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example, one study defined gestational age in completed weeks as estimated from LMP when it was available, imputed gestational age if the month and the year were recorded, but had to rely on clinical estimates in 4 to 5 percent of the cases and had to eliminate from the calculations birth certificates with missing data (2 percent of white infants, 2.7 percent of African American infants, and 3.6 percent of Hispanic infants) (Alexander et al., 2003). These proportions will change in the coming years as more states begin to record best obstetric estimates and the rate of clinical use of early ultrasound to date pregnancies increases.

Clarifying Mortality Rates

The decentralized system for the reporting of vital statistics in the United States has made it difficult to compare state-to-state variations in preterm birth, fetal death, and infant mortality rates (Martin and Hoyert, 2002). In addition to variations in the reporting of gestational age on birth certificates, state requirements for the reporting of fetal deaths vary. There are also regional differences in the rates of underreporting of fetal deaths and missing data on fetal deaths. As attention has shifted toward survival at the lower limits of viability, the definitions of a fetal death and a live birth require attention. How life and death are defined and how very immature and critically ill fetuses are managed at delivery may have important effects on a number of recent trends, including rising preterm birth, neonatal and infant mortality rates, and decreasing fetal death rates.

Less attention has generally been paid to fetal deaths than to neonatal and infant deaths. Approximately 16 percent of all pregnancies end in the death of the fetus (Martin and Hoyert, 2002; Ventura et al., 2001). Fetal death generally includes spontaneous abortions, miscarriages, and stillbirths. The majority (more than 90 percent) of fetal deaths occur in the first 20 weeks pregnancy; 5 percent occur at 20 to 27 weeks gestation; and 2 percent occur late in pregnancy; that is, after 27 weeks gestation. The greatest decrease has been in fetal deaths after 27 weeks gestation. States have different requirements on the data on fetal deaths that must be reported; some require gestational age (gestational age at or beyond 16 weeks, 20 weeks, or 5 months), some require birth weight (birth weight at or above 350, 400, or 500 grams), and some require both gestational age and birth weight criteria. Missing data regarding initiation of prenatal care vary from 17 percent of the records of fetal deaths at 20 to 27 weeks of gestation to 11 percent of fetal deaths beyond 27 weeks of gestation and 2.8 percent of live births.

The possibility exists that changing practices in the categorization and reporting of live births and fetal deaths have contributed to falling fetal death rates and rising preterm birth and infant mortality rates in the United



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