Fetal death rate is an important marker of quality of health care in developed countries. Although the fetal death rate has declined over the last three decades in the United States,1 there continues to be a disparity with black women having higher incidence of fetal death compared with their white counterparts.2 Little is known about the cause for this disparity, but Taylor et al have suggested that it is most likely multifactorial.3 Several studies have established the association between lack of prenatal care and increased fetal death rate regardless of race.4–9 However, a cause-and-effect relationship between lack of prenatal care and increased fetal death rate has not been clearly established. Moreover, it is not clear how much of the disparity in fetal death rates between blacks and whites is due to lack of prenatal care per se or the high frequency of associated medical and obstetric high-risk conditions seen among those with no prenatal care. Therefore, the purpose of this large population-based cohort study was to determine the impact of prenatal care in the United States on fetal death in the presence and absence of obstetric and medical high-risk conditions, and to explore the role of these high-risk conditions in contributing to the disparity in fetal death rates between blacks and whites.
MATERIALS AND METHODS
The study was approved by the institutional review boards at the University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School-Robert Wood Johnson University Hospital. Data were derived from the national perinatal mortality sets for 1995–1997 in the United States assembled by the National Center for Health Statistics.10 These data are based on live births and fetal and infant deaths up to 1 year, registered in all states and the District of Columbia. Analysis was restricted to fetal death and live births that occurred at or beyond 24 weeks' gestation. Gestational age (in completed weeks) was calculated as the interval between the date of delivery and the date of last normal menstrual period (LMP). Records with missing date of LMP but with valid month and year of the LMP had gestational age imputed.11 When the LMP date was missing or when the LMP-based gestational age was inconsistent with birth weight, a clinical estimate of gestational age was used instead (in about 5% of records).12 These imputations and replacements of gestational age by clinical estimates were performed by the National Center for Health Statistics. All medical and obstetric high-risk conditions were recorded using a check-box format on birth and death certificates indicating the presence or absence of the condition.13 Multiple births, fetuses, and infants with congenital or chromosomal abnormalities, missing data on gestational age, gestational age below 24 weeks, or birth weight below 500 g, and those with missing data on prenatal care were excluded.
Fetal death was defined as a fetus without any signs of life at birth. We chose 24 weeks as a threshold because fetal viability starts at this gestational age. Because the exact timing of fetal death is unknown in most cases, we used gestational age at delivery as a proxy for time of death.14 For the purpose of this analysis, prenatal care was considered present if there was at least one prenatal visit during the course of pregnancy. The analyzed high-risk conditions included maternal anemia (maternal hemoglobin less than 10.0 g/dL or a hematocrit less than 30% during pregnancy), intrapartum fever (greater than 100F), preterm premature rupture of membranes (over 12 hours from rupture of membranes to the onset of labor), hydramnios, diabetes (all classes), chronic hypertension (persistent blood pressures greater than 140/90 mmHg before pregnancy or before 20 weeks' gestation), pregnancy-induced hypertension (diagnosed after 20 weeks' gestation and defined as a rise of 30 mmHg in systolic or 15 mmHg in diastolic blood pressure during pregnancy), renal disease, placental abruption, placenta previa, bleeding (unknown cause), fetal growth restriction (birth weight less than the tenth percentile for gestational age), Rh sensitization, post-term pregnancy (42 weeks or longer), and history of prior preterm (less than 37 weeks' gestation) or small-for-gestationalage infant.
Rates of fetal death (per 1000 births) were computed for women with and without prenatal care, and unadjusted relative risks with 95% confidence intervals were derived as measures of effect. Adjusted relative risks were estimated with adjusted odds ratios derived from multivariable logistic regression models. Covariates considered for adjustment in the regression models included the obstetric and medical high-risk conditions, as well as maternal age, gravidity, maternal education (less than 12, 12, 13, or more years of schooling), marital status (unmarried or married), smoking, and alcohol use in pregnancy. Confounders that changed the unadjusted relative risks by at least 10% were retained in the models for adjustment. Adjusted population attributable risks (%) were calculated for each high-risk condition in the presence and absence of prenatal care.15 The data were analyzed using the SAS system (SAS Institute, Cary, NC).
During the years 1995–1997, there were 11,958,515 pregnancies in the United States resulting in either fetal death or live birth. Of these, the following groups were sequentially excluded: multiple births (n = 338,489), congenital or chromosomal abnormalities (n = 648,278), missing data on gestational age or gestational age less than 24 weeks or birth weight below 500 g (n = 196,117), and missing data on the presence or absence of prenatal care (n = 215,554). From this latter group, 213,100 were live births, and 2454 (1.1%) were fetal deaths. After these exclusions, a total of 10,560,077 singleton births at or beyond 24 weeks (including all races) remained for analysis. Among all races, there were 29,469 fetal deaths (fetal death rate 2.8 per 1000) and 120,421 (1.1%) mothers with no prenatal care.
Blacks were 3.3 times more likely to have no prenatal care compared with whites (2.7% versus 0.84%). Table 1 shows the fetal death rates for the overall population (all races) and also for blacks and whites, separately. Fetal death rates were higher for blacks as compared with whites in the presence (4.2 versus 2.4 per 1000) and absence (17.2 versus 12.5 per 1000) of prenatal care. Lack of prenatal care increased the (adjusted) relative risk for fetal death 2.9-fold in blacks and 3.4-fold in whites. An analysis of the number of prenatal care visits and the risk of fetal death showed an inverse dose-response relationship for up to 14 visits for both blacks and whites (Figure 1). Figure 2 illustrates the relationship between fetal death rate and gestational age at delivery. Lack of prenatal care was associated with significantly higher fetal death rates for both blacks and whites, especially for births occurring after 30–32 weeks' gestation. Among women with prenatal care, the degree of reduction in fetal death rate was somewhat greater in whites for births occurring after 36 weeks' gestation. Figure 3 illustrates the proportional distribution of cumulative fetal death throughout gestation. Fetal death occurred earlier in gestation among those without prenatal care. Regardless of prenatal care status, fetal death occurred earlier in gestation in blacks compared with whites.
At least one high-risk condition was present in 38% of blacks and 28% of whites. Table 2 illustrates the rates, as well as the adjusted relative risks, for fetal death in the presence of high-risk conditions. Lack of prenatal care was associated with increased risk for fetal death in the presence of all high-risk conditions.
Fetal growth restriction and placental abruption were the two largest contributors to fetal death in the presence (adjusted attributable risks of 18.8% and 8.2%, respectively) and absence of prenatal care (adjusted attributable risks of 9.2% and 13.3%, respectively). The attributable risks for the other high-risk conditions in the presence of prenatal care ranged from 0.1% to 1.5%, and in the absence of prenatal care from 0.1% to 3.1%. These attributable risks were similar between blacks and whites. Table 3 illustrates rates and adjusted relative risks for fetal death for blacks and whites. Among women with no prenatal care, the greatest relative risks for fetal death were in the presence of placenta previa, diabetes, bleeding of unknown cause, and pregnancy-induced hypertension for blacks; and bleeding of unknown cause, placenta previa, diabetes, and maternal anemia for whites. Among those with prenatal care, the black–white fetal death rate disparity persisted for all high-risk conditions with the greatest disparities observed for maternal anemia, diabetes, pregnancy-induced hypertension, and renal disease.
We want to emphasize that one of the strengths of this study is the large number of included patients based on national data. However, a possible weakness may be related to underreporting of fetal death in some states, especially in gestational ages less than 28 weeks, or variations in reporting from state to state. This heterogeneity may have somewhat biased the results of this study, but because most differences in fetal death rates were observed after 28 weeks' gestation, the bias is likely to be minimal. Another possible limitation of our study is the underreporting of certain risk factors and complications,16,17 and the unavailability of certain important information in the vital statistics data, including geographic inaccessibility to prenatal care by rural women or unavailability of obstetricians in certain areas of the country. Risk factors such as maternal depression, poor weight gain, long work hours, or illicit drug use are factors known to be associated with lack of prenatal care and subsequent fetal death, but such risk factors were unavailable in the vital statistics data set. Therefore, such confounding factors may be the cause(s) of fetal death, and lack of prenatal care may be a marker for these high-risk behaviors, lifestyles, and conditions. In this study, we restricted our analysis to potentially viable pregnancies delivered at or beyond 24 weeks' gestation and excluded those with birth weights less than 500 g because many of these may represent abortions. We did not include pregnancies delivered between 20 and less than 24 weeks' gestation because many of these pregnancies may have been already excluded, having birth weights less than 500 g. In addition, the registration of births in pregnancies with borderline viability is unreliable.18
Several studies have examined the epidemiology of fetal death, and various high-risk factors have been identified including lack of prenatal care, black race, third-trimester bleeding, chronic hypertension, preeclampsia, diabetes mellitus, Rh isoimmunization, maternal anemia, maternal age greater than 35 years, and history of adverse perinatal outcome.1–9 Some of these high-risk factors can be treated and controlled, but many may not be preventable. Lack of prenatal care is a theoretically preventable factor and, therefore, it is extremely important to know if patients with no prenatal care are at increased risk because of lack of prenatal care per se or because of increased incidence of associated high-risk conditions among women with no prenatal care. Our study suggests that lack of prenatal care is associated with increased fetal death rate in the presence as well as in the absence of various high-risk conditions, implying that there may be a cause-and-effect relationship between prenatal care and fetal death rate. Although the benefit of prenatal care in reducing fetal death in blacks and whites was of a similar magnitude for most high-risk conditions (Table 3), the overall disparity in fetal death rates between blacks and whites persisted even in the presence of prenatal care (4.2 versus 2.4 per 1000, respectively). The excess fetal death rate between blacks and whites among those who sought prenatal care was 1.8, whereas among those without care was 4.7 per 1000 births (Table 1). Thus, prenatal care narrowed the disparity in fetal death rate among blacks by 62% compared with whites. This observation is in agreement with previous studies that have suggested that prenatal care reduces fetal death rate and significantly narrows the disparity in pregnancy outcomes between blacks and whites.3,19 Because blacks were 3.3 times more likely to have no prenatal care compared with whites, increased prenatal care participation, especially among blacks, should be expected to decrease fetal death rates. However, the persistence of disparity in fetal death rates even in the presence of prenatal care suggests that more comprehensive strategies, other than prenatal care in its current form, are required to achieve equity between blacks and whites. One such strategy may be future application of condition-specific prenatal care according to the underlying high-risk condition to prevent fetal death.
Previous studies have examined the timing and number of prenatal care visits to define accuracy of prenatal care.20 In this study, prenatal care was considered present if there was at least one prenatal visit. The rationale for this definition is based on the finding that a single prenatal visit, compared with no prenatal visits at all, is associated with better pregnancy outcomes reflected by a 20% reduction in perinatal deaths, approximately 30% reduction in low birth weight infants, and approximately 50% reduction in preterm births.21 In addition, we found a strong inverse dose-response relationship between the number of visits and fetal death rate, including a beneficial effect of only one visit (Figure 1). Given our definition, lack of prenatal care was associated with increased risks for fetal death to a similar degree for the studied high-risk conditions for blacks and whites, except in the presence of maternal anemia, when the risk for fetal death was much higher among whites with no prenatal care. Determination of the magnitude of the risk for fetal death in the presence of various high-risk conditions may shed some light into the mechanism(s) by which prenatal care might reduce fetal death. The greatest risk reductions for fetal death among women who sought prenatal care were in the presence of placenta previa, vaginal bleeding of unknown cause, diabetes, chronic hypertension, and pregnancy-induced hypertension. Possible explanations for the decreased fetal death rate in the presence of placenta previa or unexplained vaginal bleeding among women with pre-natal care include patient education for early symptom recognition and timely access to appropriate medical facilities when bleeding occurs. The beneficial effects of prenatal care in chronic and pregnancy-induced hypertension may be related to better control of blood pressure, as well as prompt recognition and early intervention in cases of worsening hypertension or preeclampsia. The beneficial effects of prenatal care with respect to maternal anemia and diabetes may be due to appropriate treatments with iron supplementation and blood sugar control, respectively. Another possible explanation for higher fetal death rates among blacks may be lack of use or access to medical care and control of preexisting diseases before conception.
As seen in Figure 3, 50–60% of fetal deaths among those with no prenatal care had already occurred by 32 weeks' gestation, whereas only 30–40% of fetal deaths had occurred among those with prenatal care. This difference suggests that prenatal care was associated with prolongation of fetal life, for both blacks and whites, even among those fetuses that eventually died. As antepartum fetal surveillance is usually initiated after 32–34 weeks' gestation for most at-risk patients,22 it may not be very effective because many fetal deaths occur at earlier gestations. Therefore, antepartum surveillance alone is not enough but should be combined with early prenatal care to have a greater impact. Another important consideration for reducing fetal death is to develop better techniques of surveillance in the settings of fetal growth restriction and abruptio placenta because these two closely related high-risk conditions were the largest contributors (27% combined) to the fetal death pool among patients with prenatal care.
In summary, we conclude that in the United States, prenatal care is associated with fewer fetal deaths in the presence, as well absence, of high-risk conditions for both blacks and whites. Strategies to increase prenatal care participation, especially among blacks, are necessary to decrease fetal death rates. Future studies are needed to identify the factors responsible for the disparity between blacks and whites and also to determine if the beneficial effect of prenatal care in reducing fetal death rate is extended to the newborn period.
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© 2002 The American College of Obstetricians and Gynecologists
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