Investigations for infertility usually start after one year of inability to conceive, as stated in the definition. However, in a situation where a woman is more than 35 years, investigation for infertility may begin after six months as the woman does not have the luxury of time that a younger woman has.

The investigations requested for couples with infertility depend on the suspected cause following evaluation by medical experts. These investigations are targeted towards specific causes. The following are some of the investigations which couples suffering infertility may be requested to do.

A. Hormonal Tests

This is commonly done to investigate possible hormonal causes of infertility in females. Below are some of the hormones usually tested for:

1. Follicle stimulating hormone (FSH): This stimulates the ovary to produce eggs and for the eggs to mature to the point where ovulation is possible. When the level of this hormone is lower than necessary for the ovaries to function optimally, eggs may not develop during that cycle or develop and get arrested at certain stage of development. When it is too high, it may indicate that the ovary is not working well.
2. Luteinizing hormone – This hormone stimulates ovulation from mature follicles and progesterone production after ovulation. It works together with FSH. When the level is lower than the normal range, there may not be ovulation and eggs may not be released for fertilization that month. When the level is higher than normal, it may indicate a problem at the level of the ovary and may be responsible for excess androgen production by the ovaries.
3. Progesterone – This test is usually done on day 21 of the menstrual cycle. This is the period its level is supposed to be at the peak if ovulation has occurred in that cycle. It is used to test for ovulation during a menstrual cycle. If ovulation has occurred in a cycle, the level of this hormone will be within normal range; if not, it will be below normal. 
4. Prolactin – This hormone stimulates milk production. There is a level it should not go beyond in non-pregnant and non-lactating women. If it goes beyond the normal, it usually inhibits ovulation, and this subsequently affects menstruation. High level of this hormone may manifest as milk discharge from the breast when the woman is not breastfeeding. Some women with high level of the hormone may not have breast milk discharge.
5. Thyroid hormones – These hormones have several functions in the body. In relation to reproduction, normal levels allow the system to function normally. Low level of the hormones may affect ovulation and menstrual cycle by stimulating excess prolactin production. 
6. Oestrogen – This hormone is produced by the growing follicles in the ovaries. Normal level indicates that there are adequate follicles in the ovaries. When its level is sub-optimal in a reproductive age woman, it may indicate that the woman is in the menopausal or peri-menopausal period. In women not at the age of menopause (40 years and above), it may signify ovarian failure.
7. Testosterone – This is a male hormone. It is of the family of hormones called androgens. It is present normally at a lower level in women than men and it is responsible for sexual drive and pubic / axillary hair growth. When this hormone level is higher than normal, the affected woman experiences both menstrual and fertility problems.

B. Tests Involving The Reproductive Tract

Aside hormonal level in women, other investigations that may be necessary for infertility include: checking the patency of the: (a) cervix, (b) uterus, and (c) fallopian tubes. This is to ensure that there is no obstruction to sperm movement on its journey to meet the egg for fertilization. This may be done in two ways: 

1. Hysterosalpingogram (HSG) – This investigation uses dye to outline the cervix, uterus and the two tubes and x-ray to view the outlined channels. After injecting the dye through the cervix, several x-rays are taken to trace the path of the dye.

When the tubes are patent, the dye will move from the cervix to the uterus and to the tubes, to spill into the pelvis at the lower end of the tubes. When this is the case, the tubes are adjudged patent. When the dye does not spill into the pelvis through the tubes, it may be that: 

1. The tube(s) may have been blocked by prior injury from infection or fibroid blocking the entrance of the tube(s);
2. The tubes may not be blocked really but may prevent the dye passing through by going into spasm due to pain experienced by the woman during the procedure;
3. The uterine cavity or the cervix may be blocked by scar tissue following previous injuries from childbirth or abortion, preventing the dye from reaching the tubes. Sometimes, it may be difficult to distinguish between the previous two but the third is almost always obvious on the HSG film. This is the reason a woman with seemingly blocked tubes on hysterosalpingogram may be required to go through another procedure known as laparoscopy and dye test, to confirm this. 

2. Laparoscopy and dye test – This procedure allows real time visualization of the spillage of the dye through the tubes as it is being injected through the cervix. The procedure is done under anaesthesia, so that the patient will not feel pain.

As tubal spasm due to pain is circumvented through anaesthesia, failure of dye to spill through the tubes may be diagnostic of actual tubal blockage if the cervix and the uterus have been adjudged patent by previous HSG study.