Medically reviewed by Dr. Pamela Frank, BSc(Hons), ND
If you’ve been reading about thyroid, PCOS, or endometriosis on this site and are now wondering whether any of them could be connected to a miscarriage, you’re asking a reasonable question. All three conditions have documented links to pregnancy loss, and all three are areas I regularly test and address.
A note on scope: this page focuses specifically on the thyroid, PCOS/insulin resistance, and endometriosis connections to miscarriage risk. If you’ve experienced two or more pregnancy losses, a much broader workup is warranted, covering genetic, anatomical, and immunological factors well beyond what’s discussed here. For that comprehensive breakdown, see the full recurrent pregnancy loss guide on fertilityhelp.ca →
How Thyroid Dysfunction Connects to Miscarriage Risk
Both overt and subclinical hypothyroidism are associated with increased miscarriage risk. A 2017 systematic review and meta-analysis found that women with untreated subclinical hypothyroidism (an elevated TSH with normal free T4) had close to double the rate of miscarriage compared to euthyroid (normal thyroid) women, and that risk rose further, to nearly two and a half times, when thyroid autoimmunity was also present.1 This matters because subclinical hypothyroidism is often missed. Standard lab reference ranges for TSH are wider than what’s appropriate during conception and early pregnancy, where a target below 2.5 mIU/L is generally used rather than the standard upper limit of 4.0–5.0 mIU/L.2
Thyroid autoimmunity deserves separate attention from TSH itself. Anti-thyroid antibodies (anti-TPO and anti-thyroglobulin) are associated with elevated miscarriage risk even when TSH and thyroid hormone levels are entirely normal, a pattern seen across multiple meta-analyses.3 This is one of the more commonly overlooked findings in a standard prenatal workup, since thyroid antibody testing is rarely ordered when TSH looks fine.
For more on thyroid testing and treatment, see the hypothyroidism page →
How PCOS and Insulin Resistance Connect to Miscarriage Risk
Women with PCOS have long been observed to have higher miscarriage rates than the general population, and insulin resistance is one of the more consistently proposed mechanisms, through effects on oocyte quality, endometrial receptivity, and hormonal signalling during early pregnancy. Insulin resistance can also be present in women without a formal PCOS diagnosis (a diagnosis that is often missed!), including those who have lean PCOS, and contributes through overlapping mechanisms.
It’s worth being direct about the state of the evidence here: a 2023 review of the literature on PCOS and recurrent pregnancy loss concluded that, while an association is well established, the studies investigating exactly which PCOS-related factors (insulin resistance, elevated androgens, BMI, inflammatory markers, among others) drive that risk are still limited and inconsistent, and the authors called for further research rather than treating the mechanism as settled.4 A separate, larger meta-analysis of PCOS pregnancy outcomes confirms the elevated risk itself is real, even as the precise mechanism continues to be studied.5
What this means practically: if you have PCOS and are also dealing with miscarriage or pregnancy loss, insulin resistance is a reasonable and modifiable factor to investigate, but it’s unlikely to be the whole picture, and a broader assessment is worthwhile.
For more on PCOS testing, phenotypes, and treatment, see the PCOS page →
How Endometriosis Connects to Miscarriage Risk
Endometriosis has a well-documented association with pregnancy loss. A 2020 systematic review and meta-analysis of nearly 700,000 women found that endometriosis was associated with roughly 80% higher odds of miscarriage in spontaneously conceived pregnancies compared to women without the condition, though this elevated risk was not seen in pregnancies conceived through assisted reproductive technology in the same analysis.6
The proposed mechanisms are still an active area of research, but the leading explanations involve chronic pelvic inflammation and progesterone resistance, meaning the endometrial lining doesn’t respond normally to progesterone’s signal to prepare for and sustain implantation, even when circulating progesterone levels are adequate. This is a distinct mechanism from the luteal phase insufficiency discussed below, where the issue is progesterone production rather than the tissue’s response to it.
For more on endometriosis testing and treatment, see the endometriosis page →
Where This Overlaps With General Hormone Imbalance
Both thyroid dysfunction and insulin resistance can contribute to luteal phase insufficiency, low progesterone in the second half of the cycle, which is itself directly relevant to early pregnancy maintenance. If you’re dealing with irregular cycles, PMS, or other signs of hormone imbalance alongside pregnancy loss, these threads are often connected rather than separate issues. See the hormone imbalance page → for a broader picture.
What Miscarriage Testing Looks Like
For thyroid and metabolic contributors specifically, the testing I typically recommend includes:
- Full thyroid panel, including TSH, free T4, free T3, reverse T3, and both anti-TPO and anti-thyroglobulin antibodies (not TSH alone)
- Fasting insulin, glucose and HOMA-IR, to assess insulin resistance even if fasting glucose is normal
- Day 21 progesterone, to assess luteal phase adequacy
- Day 3 LH, FSH, estradiol, to assess follicular development
- Total and free testosterone, DHEAs, androstenedione, dihydrotestosterone, to assess PCOS
- 7-9 a.m. cortisol, to gauge adrenal gland function and stress
- CRP, to assess general inflammation levels
This is a general overview of testing that may be relevant for miscarriage. Each case is unique, and so is appropriate testing.
See the lab testing page → for more on how testing works.
If You’ve Had Two or More Losses
Current guidelines from the European Society of Human Reproduction and Embryology recommend a full investigation after two consecutive pregnancy losses rather than waiting for three.1 If that’s where you are, thyroid and PCOS-related factors are worth investigating, but they’re only part of a much larger picture that includes genetic, anatomical, and immunological causes. The comprehensive recurrent pregnancy loss guide on fertilityhelp.ca → walks through the full workup and treatment protocol in detail.
Working With a Naturopathic Doctor
Investigating the hormonal and metabolic contributors to miscarriage risk works alongside, not instead of, your family doctor, fertility clinic or OB/gyne. I can order thyroid antibody panels, fasting insulin, and all other relevant testing listed above, and coordinate care where a finding needs medical follow-up.
All of these issues can be improved significantly through naturopathic treatment for PCOS, thyroid, and endometriosis.
See what to expect from the naturopathic process → or book an appointment →.
Frequently Asked Questions About Miscarriage
Can thyroid problems cause miscarriage even if my TSH is normal?
Yes, this is possible. Thyroid antibodies (anti-TPO and anti-thyroglobulin) are associated with elevated miscarriage risk independently of TSH and thyroid hormone (free T3 and free T4) levels, which is why antibody testing matters even when standard thyroid results look normal.
Does having PCOS mean I’m more likely to miscarry?
Studies do show higher miscarriage rates in women with PCOS, though the research on exactly which PCOS-related factors drive that risk is still developing. Insulin resistance is one of the more consistently investigated contributors.
Does endometriosis increase my risk of miscarriage?
Research suggests it does, particularly in spontaneously conceived pregnancies. The proposed mechanisms involve chronic pelvic inflammation and progesterone resistance in the endometrial lining, though this remains an active area of research.
Is this the same as a recurrent pregnancy loss workup?
No. This page covers thyroid, endometriosis and PCOS/insulin resistance specifically. A full recurrent pregnancy loss workup, appropriate after two or more losses, also investigates genetic, anatomical, and immunological factors. See the comprehensive guide linked above.
Should I get tested even after just one miscarriage?
Guidelines generally reserve full recurrent pregnancy loss investigation for two or more losses. That said, if you have known thyroid or PCOS-related symptoms, testing thyroid antibodies or fasting insulin and androgens proactively as part of general hormone health is reasonable to discuss with your practitioner.
Thyroid, PCOS, Endometriosis and Miscarriage References
- Zhang Y, Wang H, Pan X, Teng W, Shan Z. Patients with subclinical hypothyroidism before 20 weeks of pregnancy have a higher risk of miscarriage: A systematic review and meta-analysis. PLoS One. 2017 Apr 17;12(4):e0175708. doi: 10.1371/journal.pone.0175708. PMID: 28414788; PMCID: PMC5393567.
- Casey BM, Dashe JS, Wells CE, McIntire DD, Byrd W, Leveno KJ, Cunningham FG. Subclinical hypothyroidism and pregnancy outcomes. Obstet Gynecol. 2005 Feb;105(2):239-45. doi: 10.1097/01.AOG.0000152345.99421.22. PMID: 15684146.
- Thangaratinam S, Tan A, Knox E, Kilby MD, Franklyn J, Coomarasamy A. Association between thyroid autoantibodies and miscarriage and preterm birth: meta-analysis of evidence. BMJ. 2011 May 9;342:d2616. doi: 10.1136/bmj.d2616. PMID: 21558126; PMCID: PMC3089879.
- Wartena R, Matjila M. Polycystic ovary syndrome and recurrent pregnancy loss, a review of literature. Front Endocrinol (Lausanne). 2023 Oct 30;14:1183060. doi: 10.3389/fendo.2023.1183060. PMID: 38027110; PMCID: PMC10643146.
- Bahri Khomami M, Shorakae S, Hashemi S, Harrison CL, Piltonen TT, Romualdi D, Tay CT, Teede HJ, Vanky E, Mousa A. Systematic review and meta-analysis of pregnancy outcomes in women with polycystic ovary syndrome. Nat Commun. 2024 Jul 4;15(1):5591. doi: 10.1038/s41467-024-49749-1. PMID: 38965226; PMCID: PMC11224312.