There are many types of blood testing that may provide information regarding irregularities that influence your chances of conceiving. Based on, among other factors, your medical history, the regularity of your menstrual cycle and your age, your treating nurse or physician will decide which kind of blood testing is most likely to provide clarity for your situation.
Blood testing may consist of, for example, extensive hormonal testing in case of an irregular menstrual cycle, or an examination of your ovarian capacity (the number of ova left in your ovaries). There is also evidence in your blood if you have ever suffered a chlamydia infection. Women who have suffered from such an infection are more likely to have fertility issues stemming from irregularities with their fallopian tubes.
Blood testing can be used to extensively examine all hormones which have an influence on sperm cell production.
Decreased fertility or infertility in men can only rarely be traced back to a hormonal disorder. Still, in rare cases, it is possible that the brain produces no (or too little) LH and FSH, two kinds of hormones. LH is involved in the production of testosterone, and FSH plays a part in the production of sperm cells.