Rats were trained in shock-induced aggression, free operant avoidance, or were presented with unavoidable shocks. Fighting in response to shock was subsequently measured by intermatching individual animals that had received the three training procedures. The fighting probabilities of animals with histories of avoidance and dominant animals with histories of fighting were higher than the fighting probabilities of non-dominant fighting rats or rats with a history of unavoidable shocks. Animals with higher fighting probabilities disrupted avoidance baselines more than animals with lower fighting probabilities. Control experiments suggested that fighting decrements produced by administration of prior grid-shock were due to the acquisition of behaviors incompatible with aggression.Although fighting elicited by electric shock has obvious respondent characteristics (Ulrich and Azrin, 1962), past experience with fighting and shock has been shown to be related to the frequency of such attacks (Powell and Creer, 1969). For example, single animals presented with inescapable shocks showed decrements in their later shock-induced fighting rates (Powell and Creer, 1969), whereas animals with prior exposure to shock-induced aggression fought at higher rates and more strenuously than did naive animals (Hutchinson, Ulrich, and Azrin, 1965). These data suggest that environmental variables are important determinants of shockinduced aggression. The data also raise the question of the extent to which an incompatible operant might interfere with respondent behaviors, and conversely the extent to which a history of shock-induced aggression might impair the acquisition of such an operant. The experiments of Maier, Seligman, and Solomon (1969), for example, have shown that "inescapable" shocks retard later operant avoidance performance.Several attempts to study the effects of shock-induced fighting on a free-operant baseline and on the acquisition of an operant response have been made by studying the avoidance behavior of paired animals, one or both of which have had avoidance or escape train-

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INTRODUCTION:Preeclampsia (PEC) and fetal growth restriction (FGR) share common pathophysiology of placental insufficiency. In pregnancies complicated by PEC, the incidence of FGR increases significantly. We sought to examine the timing of FGR development in patients with PEC.METHODS:This was a retrospective cohort study of patients with PEC and singleton pregnancy who delivered at 23 weeks or greater. Patients who had been diagnosed with FGR prior to PEC diagnosis, those who were diagnosed with FGR at the same time as PEC, and those who delivered immediately after PEC diagnosis were excluded. Demographics were compared between patients with FGR and those without FGR. We plotted Kaplan-Meier curves for the interval from the diagnosis of PEC to the development of FGR. A Cox proportional hazards model was used to estimate the adjusted hazard ratios (HRs) for FGR. Our IRB approved this analysis.RESULTS:Of 392 patients with PEC, 31 (7.9%) developed FGR. Compared to patients who did not develop FGR, patients who developed FGR were more likely to have early-onset PEC and lower maternal weight and were less likely to have gestational diabetes (P<.05). The incidence rate of FGR increased by 11.6% each week from the PEC diagnosis. Compared to patients with late-onset PEC, those with early-onset PEC had a significantly higher cumulative incidence of FGR (P<.01). The Cox proportional hazards model showed that early-onset PEC was associated with FGR (adjusted HR 4.12, 95% CI 1.19–14.33) compared to late-onset PEC.CONCLUSION:Patients with early-onset PEC had a significantly higher incidence of FGR compared to those with late-onset PEC. There was a high cumulative incidence rate of FGR in patients with early-onset PEC. Patients with PEC should be followed by serial fetal growth ultrasound.

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