Although higher order (3 or more) multiple births have even higher morbidity and mortality rates and are rapidly increasing, approximately 97 percent of multiple births are twin births. As Figure 2 illustrates, the odds of a poor outcome increase by a factor of five to eleven times for multiple births. Infant mortality in 1995 was over five times greater for multiple births than for singletons. The differentials for low birth weight and very low birth weight are even greater. Multiple births are nearly 9 times more likely than singleton births to be low birth weight and nearly 11 times more likely to be very low birth weight.

Multifetal pregnancies continue to be high risk and require early and continuous prenatal care with constant monitoring of mother and fetuses. Of course such care is possible only with early diagnosis.

References

Cumulative births also show decreases for the 8- and 12-month periods ending with August. For the 12 months ending with August, 72,794 Missouri babies were born compared with 74,803 one year earlier.

The Natural increase for Missouri in August was 2,174 (5,920 births minus 3,746 deaths). The rate of natural increase is down for all three periods shown below.