After a miscarriage, most women receive one of two responses from their doctor.
If it is a first loss, they are told it was likely chromosomal, that it is very common, and that they should try again when they feel ready.
If it is a second or third loss, they may be referred for investigation a panel of tests designed to identify a cause.
But here is what that standard panel almost always misses.
The conventional recurrent miscarriage workup even the one offered by specialist clinics covers perhaps half of the known, modifiable causes of pregnancy loss. The other half goes uninvestigated. Not because the tests do not exist. Not because the evidence is lacking. But because the standard protocol has not kept pace with the research.
This post is the complete picture. Every blood test that should be part of a thorough miscarriage investigation what it measures, why it matters, and how to request it.
WHY INVESTIGATION MATTERS EVEN AFTER ONE LOSS
The conventional threshold for investigation is three consecutive miscarriages. Many clinics now investigate after two.
But the biology does not change based on how many losses a woman has had. A modifiable cause present after one miscarriage is equally present after three and three losses means three more rounds of physical recovery, emotional devastation, and time.
If you have had one miscarriage and something feels wrong if your instinct tells you this was not just bad luck you are entitled to ask for investigation. A compassionate, thorough practitioner should be willing to begin at least a partial workup after a single loss, particularly if there are other clinical features that suggest an underlying cause.
You do not have to wait for three.
THE COMPLETE INVESTIGATION. MARKER BY MARKER
CATEGORY 1: IMMUNE AND CLOTTING MARKERS
These are the markers most likely to be included in a standard recurrent miscarriage panel but even here, the standard panel is often incomplete.
Antiphospholipid Antibodies
Antiphospholipid syndrome (APS) is the most important treatable cause of recurrent miscarriage. It is present in approximately 15-20% of women with recurrent pregnancy loss and is associated with small clots in the placental vessels that interrupt blood supply to the developing embryo.
The full antiphospholipid antibody panel includes three separate tests and all three must be tested to avoid missing the diagnosis:
- Lupus anticoagulant
- Anticardiolipin antibodies (IgG and IgM)
- Anti-beta-2-glycoprotein-I antibodies (IgG and IgM)
A single positive result must be confirmed on repeat testing at least 12 weeks apart to meet diagnostic criteria. Many women are told their antiphospholipid test was negative when only one of the three antibodies was tested.
Ask specifically: "I would like the full antiphospholipid antibody panel including lupus anticoagulant, anticardiolipin antibodies, and anti-beta-2-glycoprotein-I antibodies."
Inherited Thrombophilia Screen
Inherited thrombophilias genetic conditions that increase clotting tendency are associated with recurrent miscarriage, particularly second trimester losses and placental complications.
A full thrombophilia screen includes:
•Factor V Leiden mutation
•Prothrombin gene mutation (Factor II G20210A)
• Protein C activity
•Protein S activity
• Antithrombin III activity
• MTHFR gene variants (C677T and A1298C)
Not all of these are associated with equal miscarriage risk, and the evidence for treatment varies. But knowing your thrombophilia status gives both you and your doctor critical information for managing future pregnancies.
Natural Killer Cell Testing
Uterine natural killer (uNK) cells are specialised immune cells in the endometrium that play a critical role in placental development and immune tolerance of the embryo.
Abnormalities in uNK cell number or activity are found in a significant proportion of women with recurrent implantation failure and recurrent miscarriage — and are almost never tested in standard investigation.
Peripheral blood NK cell testing is available and gives an indication of systemic NK cell activity, though endometrial biopsy for uNK cell assessment is more definitive. This investigation is typically offered through specialist reproductive immunology clinics.
If you have had recurrent miscarriage with no identified cause, NK cell investigation is worth pursuing through a specialist referral.
Thyroid Antibodies
TPO antibodies and thyroglobulin antibodies should be tested in every woman with recurrent miscarriage regardless of TSH.
As covered in this series, thyroid autoimmunity increases miscarriage risk independently of thyroid function. A woman with completely normal TSH and elevated TPO antibodies has a significantly higher miscarriage risk than a woman with normal TSH and negative antibodies.
This is one of the most evidence-based and most consistently missed investigations in recurrent miscarriage workup.
Optimal: TPO antibodies < 15 IU/mL, TgAb < 20 IU/mL.
ANA . Antinuclear Antibodies
ANA testing screens for systemic autoimmunity conditions including lupus and other connective tissue diseases that are associated with pregnancy loss. A positive ANA warrants further investigation to identify the specific antibody pattern and assess clinical significance.
CATEGORY 2: HORMONAL MARKERS
Full Thyroid Function Panel
Beyond antibodies, a complete thyroid assessment includes TSH, Free T4, and Free T3.
The fertility-optimal TSH range is 1.0-2.5 mIU/L. A TSH between 2.5 and 4.5 mIU/L normal on a standard panel is associated with increased miscarriage risk and should be discussed with your doctor in the context of recurrent loss.
Day 21 Progesterone
Progesterone is essential for maintaining early pregnancy. A Day 21 progesterone below 30 nmol/L suggests suboptimal luteal phase function even if it is above the standard threshold of 16 nmol/L used to confirm ovulation.
Women with recurrent miscarriage and low-normal progesterone should discuss luteal phase support vaginal progesterone from ovulation or a positive pregnancy test with their doctor. The evidence for progesterone supplementation in women with a history of miscarriage and low progesterone is growing and it is a low-risk intervention.
Prolactin
Elevated prolactin impairs luteal phase function and early pregnancy maintenance. It should be tested in a fasted, rested state and repeated if elevated on first testing.
Fasting Insulin and HOMA-IR
Insulin resistance is associated with higher miscarriage rates in women with and without PCOS. It contributes through elevated androgens, impaired endometrial receptivity, and systemic inflammation.
Fasting insulin with HOMA-IR calculation should be part of every comprehensive miscarriage investigation it is almost never included in standard panels.
CATEGORY 3: NUTRITIONAL AND METABOLIC MARKERS
These are the markers most consistently absent from standard miscarriage investigation and among the most modifiable.
Homocysteine
As covered in the previous post in this series, elevated homocysteine is independently associated with recurrent miscarriage through multiple mechanisms egg damage, embryo methylation impairment, endothelial toxicity, and prothrombotic effects.
Optimal homocysteine for fertility: < 7.0 µmol/L.
Standard lab range: < 15 µmol/L.
A homocysteine of 10 would not be flagged. It is not optimal. Request it fasting.
Active B12
B12 deficiency is one of the most common causes of elevated homocysteine and active B12 (holotranscobalamin) is a significantly more sensitive marker of B12 status than total B12.
Many women with B12 deficiency have a total B12 that appears normal only active B12 reveals the functional deficiency.
Optimal active B12: > 80 pmol/L.
Serum Folate
Folate is essential for DNA methylation and neural tube development. Low folate is associated with both miscarriage and neural tube defects.
Optimal serum folate for preconception: > 20 nmol/L significantly higher than the standard laboratory threshold.
MTHFR Genotyping
If homocysteine is elevated or folate supplementation has not produced the expected response, MTHFR genotyping identifies whether a genetic variant is impairing folate metabolism.
Women with MTHFR variants should take methylfolate rather than folic acid.
Vitamin D
Vitamin D deficiency is associated with impaired implantation, endometrial immune dysregulation, and early pregnancy loss. It is one of the most straightforward markers to correct and one of the most consistently missed in miscarriage investigation.
Optimal 25-OH vitamin D: 100-150 nmol/L.
Ferritin
Severe iron deficiency impairs the mitochondrial function and oxygen-carrying capacity needed to sustain early pregnancy. Ferritin should be assessed with the fertility-optimal range of 70-120 µg/L in mind not just the standard laboratory threshold of 15 µg/L.
CATEGORY 4: INFLAMMATORY MARKERS
hsCRP, High Sensitivity C-Reactive Protein
Systemic inflammation impairs implantation, endometrial receptivity, and early placental development. An hsCRP above 1.0 mg/L in the context of recurrent miscarriage warrants investigation for underlying inflammatory drivers endometriosis, gut dysbiosis, autoimmunity, or metabolic syndrome.
Fibrinogen
Fibrinogen is a clotting factor and acute phase inflammatory protein. Elevated fibrinogen above 3.0 g/L is associated with a prothrombotic and pro-inflammatory state that can impair placental development.
CATEGORY 5: GENETIC TESTING
Parental Karyotyping
In women with recurrent miscarriage particularly three or more losses parental karyotyping identifies whether either partner carries a chromosomal abnormality (most commonly a balanced translocation) that is being passed on in an unbalanced form to embryos.
This is typically offered through specialist recurrent miscarriage clinics and is a standard component of investigation after three losses.
Products of Conception Testing
Where possible, testing the chromosomal makeup of miscarried tissue (products of conception) provides direct information about whether the specific loss was chromosomally abnormal. This helps distinguish between random chromosomal error and a recurrent underlying cause.
If you have a miscarriage in hospital or at home where tissue is available, you can request that it be sent for chromosomal analysis. This is not always offered routinely you may need to ask.
HOW TO REQUEST A COMPREHENSIVE INVESTIGATION
Here is exactly what to say to your doctor:
"I would like a comprehensive miscarriage investigation. I understand that the standard panel covers antiphospholipid antibodies and karyotyping, but I would like to also request thyroid function including antibodies, a full thrombophilia screen, fasting insulin and homocysteine, active B12, serum folate, vitamin D, ferritin, hsCRP, prolactin, and Day 21 progesterone.
I have read that many of these markers are independently associated with recurrent pregnancy loss and are modifiable with targeted treatment. I would like the opportunity to investigate them before my next pregnancy."
Not every doctor will order every marker on this list. Some may require specialist referral. But knowing what to ask for is the first step and many of these tests are straightforward to obtain through a GP with a clearly articulated reason.
THE LAB INTERPRETATION GUIDE
Many of the markers covered in this post are explained in full in the Lab Interpretation Guide for Fertility Health including the evidence-based optimal ranges, what each result means, and specific next steps for every result pattern.
It is the resource I give every patient before we begin their miscarriage investigation so they arrive at their appointments informed, specific, and ready to advocate for themselves.
→ Get the Lab Interpretation Guide here $47
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A FINAL WORD
A comprehensive miscarriage investigation is not aggressive medicine. It is not unnecessary testing.
It is the minimum you deserve after the loss of a pregnancy.
Every marker on this list has a reason to be there. Every one of them is connected to a known mechanism of pregnancy loss. And every one of them, if found to be outside the optimal range, has a treatment pathway.
You are not asking for too much.
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