It has long been known that deficiencies of vitamins and fatty acids affect fertility. Among infertility causes which have been neglected for many years, currently quite intensive analyses are carried out as regards the impact of, among others, vitamin D deficiency, abnormal amounts of omega-3 and omega-6 unsaturated fatty acids and other fat-soluble vitamins like vitamin A and vitamin E. Fatty acid and vitamin supplementation without prior detailed diagnosis can not only not help but even impair the possibility of getting pregnant. A vitamin D test should not be performed by means of standard techniques, like ELISA, as they do not measure the total body vitamin D. Consequently, test results for majority of people, including those with normal vitamin D level, will indicate vitamin D deficiency. Vitamin D should be determined by means of chromatography.