The Thyroidectomized Pregnant Rat — An Animal Model to Study Fetal Effects of Maternal Hypothyroidism

Abstract

If women are hypothyroxinemic during pregnancy, their children show an abnormally high incidence of behavioral and neurological disorders. The most common problems seen in the children of hypothyroxinemic mothers are: visual disturbances, poor fine-motor coordination, signs of cerebral palsy and lower I.Q. scores (Man et al., 1971; Man and Jones, 1969; Jones and Man, 1969; Nelson and Ellenburg, 1986). Clinically this is a concern because the hypothyroxinemia may occur only during pregnancy and need not be severe to produce these effects; hence, the pregnancy could proceed to parturition with the thyroid disturbance remaining undiagnosed (Jones and Man, 1969). Support for the proposal that normal maternal thyroid function is essential for normal fetal development is provided by the well-established data which show that the developmental deficiencies seen in children suffering from congenital iodine deficiency-in which both the mother and the fetus have a thyroid hormone deficiency-are greater than those resulting only from a fetal thyroid hormone deficiency (Hetzel, 1983; Escobar del Rey et al., 1986; Van Middlesworth and Norris, 1980; Fierro-Benitez et al., 1974; Pharoah et al., 1981). Furthermore, if supplemental iodine is given to iodine deficient pregnant women after the fifth month of gestation (Fierro-Benitez et al., 1972), the iodine does not prevent significant neurological impairment. These data emphasize the importance of normal maternal thyroid hormone production, particularly during the first one-half of gestation.