the comprehensiveness of the case population is an important element in assessing the validily and generalizability of the present study. the names of 525 administratively excluded from the WIC prenatal program were omitted from this study. unfortunately very little demographic or motivational information is available about them from the WIC computerized records. the 353 names which had no reason specified for their exclusion were similar racially the wic study population (66.8 percent white excluded group vs 73.6 percent study group)
we are doubtful that most of these 353 names led to an actual massachysetts birth. less than 10 percent of these women errors and out of state moves are the more likely unrecorded realities for these name women do not always inform the wic program of their reasons for discontinuance.nevertheless one cannot rule out of the posssibility that the administratively excluded names may have had specific characteristics which would bias the overall study results.
the birth certificates for 191 women who were in the wic program prenatally could not be located. again little epidemiologic information is available about these women. racially (based on their wic records) they are similar their duration of participation in wic is essentially the same as the wic group one can not rule out the possibility that they may have had specific vharacteristics which would bias the overall result. five wic women with birth certificates were not matched to controls.
overall we estimate that at least 95 percent of the wic prenatal participants population were included in the study which represents the largest and most comprehensive series on wic prenatal participants to date.
establishing the existence and magnitude of a wic program effect also depends critically on the comparability there are inherent limitations to the conclusions that can be drawn from a retrospective cohort study in which the exposure wic group is self selected and the control group is derived by a post-hoc matching procedure. a more ideal randomized case control study would pose serious ethical dilemmas . since many known confounding factors may also be characteristic of the wic or control populations and account for any birth outcome differences noted.
the massachusetts birth certificate do not provide specific information on maternal pre pregnancy weight or height maternal weight again maternal smoking habits or maternal morbidity. any of these factors if unevenly distributed may be sufficient to distort the overall outcome . WIC participants may be more strongly motivated to improve the prenatal health of their future offspring than are the control women. such a motivational difference could cause both an improvement in pregnancy outcome and a desire to enroll in the WIC program. the findings of earlier and more frequent prenatal care visits may be supportive of this view. the increase in prenatal care may also be the cause of the improved birth outcome and not simply another consequence of wic participation the lack of prenatal care improvements among hispanic origin women who show enhanced birth outcomes argues somewhat against this interpretation. the present study design does not lend it self to a study of prenatal care nutrition supplementation or nutrition counseling independently of each other.
although these alternative explanations for the birth outcome difference tend to suggest that the attributed wic program effects may be over-estimated an under-estimation may be just as likely. the wic population could be financially poorer and at greater obstetric risk than their matched controls. all wic participants must have an income under 195 percent of the poverty level while the controls have no restriction on income and presumably some have higher incomes post-hoc analyses reveal that there were more women of hispanic origin in the WIC than the control showing positive sample (906 vs 509) and WIC participants are selected in part on the basis of poor prior obstetrical histories while no such criteria exists for the control group these potential confounding factor in a matched study design would decrease the likelihood of showing positive birth outcomes associated with participation.in summary the massachusetts WIC statewide evaluation project compared the birth outcomes of 4126 WIC prenatal participants and 4126 individually matched controls utilizing public birth and death certificates. results showed that the program appears to be targeted to women at high demographic risk foe poor pregnancy outcomes that overall WIC participation is associated with small improvement in mean birth characteristic larger reductions in marginal pregnancy outcomes and enhanced prenatal care and that these benefits are observe more strongly in higher risk subpopulations and are enhanced with increase duration of participation based on the information available to this study we conclude that participation in the WIC prenatal program is ass