Vitamin A in pregnancy and lactation

The consequences of variations in the supply of vitamin A during pregnancy and lactation, and the means by which vitamin A is transported from mother to foetus and to suckling offspring are summarized, followed by an account of some observations on a rural West African community, with a comment on their possible implications for human requirements. Effects of deficiency on reproductive performance during pregnancySevere deficiency of vitamin A causes infertility, or impaired reproduction, in all vertebrate species which have been studied (Moore, 1957).The early studies on this impairment indicated that although the oestrous cycle is disrupted, and the vagina becomes permanently keratinized, the most characteristic results of deficiency are foetal resorption, stillbirths, and congenital malformations, rather than ovarian dysfunction or failure of fertilization or implantation.The complications of inanition, decreased resistance to infection, and other nonspecific effects of vitamin A deficiency made these observations difficult to interpret, until it was shown that retinoic acid would correct the systemic abnormalities, but failed to support vision and reproduction.In retinol deficient, retinoic acid-fed rats and guinea-pigs, the oestrous cycle and conception seemed normal, but the foetuses were resorbed (Thompson et al. 1964;Howell et al. 1967).The earliest abnormality was necrosis of the junctional zone of the placenta (Howell et al.I 964).Possible defects in steroid hormone production have been investigated, following the observations that in the absence of retinoic acid the reproductive performance of vitamin A deficient female rabbits was improved by progesterone administration (Hays & Kendall, 1956), and that conversion of pregnenolone to progesterone was depressed in retinol deficient, retinoic acid-fed rats ( Junejaet al. 1966).However, neither oestrone nor progesterone overcame the defect in reproduction in retinoic acid-fed female rats (Coward et al. 1966; Calaustro & Lichton, 1968; Juneja et al. 1969).Juneja et al. (1969) found that the injection of pregnenolone or of I 7-P-oestradiol in retinoic acid-fed rats reduced the resorption of foetuses, but could not support survival of the pups, or lactation in the dams.Ganguly et al. (1971a, b) observed reduced rates of ovarian secretion of progesterone, 20-a-hydroxypregn-q-en-pone and pregnenolone in pregnant rats maintained on retinoic acid.Abnormalities in the vaginal cell cycle and ovarian function have more recently been observed in retinoic acid-fed rats (Sarada et al. 1977).Thus retinol deprivation probably can cause a disturbance of steroid hormone production, but the extent to which this is responsible for the overall impairment in reproductive capacity is not entirely clear.