You have decided you want to become pregnant, or you are seriously considering it. Perhaps you have been trying for a few months, or you want to know where you stand before you begin. In both cases, a blood test can provide valuable information. Good preparation starts before conception.
Why test blood when trying to conceive?
A preconception blood test helps you detect deficiencies or hormonal imbalances early, giving you the chance to address them before pregnancy. Some deficiencies, such as low folate or suboptimal thyroid function, are simple to correct when caught in time but require a few months to address. Other values, like AMH, provide insight into your fertility status so you can make informed decisions about timing. It can also provide reassurance: knowing your values are good lets you approach the process with confidence.
AMH: your ovarian reserve
AMH (anti-Mullerian hormone) indicates your egg reserve: the number of eggs you still have. It is produced by small follicles in the ovaries and declines gradually with age. Important nuances: AMH reflects quantity, not quality. A low AMH does not mean you cannot conceive, but it may mean your fertile window is shorter. AMH can be measured at any point in your cycle, though hormonal contraception can temporarily lower the value. Wait two to three months after stopping the pill before testing.
AMH is particularly informative if you are over 30, have a family history of early menopause, or want to understand whether there is time pressure.
FSH and LH: cycle regulation
FSH and LH work together to regulate egg maturation and ovulation. Measured on cycle day 2-4, they provide insight into your baseline hormonal function. An elevated FSH above 10-12 IU/L may indicate diminished ovarian reserve. An abnormal FSH-to-LH ratio, particularly an elevated LH, can suggest PCOS. The LH surge just before ovulation can also be tracked at home with ovulation tests.
Oestradiol: measuring your baseline
Oestradiol (E2) on cycle day 2-5 reflects your basal hormone production. An elevated early oestradiol above 200-300 pmol/L, like elevated FSH, can suggest the ovaries are working harder to compensate. Oestradiol also plays a crucial role in building the uterine lining, essential for embryo implantation.
Progesterone: confirming ovulation
Progesterone is best measured in the luteal phase, around cycle day 19-22 for a 28-day cycle. A sufficiently high level (typically above 25-30 nmol/L) confirms ovulation has occurred. Without ovulation, fertilisation is not possible. Low luteal-phase progesterone may indicate an anovulatory cycle or insufficient luteal phase. Both situations are treatable.
Thyroid function: essential and often forgotten
TSH is the primary thyroid screening marker. For women trying to conceive, international guidelines recommend TSH below 2.5 mIU/L, stricter than the standard reference range of up to 4.0-5.0. A subclinically elevated TSH can affect conception rates, increase first-trimester miscarriage risk and impact foetal brain development. If TSH is abnormal, also measure free T4. Treatment with levothyroxine is straightforward and effective.
Ferritin and iron: building reserves
During pregnancy your blood volume increases by approximately 50%, requiring substantial iron. Ferritin gives the most reliable picture of your iron stores. Aim for at least 40-50 µg/L before conception. Building iron stores takes three to six months, so start early. Also consider testing haemoglobin to check your current red blood cell levels.
Vitamin D, folate and vitamin B12
Vitamin D is involved in embryo implantation, placental development and immune regulation during pregnancy. A target level of 75-100 nmol/L is often recommended for women trying to conceive. Folate is crucial for early nervous system development; start supplementation at least three months before conception to reduce the risk of neural tube defects. Vitamin B12 works closely with folate in cell division and is especially relevant for women who eat few animal products.
Timing: when to test what
- Cycle day 2-5: FSH, LH, oestradiol (baseline hormones at their most stable)
- Cycle day 19-22: progesterone (confirm ovulation; adjust for shorter or longer cycles)
- Any time: AMH, TSH, ferritin, vitamin D, vitamin B12, folate
Practical tip: you can combine the cycle-independent tests with your day 2-5 blood draw to minimise the number of appointments.
Frequently asked questions
When should I start testing?
Ideally three to six months before you actively start trying, giving you time to address any deficiencies. But testing is valuable at any stage. Some women start with AMH alone to understand their egg reserve, then plan additional tests. There is no wrong moment to gain more insight into your health.
What if AMH is low?
A low AMH can feel concerning, but perspective is important. It reflects egg quantity, not quality. Women with low AMH conceive naturally every day. However, it may mean your fertile window is shorter, adding urgency not to wait too long. Always discuss your AMH with a fertility specialist who can place it in the context of your age, other hormone values and personal situation. A low AMH is not a diagnosis of infertility.
How long should I try before testing?
The general guideline: under 35, further investigation is recommended after twelve months of trying. Over 35, the guideline is six months. With known risk factors such as irregular cycles, endometriosis or a previous pelvic infection, you can test earlier. A preconception blood test can be done at any time, even before you start trying. It is proactive, not panicked.
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