Fertility · Before you conceive
What to test before trying to conceive.
The goal of pre-conception blood work is a baseline honest enough to act on. Most of what shows up is a collection of individually minor, collectively decisive readings, and several of the things they report on can still move in the ninety days before conception.
The panel below is the lab map from the Female Fertility guide: six reads on one system. Three things decide what each result means:
- Which day of your cycle it was drawn on.
- Which markers it's read beside.
- Which target it's read against. Several pre-conception targets are tighter bands inside the lab's “normal.”
Six reads on one system
A reasonable baseline for a woman entering active pre-conception planning, read by read:
Ovarian and HPO
Day 2-5 FSH, LH and estradiol. AMH. Mid-luteal progesterone. Total and free testosterone, and DHEA-S.
HPO is the hypothalamic-pituitary-ovarian axis, the signal chain that runs your cycle. The day 2-5 draw reads your reserve and the baseline of that chain. The mid-luteal progesterone is the one blood test that confirms you ovulated.
Thyroid
TSH, free T3, free T4, reverse T3, TPO antibodies.
Thyroid hormones affect ovulation timing, implantation, premature-birth risk and maternal mood, which is why a full thyroid panel is a non-negotiable part of the workup.
Metabolic
Fasting insulin and glucose, HbA1c, HOMA-IR (homeostatic model assessment of insulin resistance).
Even without obesity, dysregulated insulin and glucose disrupt cycling, ovulation and egg health.
Inflammatory
Systemic inflammation is part of the environment an egg matures in, and that environment ages along with the egg.
Nutritional
Vitamin D, ferritin, RBC folate, MMA (methylmalonic acid), omega-3 index.
The nutritional stores conception and pregnancy draw on. Vitamin D receptors sit in ovarian tissue, the endometrium and the placenta, and deficiency is associated with reduced implantation and higher miscarriage risk. Most labs flag deficiency below 20 ng/mL, while the target for reproductive function is 50-70 ng/mL, higher than the general target of 40-60.
Immune and toxin
Added on history
ANA, antiphospholipid antibodies, a urine xenobiotic panel.
These are added on your history, not run on everyone. Circulating autoantibodies can raise miscarriage rates even without a diagnosable disease, and urinary phthalate levels track with IVF outcomes.
This is the core baseline, not an exhaustive list. A clinician will tailor it to your history.
Draw each one on the right day
Estradiol on day 3 and estradiol on day 21 are two different questions, so write the cycle day next to every hormone result.
| Test | When | Why then |
|---|---|---|
| FSH, LH and estradiol | Day 2-5 of your cycle | Later on, the growing follicle's estradiol rises and suppresses FSH, so a late draw reads estradiol high and FSH low |
| AMH | Any day | The small growing follicles make it continuously, largely independent of cycle day |
| Progesterone | About 7 days after ovulation, often day 19-21 | It peaks about a week after ovulation, and an early or late draw reads low even in a strong cycle |
| Fasting insulin and glucose | After an overnight fast | Insulin reads higher after a meal |
Count the progesterone draw from ovulation, not from day 1. Day 21 lands a week after ovulation only in a cycle that ovulates around day 14. In a longer cycle, a day-21 draw comes early and reads low for that reason alone.
When you log your ovulation signs in Merlin, it checks whether a progesterone draw landed in the readable window, about 5 to 9 days after ovulation, before it reads the number. That's what stops a mistimed low progesterone reading as a missed ovulation.
If you were taking progesterone when it was drawn, the number is your dose plus whatever your ovaries made, and it can't confirm or rule out ovulation in either direction. A draw taken off any progesterone answers it outright.
If you're coming off hormonal contraception, start the blood work before you stop. Patterns that pre-dated contraception, such as PCOS, luteal phase deficiency or a tendency not to ovulate, often re-emerge once the hormone clears. While a method is stopping ovulation, a low FSH or progesterone is the method working, not a finding.
Read them beside each other
A lab report answers whether each number sits inside its range. The harder pre-conception questions are whether it's at the tighter target, and what the markers say together.
FSH, LH and estradiol, from the same draw.
FSH means little without the estradiol from the same draw, because a high estradiol falsely suppresses FSH. A day-3 estradiol above about 50 pg/mL sits over the target. Confirm the cycle day first: a late draw reads high for benign reasons. LH is most meaningful as a ratio against FSH from the same day.
AMH, against your age.
AMH reflects the size of the remaining follicle pool. It's a quantity signal, not an egg-quality verdict, and it doesn't predict natural conception either way. A high AMH usually reflects a large pool of small follicles, common in PCOS, rather than extra fertility, so it's read with LH against FSH, androgens and cycle regularity. If yours is low and you're under 40, ask a provider for an ovarian-reserve conversation (antral follicle count, FSH and estradiol). In the 40s, a lower reserve is itself expected for age.
TSH, against the pre-conception target.
The pre-conception TSH target is 2.5 mIU/L or below. In an untreated woman, 2.5 to 4 isn't proven to harm outcomes, but it's the cleaner range to aim for, and worth asking about, especially with thyroid antibodies. Elevated TPO antibodies raise miscarriage and preterm risk even with a normal TSH, and with them the target tightens toward 1-2 mIU/L.
Progesterone, against the day it was drawn.
A mid-luteal progesterone at or above 10 ng/mL, unmedicated and about 7 days after ovulation, confirms ovulation occurred and the corpus luteum is producing well. Between about 3 and 10 points to ovulation from a smaller follicle or a softer luteal phase. Under about 3 suggests ovulation likely didn't occur in that cycle, or the timing was off. An LH strip can't stand in for it: the strip catches the surge that comes before ovulation, and can't confirm the egg was released.
Fasting insulin, beside glucose.
Fasting insulin can climb for years while fasting glucose still looks normal, because the pancreas is working harder to hold glucose where it is. The metabolic piece is worth working on alongside trying, with one exception: blood sugar in the diabetic range makes the pregnancy itself riskier until it's treated, so that one is for a clinician to see before conceiving.
Both partners get the workup
Male factor accounts for roughly 40-50% of infertility, and it's routinely diagnosed late because the assumption is that the female workup is the one that needs running. A semen analysis is a short investment that shifts the whole diagnostic frame if it comes back abnormal.
Merlin's Male Fertility portal reads a semen analysis against the WHO 2021 lower bounds and tracks it over time, with the gonadotropins read next to it.
What to do with yours
- Draw FSH, LH and estradiol on day 2-5, AMH on any day, and progesterone about a week after ovulation.
- Fast overnight before the metabolic draw.
- Write down the cycle day, and whether you were taking progesterone or using hormonal contraception.
- Read each result against its pre-conception target and beside the markers that check it.
- Add the immune and toxin panels when your history calls for them, such as recurrent miscarriage.
- See a clinician before conceiving if your blood sugar is in the diabetic range or antiphospholipid antibodies come back positive.
No results yet? Bring them from anywhere, or order them inside Merlin: Ovarian Reserve - Cycle Day 2-5 ($140) for the early-cycle draw and Ovulation Check - Luteal ($122) for the week after ovulation. Preconception (Female) ($257) adds thyroid with antibodies, vitamin D, ferritin, RBC folate, HbA1c and a blood count to the hormones, and takes two draws: FSH and LH on day 2-5, and progesterone about 7 days after ovulation.
Educational context for your conversations with your licensed healthcare provider, not a diagnosis or a treatment plan. Merlin thinks clinically and never diagnoses.
Merlin does this reading for you. Add your cycle, ovulation and reproductive history, then upload a hormone panel from anywhere, and Merlin reads them together for a pre-conception picture, not just values.
If you don't feel the value of Merlin after paying for your first month, tell us and we'll refund you in full. Monthly Core, once per person, by email within 30 days. The terms
Want to see one first? Watch a real record go from the first read to the Grimoire.