(CDC 1995; Waitzman et al. 1994). The lifetime per-patient cost for spina bifida alone was estimated at $250,000, and the total annual cost for all surviving infants with spina bifida in the United States was $200 million (Sever et al. 1993). A recent study reported that the total lifetime costs for persons born in 1996 with mental retardation, autism, or cerebral palsy will be $47 billion, $4.9 billion, and $12 billion, respectively (Honeycutt et al. 1999). Major developmental defects are the fifth leading cause of years of potential life lost (YPLL) (CDC 1987). For comparison, loss attributed to heart disease before age 65 is 1,600,265 YPLL, loss attributed to cancer is 1,813,245 YPLL, and loss attributed to major congenital anomalies is 694,715 YPLL (CDC 1987).

Those major developmental defects represent only one class of the most socially and medically recognized developmental defects. Several other classes are identified below. Their prevalence has been harder to estimate. To begin with, at least one minor structural defect (e.g., preauricular sinus and syndactyly for toes 2-3) has been identified in 14.1% to 22.3% of live-born infants, a frequency that is 5 to 7 times higher than that for major defects (Leppig et al. 1987). The less-recognized defects are of lesser clinical and cosmetic importance, and the estimate of their birth prevalence varies considerably because of substantial differences in definition and detection and the lack of a national systematic database for this information.

Another class is made up of functional deficits—that is, deficits that are not accompanied by an overt structural defect but are expressed in a variety of ways ranging from delays in growth to deficits in behavioral and neurological development. Many of these deficits are only recognized in infancy or later in childhood (e.g., attention deficit hyperactivity disorder and dyslexia). Developmental defects with reproductive consequences might not be detected until much later. Finally, there is evidence of some mid-life health conditions (e.g., heart conditions) correlating with abnormal birth status (e.g., low birth weight) (Barker 1999). The costs and years of life lost have not been estimated for these more subtle developmental defects among live-born infants.

A further expanded view of developmental defects is gained by examining all pregnancy outcomes (Table 2-1), not only live-birth outcomes. The most common type of outcome in humans is early-pregnancy loss shortly after implantation (Zinaman et al. 1996; Wilcox et al. 1999). That occurs in 20-30% of pregnancies. Many of those losses are difficult to detect and enumerate because they occur prior to clinical recognition of the pregnancy. Spontaneous abortions of clinically recognized pregnancies (generally starting in the 8th week after the last menstrual period) occur in 10-20% of pregnancies (Hatasaka 1994), also a high frequency. Thus, these two categories dominate all other defects. In 40-50% of the spontaneous abortions examined, some type of chromosomal aberration was found, most frequently an extra or missing chromosome (Jacobs and Hassold 1995). Many chromosomally abnormal embryos have anatomical malformations. Fetal deaths (after 20 weeks of gestation) and stillbirths occur in 1-4% of preg-

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