Zinc deficiency can restrict growth in young children, but controlled trials of zinc supplementation during pregnancy in humans have not demonstrated steady effects on weight at birth and/or duration of gestation. The studies who had identified a positive effect of zinc supplementation on fetal growth were conducted on low-socioeconomic populations or in countries where diet and living conditions are improving or in-migrant groups in industrialized countries. Studies conducted either on populations with negligible risk of zinc deficiency or in those suffering from multiple and severe nutritional deficiencies, there were no effects found. The possible confounding factors explaining the contradictory results might include the age of pregnant women, any digestive disorders, any other nutritional deficiencies, phytates or other factors affecting bioavailability, duration of zinc supplementation and compliance with supplements.

Few studies of supplementation of zinc were performed on infants who were born small for their gestational age or preterm. A positive effect on their growth was seen in these studies. A study of zinc supplementation in pregnancy has reported reduced risk of diseases such as diarrhoea or impetigo in small-for-gestational-age but not for preterm infants. Another second study has demonstrated reduced mortality in small-for-gestational-age infants. It is concluded that trials of zinc supplementation during pregnancy do not provide definite evidence for a beneficial effect of zinc supplementation in spite of the experimental evidence that deficiency of zinc can retard fetal growth or shorten the length of pregnancy.

Yet, early supplementation of zinc in low birth weight or small-for-gestational-age infants has revealed an effective improvement in growth. This suggests a prenatal reduction or insufficient zinc intake should support catch-up growth postnatally in such infants.

Source: Castillo-Durán C, Weisstaub G. Zinc supplementation and growth of the fetus and low birth weight infant. J Nutr. 2003 May;133(5 Suppl 1):1494S-7S. doi: 10.1093/jn/133.5.1494S. PMID: 12730451.