Umbilical cord length has long been investigated as a potential marker of intrauterine events that may place the neonate at risk for future adverse developmental sequelae. Experimentally, significantly shortened cords have been reported in association with prenatal exposure to common drugs of abuse. This study in rats reports the time course of effects on umbilical cord length of a daily maternal ethanol gavage (3,200 mg/kg) from gestational day 6 through termination of pregnancy at either day 17, 18, 19, or 20. A total of 786 fetuses derived from 60 litters were examined. Control fetuses demonstrated a linear increase in umbilical cord length and body weight gain during late gestation, findings that support previous studies. The body weights of the ethanol-exposed fetuses were reduced significantly on all gestational days examined, indicating intrauterine growth retardation, a characteristic of fetal alcohol syndrome. Similarly, acute fetal akinesia as well as long-term sequelae stemming from impaired neurological development would result from the elevated blood ethanol levels achieved in this study. The umbilical cords of ethanol-exposed fetuses were significantly shorter on gestational days 19 and 20 in comparison to their controls, while cord lengths on days 17 and 18 were not shortened significantly. A stretch hypothesis has been proposed suggesting that the degree of fetal activity is the main determinant of umbilical cord length. In rats, there is a physiologic diminution of the volume of amniotic fluid (oligohydramnios) in late gestation (day 19 to term), which restricts fetal movements but does not appear to alter the linear relationships between gestational age and cord length in controls, thus arguing against the stretch hypothesis. However, cord lengths in the ethanol-exposed fetuses plateaued in late gestation, suggesting possible adherence to a stretch hypothesis. This dichotomy is discussed emphasizing fetal growth and activity as well as intrauterine space.
Copyright 2000 Wiley-Liss, Inc.