Timing effects of prenatal alcohol exposure on specific developmental endpoints

Prenatal alcohol exposure data were collected in 2-week day-by-day drinking histories obtained at each prenatal visit. Because the number and timing of the prenatal visits varied from subject to subject, an attempt was made to estimate alcohol consumption where the data were missing. Alcohol consumption for each week of gestation was estimated for each subject by hierarchical linear modeling (HLM). This method allows one to model patterns of change across time for each individual. HLM enables the researcher to construct a growth curve for each individual based on the observed data available for that individual, the individual's score on the parameters known to be related to that growth curve, and the data available from other subjects. Three parameters were used in constructing the growth curves for this study: maternal age at the time of conception, the Michigan Alcohol Screening Test (Selzer, 1971) and number of cigarettes smoked per day during pregnancy. Nonparametric regression analyses and HLM both identified a cubic function as the best fitting model. The cubic function was used to estimate AA/day data. Results showed that HLM provides estimates of early gestational exposure that make it possible to detect alcohol related developmental defects that would otherwise not be seen due to small sample size. Postnatal growth was primarily related to alcohol exposure during the later part of gestation, while dysomorphology related to early gestation alcohol exposure. Several cognitive measures were specifically related to late pregnancy exposure, including mental rotation and magnitude estimation reaction time; however, visual expectancy reaction time during infancy was related to early alcohol exposure. Whereas the visual expectancy assessed in infancy is a very fundamental cognitive skill, mental rotation and magnitude estimation are more complex and require multiple mental operations. Behavioral problems were generally related to exposure late in pregnancy, with the exception of attention deficits. Although there appear to be adverse effects on attention from late gestation exposure, some aspects of attention are also affected by early alcohol exposure.