About 80 per cent of perinatal deaths are associated with low birthweight. Mothers' prepregnancy weight for height is correlated with birthweight, but this is only a crude indication of the close connection between low birthweight and maternal consumption of energy, protein and a range of other nutrients before and around the time of conception. Diet influences follicular growth before ovulation and thus affects ovulatory maturation and the number and quality of ova produced. Immediately after fertilisation diet affects the rate at which ova proceed to first and subsequent cleavages and therefore the size of the subsequent fetus. Diet acts not only directly on follicular and embryonic growth but indirectly by affecting gonadotropin secretion. The endocrine system is sensitive to blood concentrations of amino acids and some vitamins and minerals. Gonadotropin secretion is also depressed by smoking, and by some drugs, poisons and diseases, which may as a result also affect birthweight.