There are many things that can foul your ability to become pregnant and there are some therapies that can greatly increase your chances of becoming pregnant.
The mainstream way is to check the man for sperm count, mobility and morphology. For women they do things like squirt dye into the fallopian tubes to see if they are open. Sometimes this test actually opens the tubes and allows a pregnancy. Another trick they use is Clomid. This drug is given to the man to increase sperm count and to the woman to induce ovulation. Sometimes many eggs are released and several eggs are fertilized. This is how we get quintuplets and sextuplets.
Some of the natural ways I know of increasing the chance of pregnancy:
Progesterone: low progesterone levels are not conducive to pregnancy and this problem is extremely common. Also, a very common reason for miscarriage is low progesterone levels. Even some mainstream specialists know this and treat it to maintain the pregnancy. Unnatural forms of progesterone, like provera, won’t work. Provera will actually make you less fertile and is teratogenic. So when I start a woman on progesterone for PMS or peri-menopausal symptoms, I warn them of the increased risk of pregnancy.
Low carb diet: when you cut back on starchy carbs you unjam some of your metabolic gears; you become more healthy. I warn women when they go on a low carb diet of the increased risk of pregnancy.
Thyroid: if you don’t have enough thyroid hormone you won’t be able to get pregnant. Without enough thyroid hormone you won’t do well during pregnancy. I warn women who start thyroid therapy of the increased risk of pregnancy.
Vitamin D: Low levels of D make it less likely that you will become pregnant. High levels of D predispose to better health in many ways. Healthy women are more fertile. See “Infertility and Vitamin D”.