Trying to conceive and your blood

Blood testing shows how your hormones stand at that moment and whether something is at play that could affect the chance of pregnancy. It is emphatically a snapshot, not a prediction.

What blood cannot do: prove that you can become pregnant, or rule that out. A complete fertility assessment also includes an ultrasound, the pattern of your cycle and, in men, a semen analysis. Those run through your GP or gynaecologist.

What blood testing is good at: finding explanations for an irregular or absent cycle, and showing whether your thyroid and your nutritional status are cooperating.

These tests come up most often when trying to conceive:

• FSH: drives the ripening of the follicles and says something about how your ovaries respond
• LH: gives the signal for ovulation
• Oestradiol: the main oestrogen, which together with FSH and LH shapes the cycle picture
• Progesterone: shows in the second half of the cycle whether ovulation took place
• Prolactin: a raised value can disturb ovulation and cause periods to stop
• TSH: the thyroid influences the cycle and a pregnancy

The moment of the draw matters a great deal. For most hormones, day 3 to 5 of your cycle is customary, counted from the first day of your period. Progesterone, by contrast, is measured about a week before your expected period.

Around a wish to conceive, these tests are useful too:

• folate, which plays a role in the early development of the nervous system
• vitamin D, which often comes out low in the Netherlands
• ferritin, your iron stores, certainly with heavy periods
• vitamin B12, especially with a plant-based diet
• glucose and HbA1c, because sugar metabolism counts

Something special applies to folate: the national advice in the Netherlands is to supplement from the moment you want to conceive up to and including the tenth week of pregnancy. Measuring usually does not change that advice.

Conception is never one person's question. In men, these values can give insight:

• testosterone, total and where needed the free fraction with SHBG alongside
• LH and FSH, which show how the signal from the pituitary is running
• prolactin, which when raised can suppress testosterone

Important: blood testing says nothing about semen quality. That requires a semen analysis, which runs through your GP. For testosterone, have blood drawn in the morning, when the value is highest.