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 States (Martin and Hoyert, 2002). Earlier obstetric intervention when the fetus is not doing well, prompt aggressive resuscitation in the delivery room, and the initiation of neonatal intensive care may save the lives of a few fetuses that formerly died in utero. However, many die within a few days (or weeks of birth). Such efforts may have a significant impact on infant mortality rates (CDC, 2004f ; MacDorman et al., 2005).

If more infants are born alive at the limit of viability but die within days of delivery, thereby contributing to infant deaths, then a small rise in the infant mortality rate should not be viewed with alarm. It might generate a discussion of relative costs (emotional as well as financial) and how limited health care resources should be used, but it is not an indicator of worsening child health. Similarly, intensive prenatal care of high-risk mothers facilitates the detection of fetuses whose adaptive systems become overwhelmed by adverse intrauterine circumstances. An indicated preterm delivery that prevents a fetal death is not an indicator of worsening infant health, even if it does contribute to a higher preterm birth rate

Consideration should be given to using perinatal mortality rates as another child health indicator. Perinatal mortality rates include fetal death rates as well as neonatal mortality rates and would not be expected to change in the two scenarios presented above. However, calculating perinatal mortality rates as an indicator of child health requires that attention be given to how perinatal data are collected and reported, especially regarding fetal deaths.

Attention to the quality of data regarding causes of death could provide insight into the mechanisms of preterm birth as well as the causes of fetal and early neonatal deaths. This approach would require clinicians to vigorously search for causes of death whenever a fetal or early neonatal death occurs. Petersson et al. (2004) found that 11.5 percent of fetal deaths that would have been characterized as unexplained were due to infections with parvovirus, cytomegalovirus, or enterovirus. Other possible causes that should be explored include thrombophilias (e.g., Factor V Leiden), fetomaternal hemorrhage, chorioamnionitis (which would include pathologic examination of the placenta and the umbilical cord), uterine anomalies, umbilical cord or placental anomalies, toxin or drug exposures, and maternal illness (e.g., diabetes, hypertension with or without preeclampsia, thyroid disease, and autoimmune diseases) (Gardosi et al., 2005). Because the most common condition associated with fetal deaths is IUGR (43 percent), research into the mechanisms of IUGR, how to better detect IUGR, and the effect of IUGR on fetal organ systems should be encouraged.

Every avenue that might lead to a better understanding of the causes and mechanisms of preterm birth, fetal and infant mortality, complications of prematurity, health sequelae, and neu-rodevelopmental disabilities should be explored. The costs to infants, their families, and society as a whole are too high to continue to ignore this lack of knowledge.

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