Small-for-gestational-age births in the United States: an age-period-cohort analysis

BACKGROUND: During the last 2 decades, the rate of low birthweight has increased, as has the rate of preterm delivery, among both whites and blacks. Examination of causes for these secular trends has focused largely on changes in the distributions of maternal age and, less commonly, on birth cohort. Little is known as to how age, period, and birth cohort interact on trends in small births at term. METHODS: The U.S. natality files were used to assess trends in term (>/=37 weeks gestation) small-for-gestational age (SGA) births for 7 5-year maternal age groups (15-19 through 45-49 years), 6 delivery periods (1975, 1980, 1985, 1990, 1995, and 2000), and 12 5-year maternal birth cohorts (1926-1930 through 1981-1985). SGA births were defined as sex-specific birthweight below the 10th percentile for gestational age based on 1995 livebirths in the United States. Logistic regression models were fit to determine the independent effects of age, delivery period, and birth cohort on term SGA trends, separately for blacks and whites. RESULTS: Between 1975 and 2000, term SGA births declined by 23% (from 21% to 16%) among blacks and by 27% (from 12% to 9%) among whites. Term SGA births declined with increasing age up to 30-34 years, but increased among older women. Within strata of maternal age, the risk also declined with later maternal birth cohorts, among both blacks and whites. The strongest influence on SGA trends was from maternal age, followed by maternal birth cohort, and lastly by delivery period. In general, for any combination of age, period, and birth cohort, blacks showed 1.5- to 2-fold higher rates of term SGA than whites. CONCLUSIONS: The persistence of strong maternal age effects on risk of term SGA births suggests that the effect of age is at least partly the result of biologic factors. Term SGA trends were generally consistent for blacks and whites, although the magnitude of difference in the risks for combinations of age, period, or mother's birth cohort was higher among blacks than whites.     

Improvement in infant and perinatal mortality in the United States, 1965--1973: I. Priorities for intervention

Changes in United States infant and perinatal mortality in the period 1965--1973 were examined by race, age at death or length of gestation, and degree of urbanization. The decline of postneonatal mortality rates was greater than the declines of fetal and neonatal mortality rates. Other-than white infant and fetal mortality rates improved more than the white rates, except in the first day of life. Postneonatal mortality rates improved more in rural than in urban areas, while neonatal and perinatal mortality rates improved more in urban areas than in rural. These improvements in mortality rates have occurred at the same time as changes in medical techniques and the organization and availability of health services, improvements in economic conditions and standards of living, and changes in the demographic characteristics of the child-bearing population of the United States. Each of these changes was in a direction expected to have a favorable effect on infant and perinatal mortality. Nevertheless, the improvement of infant mortality rates has not changed the relative position of the United States in comparison with other countries. Programs to improve infant and perinatal mortality can use the data in this study to define high priority target groups using a method based on the size of the problem in the target group, the severity of the problem, and the amount and direction of change.     

Neighbourhood deprivation and small-for-gestational-age term births in the United States

Residential context has received increased attention as a possible contributing factor to race/ethnic and socio-economic disparities in birth outcomes in the United States. Utilising vital statistics birth record data, this study examined the association between neighbourhood deprivation and the risk of a term small-for-gestational-age (SGA) birth among non-Hispanic whites and non-Hispanic blacks in eight geographical areas. An SGA birth was defined as a newborn weighing <10th percentile of the sex- and parity-specific birthweight distribution for a given gestational week. Multi-level random intercept logistic regression models were employed and statistical tests were performed to examine whether the association between neighbourhood deprivation and SGA varied by race/ethnicity and study site.
The risk of term SGA was higher among non-Hispanic blacks (range 10.8–17.5%) than non-Hispanic whites (range 5.1–9.2%) in all areas and it was higher in cities than in suburban locations. In all areas, non-Hispanic blacks lived in more deprived neighbourhoods than non-Hispanic whites. However, the adjusted associations between neighbourhood deprivation and term SGA did not vary significantly by race/ethnicity or study site. The summary fully adjusted pooled odds ratios, indicating the effect of one standard deviation increase in the deprivation score, were 1.15 [95% CI 1.08, 1.22] for non-Hispanic whites and 1.09 [95% CI 1.05, 1.14] for non-Hispanic blacks. Thus, neighbourhood deprivation was weakly associated with term SGA among both non-Hispanic whites and non-Hispanic blacks.     

Repeat Unintended, Unwanted and Seriously Mistimed Childbearing in the United States

CONTEXT: The high level of unintended fertility in the United States is a serious public health issue. Whether unintended fertility occurs across the population or is concentrated among a subset of women who experience multiple unintended births is unclear.
METHODS: Data from the 2002 National Survey of Family Growth were used to determine levels of unintended, unwanted and seriously mistimed childbearing, and chi-square and t tests were used to identify group differences in these measures, in two cohorts of women (those born in 1958–1962 and those born in 1965–1969). Both births (by ages 33–37) and mothers were used as units of analysis.
RESULTS: The proportion of births identified as unintended was greater in the 1965–1969 cohort than in the earlier cohort (37% vs. 34%), largely because a higher proportion of births to women in the former cohort were unwanted. In both cohorts, more than a third of women (36–41%) reporting at least one unintended birth had had at least one more, and women reporting unintended or unwanted births had higher overall fertility than others. Levels of repeat unintended fertility were greatest among black women, and the proportion of blacks who reported two or more unwanted births was 94% higher in the 1965–1969 cohort than in the 1958–1962 cohort (19% vs. 10%).
CONCLUSIONS: Repeat unintended fertility is common, especially among black women, who may differ from other groups in their contraceptive and fertility decisions as well as in their access to and ability to afford family planning services.     

Excess salmonellosis in women in the United States: 1968-2000

We describe recent epidemiological changes in salmonellosis. Linking 1968-2000 National Salmonella Surveillance System to census data, we calculated population-based age- and sex-stratified rates of non-urinary salmonellosis for the top 30 non-typhoidal serotypes. Using 1996-1997, 1998-1999, and 2000-2001 population-based FoodNet surveys, we compared reported diarrhoea, medical visits, and stool cultures. Despite an overall female-to-male incidence rate ratio (FMRR) of 0.99, the sex-specific burden of salmonellosis varied by age (<5 years FMRR 0.92; 5-19 years 0.85; 20-39 years 1.09; 40-59 years 1.23, and 60 years 1.08) and serotype (FMRR range 0.87 for Mississippi to 1.25 for Senftenberg). Serotype-specific FMRRs and median age (range 2 years for Derby to 29 years for Senftenberg) were related (correlation 0.76, P<0.0001). Recently, the relative burden of salmonellosis in women has increased. FoodNet data suggest that this change is real rather than due to differential reporting. Excess salmonellosis in women may reflect differences in exposure or biological susceptibility.     

Seroprevalence of zoonotic toxocariasis in the United States: 1971-1973

Demographic characteristics associated with human Toxocara canis infection in children aged one to 11 years were investigated using data from the Health and Nutrition Examination Survey of 1971 to 1973. An enzyme-linked immunosorbent assay with larval stage antigen was used to measure the concentration of antibodies to T. canis in 1,409 available sera. From 4.6 to 7.3% of the children in different geographic regions of the United States have been infected, with serologic prevalence approaching 30% among black children of lower socioeconomic status aged six to 11 years. For both blacks and whites, higher seroprevalence was associated with a rural residence, increased age in children and number of persons in the household, and with decreased income, education, and number of rooms in the house. Multivariate logistic regression models indicated that blacks had higher infection rates than whites, even when socioeconomic factors were controlled. Certain critical variables, however, such as exposure to dogs or reliable pica histories, were not available for analysis.     

Placental abruption among singleton and twin births in the United States: risk factor profiles

The authors performed a population-based epidemiologic study to evaluate and contrast risk factor profiles for placental abruption among singleton and twin gestations. Data were derived from linked US birth/infant death files for 1995 and 1996, comprising 7,465,858 singleton births and 193,266 twin births. The authors also evaluated effect modification between smoking and hypertension and the effect of a dose-response relation with number of cigarettes smoked daily on abruption risk. Abruption was recorded in 5.9 per 1,000 singleton births and 12.2 per 1,000 twin births. Risk factors for abruption among singleton and twin births, respectively, included preterm premature rupture of membranes (adjusted relative risks (RRs) = 4.89 and 2.01), eclampsia (RRs = 3.58 and 1.67), anemia (RRs = 2.23 and 2.33), hydramnios (RRs = 2.04 and 1.66), renal disorders (RRs = 1.54 and 2.56), and intrapartum fever (>100 degrees F) (RRs = 1.17 and 1.69). Chronic hypertension (RR = 2.38) and pregnancy-induced hypertension (RR = 2.34) were risk factors for abruption in singleton births but not in twin births. Number of cigarettes smoked daily demonstrated a dose-response trend for abruption risk in singletons and twins. Abruption was more likely to occur among smokers with chronic hypertension (RRs = 4.66 and 3.15) and eclampsia (RRs = 6.28 and 5.08). The authors conclude that abruption is twice as likely to occur in twins as in singletons with differing risk factor profiles. This suggests that abruption in twins may result from different pathophysiologic processes.     

Birthweight, preterm births and neonatal mortality in Belgium and the United States

Summary. Belgium is known to have a lesser low birthweight rate and a lower infant mortality rate than the United States. We used previously unpublished data to show that beneath this comparison lies a more complicated picture. Singleton live birth certificates for 1986-67 were analysed. Despite a lower mean birthweight in Belgium (3360 g) than in the United States (3420 g), Belgium had fewer (4.9%) low birthweight infants than the US (5.9%) because of fewer preterm births (4.4 vs. 9.3%). Consistent with the excess of preterm births in the US, the residual distribution of birthweight was smaller in Belgium (2.2% vs. 3.1%). Whereas neonatal mortality was 4.8/1000 in Belgium and 5.6/1000 in the US, birthweight-specific neonatal mortality was higher in Belgium. The challenge for Belgium is to improve the survival of newborns regardless of their birthweight. In the US, the task is to eliminate the excess of small preterm infants.     

Differences between mistimed and unwanted pregnancies among women who have live births

CONTEXT: Mistimed and unwanted pregnancies that result in live births are commonly considered together as unintended pregnancies, but they may have different precursors and outcomes. METHODS: Data from 15 states participating in the 1998 Pregnancy Risk Assessment Monitoring System were used to calculate the prevalence of intended, mistimed and unwanted conceptions, by selected variables. Associations between unintendedness and women's behaviors and experiences before, during and after the pregnancy were assessed through unadjusted relative risks. RESULTS: The distribution of intended, mistimed and unwanted pregnancies differed on nearly every variable examined; risky behaviors and adverse experiences were more common among women with mistimed than intended pregnancies and were most common among those whose pregnancies were unwanted. The likelihood of having an unwanted rather than mistimed pregnancy was elevated for women 35 or older (relative risk, 2.3) and was reduced for those younger than 25 (0.8); the pattern was reversed for the likelihood of mistimed rather than intended pregnancy (0.5 vs. 1.7-2.7). Parous women had an increased risk of an unwanted pregnancy (2.1-4.0) but a decreased risk of a mistimed one (0.9). Women who smoked in the third trimester, received delayed or no prenatal care, did not breast-feed, were physically abused during pregnancy, said their partner had not wanted a pregnancy or had a low-birth-weight infant had an increased risk of unintended pregnancy; the size of the increase depended on whether the pregnancy was unwanted or mistimed. CONCLUSION: Clarifying the difference in risk between mistimed and unwanted pregnancies may help guide decisions regarding services to women and infants.     

Convenience and the occurrence of births: induction of labor in the United States and Canada.

This paper, using data for the United States and Canada on number of births by day of the week, presents indirect evidence for the widespread incidence of the practice of elective induction. For both the United States and Canada, it is found that substantially fewer births occur on Saturdays, Sundays, and holidays than on weekdays. Controlling for such factors as prenatal care, race, education, legitimacy, birth weight, and time trend strongly suggests that the induction of labor is responsible for the patterns found. The paper concludes by discussing the framework within which the practice of elective induction of labor should be evaluated and justified.     

Unwanted,unwelcome and unborn -- the female fetus

The sex ratio at birth was examined within a population of 68 out of 75 villages in the PHC Malaud, Ludhiana district, Punjab state, India, during 1988-89. Data was obtained from a female medical public health worker and cross checked by home visits and village registers. Observed sex ratios were compared to expected sex ratios of 105 males per 100 females, which were acceptable as a standard by Ramachandra and Deshpande's analysis of hospital births in India in 1964 and other developing and developed countries. Findings showed that the secondary sex ratio at birth was 118.21 in 1988 and 116.68 in 1989. The standard error of proportion (SEP) between the observed and expected was 1.02 in 1988 and 1.01 in 1989. Pooled hospital data on the sex, sex ratio, and SEP of live births was provided for the annual period of 1981-88; the sex ratio in 1988 was 121.80 and the SEP was 0.58. Pooled community data was also presented for the period 1984-88; the sex ratio was 119.20 in 1988 and the SEP was 1.43.. The evidence strongly suggested from the three different sample populations that sex selection and imbalanced sex ratios was a matter of great concern.     

Stability of Retrospective Pregnancy Intention Reporting Among Women with Unwanted Pregnancies in the United States

Maternal and Child Health Journal - Objectives Retrospective assessment of pregnancy intention may be unreliable as women’s perceptions of a past conception can change over time. We compared...     

IUD insertion practices in the United States and Puerto Rico, 1973.

Retrospective reports on IUD insertions during the first 6 months of 1973 were provided by 16,893 physicians residing in the U.S. and Puerto Rico. This was 48.9% of the physicians listed in the master files of the American Medical Association and the American Osteopathic Association as having an interest in obstetrics and gynecology, public health, general preventive medicine, or family practice. Information elicited by interviews with 1% of the nonrespondents mirrored that of the respondents. It is estimated that in the 6-month period there were 810,000 IUD insertions. Regional rates varied from a high of 27.3/1000 in parts of the West to 11.8-12.4/1000 in the Midwest. The rate for the nation was 18/1000. The percentage of nonprivate patients receiving IUDs varied substantially by region, too. 85% of all insertions were do ne by physicians; 6% by paramedical personnel. 90% of the physician-inserted IUDs were by doctors whose primary specialty was obstetrics-gynecology and more than 75% were by doctors engaged in direct patient care. Rates of insertion by individual physicians varied greatly. 1% of the obstetricians-gynecologists averaged more than 8 insertions a week.