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  • Trends in Birth across High-Parity: RESULTS

Temporal variations in live-born parity are shown in Table 1. Among women of moderate parity (1-4 previous live births), the birth rates declined between the first and the second period and then remained almost stable by the third period. Among high-parity women (5-9 previous live births) a linear pattern of temporal trajectory was observed, with birth rates declining consistently across the three period quar-tiles. The trend in birth rates among very-high-parity women (10-14 previous live births) was also approximately linear but in an ascending fashion. By contrast, the trend among extremely-high-parity women was nonlinear. The proportion of births among these mothers was equally high in the first and last periods (four births per 100,000) but dropped in the intervening period (down to two births per 100,000) so that the overall temporal trajectory appeared U-shaped.

Table 1. Temporal Trends in Rates of Birth by Parity Status, United States, 1989-2000

Live-Born Parity 1989-1992



P for Trend



1-4 8,628,275 (725.2)

8,212,397 (540.3)

8,345,777 (548.3)

5-9 634,152 (53.3)

615,588 (40.5)

593,626 (39.0)

10-14 8,328 (0.7)

9,120 (0.6)

18,265 (1.2)

>15 476 (0.04)

304 (0.02)

609 (0.04)


Results of trend analysis across parity subgroups by race and ethnicity are presented in Table 2. Over the study period, the total number of births among blacks and whites diminished consistently (p for trend <0.001), whereas among Hispanics the total number of deliveries increased progressively (p for trend O.001). In percentage terms, black and white women experienced an almost equal level of reduction in total deliveries, equivalent to 10% and 9.3%, respectively, over the study period. By contrast, Hispanic women again showed a substantial percentage increase in total births (almost 25%). For moderate-parity women (1^ previous live births), there appears to be no racial/ethnic variation in the rates of birth across the period quartiles. Birth rates among both moderate-parity black and white mothers were high in the initial period followed by a decline in the second period and finally a rise in the third period, thus describing an imperfect U-pattern. For moderate-parity Hispanic mothers, however, birth rates declined slightly from the first to the second period and then rose in the third period to form a J-shape pattern. Overall, a significantly net positive trend was noted for whites as well as Hispanics (0.6% and 2.0%) but not for blacks (0.07%) in this parity subgroup. order cialis super active

Table 2. Temporal Trends in Birth Rates by



1993-1996           1997-2000

P for Trend 1989-1992
Live-Born Parity


N=2,342,300         N=2,282,627

O.001 N*=2,980,763

1,383,563 (544.0)

1,253,030 (535.0)   1,242,929 (544.4)

0.6 1,617,382 (542.6)

162,512 (63.9)

158,596 (67.7)       145,684 (63.8)

0.8 192,536 (64.6)

1,832 (0.7)

2,243 (1.0)            4,450 (1.9)

O.001 2,932 (1.0)

75 (0.03)

69 (0.03)             122 (0.05)

O.001 89 (0.03)

Among high-parity black mothers (5-9 previous live births) birth rates went up moderately and then declined, whereas among Hispanics a consistent decline was noted. On the other hand, among high-parity whites, a consistent increase in birth rates was observed over the three time periods studied. Noteworthy is that the lowest birth rates in the high-parity subgroup were among white mothers. For very-high-parity mothers (10-14 previous live births), birth rates among blacks consistently increased over the years in a dose-dependent fashion (p for trend O.001). Among Hispanics, there was an initial moderate drop followed by a substantial increase, whereas for whites the rates remained stable in the first two periods followed by an increase. Again, whites tended to have consistently lower rates of birth in this parity subgroup. Among extremely-high-parity women (>15 previous live births), a positive temporal trend was noted among blacks and Hispanics only.
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Table 3. Trends in Birth Rates by Race/Ethnicity Stratified by


Maternal Age

Maternal Age

Maternal Age

Maternal Age

<30 Years

30-39 Years

>40 Years

P for Trend <30 Years
Live-Born Parity




O.001 N*=7,132,575

2,827,323 (513.0)

1,000,749 (654.0)

51,450 (576.8)

<0.001 3,591,067 (503.5)

228,325 (41.4)

216,081 (141.2)

22,386 (251.0)

O.001 193,819 (27.2)

895 (0.2)

6,156 (4.0)

1,474 (16.5)

O.001 661 (0.1)

14 (0.003)

131 (0.1)

121 (1.4)

O.001 14 (0.002)

Trends in birth rates by parity subgroups stratified by maternal race and age are presented in Table 3. Within the moderate parity category, the proportion of births was lowest among younger mothers (age <30 years) and highest among mature mothers (age 30-39 years), whereas older mothers (age >40 years) were in-between. White mothers also showed higher birth rates among older women as compared to blacks and Hispanics. Within the high-, very-high- and extremely-high-parity groups, birth rates among whites were lowest irrespective of the maternal age category and the period quartile. Also, regardless of the racial or ethnic group, birth rate was associated with increase in maternal age in a dose-effect fashion among the high-, very-high- and extremely-high-parity groups, a finding that illustrates a strong and direct correlation between advancing maternal age and increase in parity status. Because of this observation, we proceeded to esti mate the relationship between parity status and race/ ethnicity using the method of direct standardization to account for the influence of maternal age.
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Figure 1. Standardized estimates

Figure 1. Standardized estimates for the association between parity status and race/ethnicity, United States 1989-2000 (Whites are the referent group).

Figure 1 illustrates the relationship between race/ethnicity and parity status after maternal age standardization with whites as the referent group. The referent category bears an odds ratio of 1.0 (this is represented by the dashed horizontal line parallel to the X-axis). Point estimates and surrounding confidence intervals are represented by the bars. Black and Hispanic women were more likely to have higher parity as compared to whites. The racial/ethnic difference in parity status was moderate for moderate level of parity, and greatest for very-high-parity status. This difference was more manifest between black mothers and white mothers than between whites and Hispanics.

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