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No standards exist for reporting the accuracy and completeness of pregnancy histories created by linking the birth and fetal death certificates for all the deliveries occurring to one woman. To link certificates, analysts use deterministic and/or probabilistic approaches. Errors in linkage occur randomly and non-randomly. Any type of error can cause incorrect estimation of the magnitude of relationships. Methods for assessing linkage correctness are proposed. Analysts can detect errors in linkage by comparing the linkage results with the pregnancy history reported by the mother. The analyst interviews a random sample of women, ascertaining the dates and outcomes (stillbirth or live birth) for their births and, if the linkage used certificates from one state, the state where they occurred. For each woman, he/she then assesses the accuracy and completeness of this linkage by comparing it with her reported pregnancy history. An alternative approach is to chronologically sequence each woman's births. The parity for the most recent birth shows the number of babies born to the same woman and should equal the number of births that the analyst linked. In the absence of maternally reported pregnancy histories, an analyst can use data on the certificates to assess linkage correctness. Although this will show whether the correct number of births have been linked, it provides no information concerning the accuracy of linkages. It may be, however, the most universally applicable way of reporting the completeness of the linkage of deliveries.

To examine the association between interpregnancy interval and low birthweight (< 2500 g), preterm delivery (< 37 weeks' gestation), and inadequate fetal growth, we studied a population-based sample of 23,388 white and 4885 black women at low risk for adverse pregnancy outcomes who delivered their first and second infants in Georgia from 1980 to 1992. We used fetal death and livebirth certificates. The interpregnancy interval was the time from delivery to the woman's next conception. For each pregnancy outcome, we stratified by race and used logistic regression to assess the association between interpregnancy interval and outcome, while controlling for confounders. Intervals < 6 months were observed for 3.7% of white women and 7.0% of black women and intervals > or = 48 months were seen for 16.8% of white women and 24.8% of black women. Results from logistic regression showed that, for both races, interpregnancy interval was associated with low birthweight and preterm delivery. Nearly all of the increased risk occurred in intervals < 6 months or > or = 48 months. The magnitude of the increase in risk associated with these intervals ranged from modest to moderate and was similar for black and white women. Because short interpregnancy intervals are rare and are weak risk factors among low-risk women, efforts to lengthen interpregnancy intervals are unlikely to reduce substantially their rates of adverse pregnancy outcomes.

We used 1.4 million fetal death and birth certificates filed in Georgia between 1980 and 1992 to construct 369,686 chains of two or more reproductive events occurring to the same woman. We evaluated these chains using both information on the certificates and information independently collected in interviews with 1311 women. Overall, 86.6% of the chains had the expected number of events, based on the certificate's information about previous pregnancies. Seventy-nine per cent of the chains had the expected number of events based on the maternal interviews. Consistency between the observed number of events in the chain and the number expected, based either on data from the certificates or from the maternal interviews, was greatest for chains with two or three events. Mothers born in Georgia were more likely to have complete chains than mothers born elsewhere. Among the 551,391 non-linked certificates, 48.7% were the mother's first birth, 40.2% were second or higher-order births to women whose previous pregnancy occurred before 1980, and 11.1% were second or higher-order births to women whose previous pregnancy occurred after 1980. Fetal death and livebirth certificates can be linked to construct pregnancy histories with reasonably low levels of underlinkage and overlinkage.

The birth certificate, the primary tool for population-based surveillance of the condition of infants at birth and maternal status during pregnancy, provides little data about maternal behaviour during pregnancy. To collect data on maternal behaviours that influence pregnancy outcome, we implemented the Pregnancy Risk Assessment Monitoring System in seven states. For this population-based surveillance, new mothers were sampled from birth certificates 2 to 6 months after delivery and contacted by mail; follow-up of nonrespondents was by telephone. Participants completed a 10-page questionnaire. Stratification permitted over-sampling of women with adverse pregnancy outcomes. Among 10,563 women sampled during 1988 and 1989, stratum-specific response rates ranged from 30% to 89%. In 11 of the 28 strata, response rates were greater than 70%. Response rates varied considerably between states. Rates were lower for Black mothers, mothers of low birthweight infants, unmarried mothers and mothers with less than 12 years of education. Active refusal to participate and undelivered mail occurred infrequently. Mail and telephone surveillance of new mothers can yield adequate response rates in selected population groups. Trials of alternative approaches to enhancing response among Black and disadvantaged mothers, such as additional mailings or post-partum in-hospital recruitment, are needed.

Although race and preterm delivery are known to be associated with sudden infant death syndrome (SIDS), the relationships between age at death from SIDS and these factors have not been well described. To examine these relationships, we used linked infant birth and death records for the cohort of 1,204,375 White and 283,776 Black postneonates who were born from 1979 to 1981 in five states: California, Georgia, Missouri, South Carolina and Tennessee. Deaths attributable to SIDS occurred to 1404 White postneonates and to 696 Black postneonates. Although postneonatal SIDS rate among Black infants was twice that of White infants, the relative risk was smaller among infants with gestations of less than 35 weeks. For White postneonates, the median postneonatal age at death sharply declined for gestations from 28-29 weeks to 36-37 weeks and levelled off for longer gestations. For Black postneonates, the results do not support an association between length of gestation and age at death. The findings suggest that practitioners investigating approaches to avert SIDS need to maintain their interventions to an older age among White preterm infants. Researchers investigating the causes of SIDS need to consider the relationship between length of gestation and age at death from SIDS as well as possible developmental differences between White and Black preterm infants.