The egg that may become your baby a year from now is already maturing today. That process takes around 90 days, and during it the egg draws on exactly the nutrients circulating in your body at that moment. That is why the preconception window, the three months before you try to conceive, is such a valuable time to look at your health.
My take: waiting until the first positive test to think about nutrition is too late. Many deficiencies that can cause problems later in pregnancy are far easier and calmer to correct before conception. A blood test gives you no obligation, but it does give you insight.
Why the three months before conception matter
During this period your body literally builds the foundation for a pregnancy. Several nutrients take time to replenish: iron stores, for example, can need three to six months to recover. By checking where you stand in time, you give yourself room to adjust before it truly counts.
The advice to start folate before pregnancy is standard in the Netherlands for good reason. Thuisarts.nl and the Gezondheidsraad have advised for years to begin folate supplementation at the latest four weeks before conception, and preferably earlier. An early look at your blood values fits exactly into that preventive thinking.
Which blood values matter before conception?
The table below helps you decide what is worth testing, why it matters, and a commonly used target range when trying to conceive. Targets are guidelines, not a diagnosis: always discuss your result with a doctor.
| Blood value | Why it matters when trying to conceive | Commonly cited target |
|---|---|---|
| Ferritin | Reflects your iron stores; blood volume rises sharply during pregnancy | At least 40-50 µg/L |
| Vitamin D (25-OH) | Involved in implantation, placental development and immune regulation | Around 75-100 nmol/L |
| Vitamin B12 | Works with folate in cell division and nerve development | Above roughly 300 pmol/L |
| Folate | Crucial for the formation of the nervous system in the first weeks | Assess with your doctor |
| TSH | Thyroid function affects ovulation and early development | Often below 2.5 mIU/L when conceiving |
Iron and ferritin
Iron deficiency is the most common nutritional deficiency worldwide, and women of reproductive age are at extra risk through menstruation. Ferritin gives the most reliable picture of your iron stores, more reliable than hemoglobin alone. Starting a pregnancy with empty reserves can increase the risk of anemia and fatigue. Because replenishing takes months, this is exactly the value you want to know early.
Vitamin D
In the Netherlands a large share of the population has a suboptimal vitamin D level, especially in winter. A deficiency can be linked to complications such as pre-eclampsia and gestational diabetes. The Gezondheidsraad advises women who want to conceive to take 10 µg of vitamin D daily; a blood test can show whether that dose is enough for you to correct any deficiency.
Vitamin B12 and folate
Folate demonstrably lowers the risk of neural tube defects such as spina bifida, precisely in the first weeks when many women do not yet know they are pregnant. Vitamin B12 works closely with it and is mainly a concern if you eat few animal products. Testing is useful if you doubt whether you get enough through food and supplements.
Thyroid: often forgotten
Your thyroid plays a larger role in fertility than many women realise. International guidelines advise a TSH below 2.5 mIU/L when actively trying to conceive, stricter than the standard reference range labs use. An abnormal value can affect ovulation and early development, so always discuss this with a doctor if you want to become pregnant.
What do you not necessarily need to test?
Not every marker is equally useful in the preconception window. Hormones such as AMH, FSH and LH mainly belong here if you want to know your fertility status or if you have been trying for a while; for pure nutritional optimisation they add little. An extensive thyroid antibody test is usually only relevant if your TSH is abnormal or if there is a family history of thyroid disease. Keep your test focused on what you really want to know, which saves unnecessary draws and interpretation.
Practical timing
The nice thing about the nutrition-focused values is that you can measure them all at any point in your cycle. So you do not have to wait for a specific cycle day: ferritin, vitamin D, B12, folate and TSH can all go into a single draw. Ideally start three to six months before you actively begin trying, so you have time to top up any deficiencies calmly. Plan a possible retest with your doctor, for example after a few months of supplementing, to see whether your values are heading in the right direction.
What do you do with your result?
A preconception blood test is no reason for panic and no guarantee. It gives you a snapshot to act on more precisely: top up a deficiency in time, adjust a dose, or have an abnormal thyroid value investigated further with your GP. See it as calm preparation, not an exam you can fail.
Want a broad picture in one go? The Prenatal Essentials can bundle the nutrients that matter most in this period. If you are mainly curious about your hormonal fertility status, take a look at the Fertility Assessment.
Want to know which hormones belong here and when to measure them? Read on in which blood test when trying to conceive and in our pillar hormone testing in women.
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