Miscarriage Tissue Testing: Karyotype or Microarray?
If you are reading this while it is happening, you are likely being told two things at once: that your insurance will not cover tissue testing after this loss, and that you have to decide, quickly, between two tests you have never heard of. Karyotype and chromosomal microarray both try to answer the same question — was this pregnancy chromosomally normal — but they get it wrong in different ways, and which one fails you least depends on your specific situation. This is written to help you choose, not to tell you what to choose.
My miscarriage tissue can be tested — should I pay for karyotype or microarray?
If a previous sample failed to grow, or the tissue will not reach a lab fresh, chromosomal microarray (CMA, sometimes called a SNP array) is the more reliable choice because it works on DNA rather than living cells and does not depend on culture. If you are certain the tissue will be collected fresh, kept in saline, and sent to a lab the same day, karyotype remains a reasonable, usually less expensive option, though it carries its own risk of a misleading "normal" result from maternal cell contamination. Where possible, ask the lab whether they offer both on the same sample.
What is a karyotype test on pregnancy tissue, and why does it sometimes fail?
A traditional karyotype requires living cells from the products of conception to divide in a culture dish until they reach metaphase, the point in cell division when chromosomes condense enough to be counted and photographed under a microscope. That requirement is the test's central weakness: the cells have to still be alive and capable of dividing when they arrive at the lab. Tissue that has been sitting for hours, tissue that has partially degraded after passing at home, or tissue that was fixed in formalin instead of kept fresh often will not grow at all. When culture fails, the lab has no result to report, and you are left having paid for a test that answered nothing. Turnaround is also slower than most people expect — culturing to metaphase and analyzing the result typically takes one to three weeks, not days.
This is not a rare glitch. In a prospective study that sent chorionic villi from the same first-trimester miscarriage sample to three different labs for standard cytogenetics, SNP microarray, and array comparative genomic hybridization, growth failure occurred in the cytogenetics arm on samples that were still successfully analyzed by the molecular platforms — and three of those four failed cultures turned out to be chromosomally abnormal by microarray. In other words, culture failure does not fail at random; it can quietly erase exactly the abnormal results a couple most needs to see.
What is chromosomal microarray, and how is it different from a karyotype?
Chromosomal microarray analyzes DNA directly, comparing thousands to millions of genetic markers against a reference genome, without needing any cell to divide. Because it does not depend on culture, it can work on tissue that a karyotype cannot use: tissue that has partially degraded, tissue that arrived a day or two late, and — with the right lab protocol — tissue that was fixed rather than kept fresh, though fresh tissue in saline still gives every platform the best chance of a usable result. Microarray also resolves more detail than a standard karyotype. A karyotype detects whole extra or missing chromosomes and large structural rearrangements visible under a microscope; microarray additionally detects submicroscopic deletions and duplications — copy-number changes too small for a microscope to resolve at all.
The specific type of microarray matters. A SNP-based array (single-nucleotide polymorphism array) can distinguish the mother's DNA from the pregnancy's DNA and can identify triploidy — a full extra set of chromosomes, one of the more common causes of early loss. An older-style oligonucleotide (oligo) array, which measures DNA copy number without SNP information, may miss triploidy entirely because a triploid sample still shows a normal copy-number ratio at most positions. If your lab offers microarray, it is worth asking specifically whether it is a SNP array.
What is maternal cell contamination, and why can a "normal" karyotype be wrong?
Maternal cell contamination happens when the tissue that grows in culture, or gets analyzed, is actually the mother's own cells rather than the pregnancy's — from surrounding decidua, blood, or other maternal tissue mixed into the sample. Because the mother is chromosomally normal (46,XX), a contaminated sample reports back as a normal female karyotype even when the pregnancy itself was abnormal. This is one of the most consequential blind spots in miscarriage tissue testing, because a "46,XX, normal" result is exactly the result that sends a couple down the expensive, often fruitless path of immune and clotting workups when the real answer was a chromosomal one all along.
The scale of this problem has been measured directly. A review of 1,222 first-trimester miscarriage specimens sent for chromosome testing found 630 results reported as normal 46,XX or 46,XY; of the 46,XX results, 269 were maternal cell contamination with no embryonic component detected at all. Once those contaminated samples were excluded, the true chromosomal abnormality rate in the cohort rose from 48 percent to 62 percent. SNP-based microarray can flag this directly by comparing fetal and maternal genetic markers within the same sample, something a standard karyotype has no built-in way to do.
What does chromosomal microarray miss that a karyotype can catch?
Microarray is not a strictly better test in every dimension — it has its own blind spot. It cannot detect balanced chromosomal rearrangements: translocations or inversions where the total amount of genetic material is normal but rearranged, because there is no net gain or loss of DNA for the array to measure. A karyotype, which visually inspects chromosome structure, can catch a balanced rearrangement that microarray would report as normal. Balanced rearrangements are uncommon findings on parental testing, but they are not vanishingly rare — a 16-year cross-sectional study of 4,030 individuals from 2,015 couples with recurrent pregnancy loss found chromosomal abnormalities in 3.3 percent of cases, and 97.7 percent of those were structural rearrangements rather than numeric ones. That statistic applies to parental blood karyotype, not tissue testing, but it explains why parental karyotype stays on the table as a separate test even after tissue microarray comes back normal, particularly after a second or third loss.
A large single-laboratory series that ran SNP microarray on 2,392 products-of-conception specimens under 20 weeks of gestation obtained a usable result in 99.9 percent of cases, identified maternal cell contamination in 22 percent of specimens, and — among the samples confirmed to be of true fetal origin — found submicroscopic chromosomal imbalances in a meaningful share of the specimens that looked normal at the standard cytogenetic resolution. That combination — near-universal success, contamination detection, and finer resolution — is the practical case for choosing microarray when you can only afford one test and the tissue's handling is uncertain.
What should I say to the hospital or clinic before the procedure — saline, not formalin?
This is the single most actionable fact in this decision, and it is easy to get wrong under pressure in an emergency room or during a passage at home. Tissue intended for karyotype must reach the lab fresh, in sterile saline, not formalin — formalin cross-links DNA and kills any dividing cells, so a karyotype culture on formalin-fixed tissue will almost always fail outright. Tissue intended for microarray tolerates more variation, but fresh saline-preserved tissue still gives either platform the best chance of a usable result, so saline is the right default regardless of which test you choose.
If you are having a D&C or D&E, say this to the surgical team beforehand, in writing if you can: "Please send the products of conception fresh, in saline, to cytogenetics for chromosomal microarray — not formalin, not routine pathology only." That sentence prevents the two most common mistakes: the tissue going into a formalin jar by default, and the tissue going only to a pathology lab that examines it visually but never sends it for genetic testing. If you are passing tissue at home, ask your OB-GYN's office in advance what container to use and where to bring the sample, before you are in the middle of the loss. If cost allows only one test and a previous sample failed to grow, tell the lab that plainly and ask for microarray for that reason; if cost allows both, ask whether they offer a reflex pathway that runs microarray automatically when a karyotype culture fails. One more thing worth asking by name: a requisition that reads only "POC testing" or "chromosome analysis" does not tell you which method the lab will actually run, so ask which of the two is being ordered rather than assuming.
Does insurance ever cover this, and roughly what does it cost?
Coverage is inconsistent and often depends on whether you have already had a prior loss, how your clinician codes the test, and your specific plan — there is no reliable rule to give you here, and you should ask your insurer directly with the exact CPT codes your lab intends to bill before you decide. Out of pocket, tissue genetic testing is a real expense, generally in the low hundreds to low thousands of dollars depending on the platform and the lab, and microarray is usually, though not always, the more expensive of the two. This is a cost worth putting in perspective rather than a reason to skip testing altogether: an abnormal result and a normal result are each worth money, because they point your next workup in opposite directions, and paying for an answer that turns out unreadable due to culture failure is the outcome most worth avoiding.
If the result comes back chromosomally abnormal, what does that change?
A confirmed chromosomal abnormality in the pregnancy tissue is, in a narrow and specific sense, useful information: it explains this loss without implicating your uterus, your thyroid, your clotting system, or your immune system, and it usually argues against an immediate, expensive hunt through those systems after a single loss. Most sporadic chromosomal abnormalities in early pregnancy loss are not inherited and do not recur at a meaningfully higher rate in a subsequent pregnancy for most couples. That said, a chromosomally abnormal result does not close every question — if it is a specific structural rearrangement, or if you have had more than one loss, your OB-GYN or reproductive endocrinologist may still recommend parental karyotype to check whether a balanced rearrangement in one parent could be producing this recurrently.
If the result comes back chromosomally normal, what does that mean — and what happens next?
A genuinely chromosomally normal result — confirmed as truly fetal, not maternal contamination — is the result that justifies looking elsewhere: uterine structure and adhesions, thyroid function, glucose and insulin regulation, antiphospholipid antibodies, and parental karyotype if this is a second or later loss. This is not a smaller answer than an abnormal one; it is the answer that tells you and your clinician where to spend the next round of testing instead of guessing. Guidance from the American Society for Reproductive Medicine and from the American College of Obstetricians and Gynecologists both frame a confirmed normal chromosomal result in miscarriage tissue as a reason to evaluate anatomic, endocrine, autoimmune, and thrombophilic factors rather than stop the workup. If you are at that point, the relevant next steps include the kind of uterine and structural evaluation covered in our piece on when laparoscopy is used to investigate recurrent pregnancy loss, the clotting-related testing discussed in what a positive lupus anticoagulant result means while awaiting full antiphospholipid testing, and the immune and thyroid questions raised in how autoimmune issues are actually evaluated after recurrent miscarriage and how thyroid function is checked in a fertility workup.
Is testing every miscarriage's tissue actually the recommended standard?
No, and it is worth saying honestly rather than pretending there is universal agreement. ACOG's practice bulletin on early pregnancy loss discusses genetic evaluation of pregnancy tissue as a reasonable option, particularly for a second or subsequent loss, to help direct further workup, but it does not mandate testing after every single miscarriage. ESHRE's guideline on recurrent pregnancy loss, most recently updated in 2022, takes a more conservative stance and does not universally recommend routine cytogenetic testing of pregnancy tissue, even though the test is widely used in clinical practice across the United States. Both positions are defensible: testing after a first loss mainly offers reassurance and information, while testing after a second or third loss starts to change what gets investigated next. If you are choosing to pay out of pocket during a second loss, as the situation described here, you are already past the point where most guidelines see clear value in the answer — the disagreement in the literature is mostly about whether every single first miscarriage warrants the expense, not about whether the test itself is useful.
What should I do differently if this happens again?
If this is your second loss, ask your OB-GYN or reproductive endocrinologist directly whether the tissue plan should be decided in advance rather than in the moment — many practices in Huntington and elsewhere on Long Island now build a saline-collection instruction into intake paperwork once a patient has had one prior loss, specifically so the decision is not being made from a hospital bed. It is also reasonable to ask what happens with your hCG numbers afterward, since tracking them to zero is its own piece of the picture, covered in our explanation of what to expect with hCG and your period after a miscarriage, and if you pass tissue with medication rather than a procedure, how that changes what can realistically be collected, which we cover in what to expect from misoprostol for miscarriage management. If a clotting or antibody question has already come up for you, it is also worth reading about how a single gene variant is often over-weighted in this workup, in our piece on why MTHFR alone rarely explains recurrent pregnancy loss.
Two miscarriages is the point where most reproductive endocrinologists start a fuller structural, metabolic, and immune workup for recurrent pregnancy loss regardless of what any single tissue result shows, and that broader evaluation is where a metabolic and immune-focused workup earns its keep — not by replacing your OB-GYN's testing, but by organizing glucose and insulin regulation, thyroid and inflammatory markers, and blood flow to the uterus into one coherent picture for whoever manages your care next. Whichever test you choose this time, the tissue itself and the decision about what to test for it are both worth taking seriously, because both a chromosomally normal and a chromosomally abnormal answer change what happens next — the only genuinely wasted outcome is a test that comes back with no result at all.
This article is for general educational purposes and is not a substitute for individualized medical care. Testing, diagnosis, genetic screening and any medication decisions belong with your OB-GYN or reproductive endocrinologist, based on your own history.
East to West Fertility is a systems biology fertility clinic in Huntington, Long Island, serving patients across Long Island, NYC, and beyond. Learn more about our Metabolic & Immune Fertility Evaluation or call 631-416-4940.
Tissue testing is one piece of a larger workup. Our guide to the top tests to ask for after a miscarriage covers what comes next, in what order, and why timing matters.
References:
American College of Obstetricians and Gynecologists' Committee on Practice Bulletins—Gynecology. "ACOG Practice Bulletin No. 200: Early Pregnancy Loss." Obstetrics & Gynecology, 2018;132(5):e197-e207.
Practice Committee of the American Society for Reproductive Medicine. "Evaluation and treatment of recurrent pregnancy loss: a committee opinion." Fertility and Sterility, 2012;98(5):1103-1111.
ESHRE Guideline Group on RPL. "ESHRE guideline: recurrent pregnancy loss." Human Reproduction Open, 2018;2018(2):hoy004.
ESHRE Guideline Group on RPL. "ESHRE guideline: recurrent pregnancy loss: an update in 2022." Human Reproduction Open, 2023;2023(1):hoad002.
Lathi RB, Gustin SL, Keller J, Maisenbacher MK, Sigurjonsson S, Tao R, Demko Z. "Reliability of 46,XX results on miscarriage specimens: a review of 1,222 first-trimester miscarriage specimens." Fertility and Sterility, 2014;101(1):178-182. (1,222 specimens, single reference laboratory.)
Shah MS, Cinnioglu C, Maisenbacher M, Comstock I, Kort J, Lathi RB. "Comparison of cytogenetics and molecular karyotyping for chromosome testing of miscarriage specimens." Fertility and Sterility, 2017;107(4):1028-1033. (Prospective blinded cohort, 60 samples split across three platforms.)
Levy B, Sigurjonsson S, Pettersen B, Maisenbacher MK, Hall MP, Demko Z, Lathi RB, Tao R, Aggarwal V, Rabinowitz M. "Genomic imbalance in products of conception: single-nucleotide polymorphism chromosomal microarray analysis." Obstetrics & Gynecology, 2014;124(2 Pt 1):202-209. (2,392 specimens, single laboratory.)
Aynaci S, Kocagil S, Tosumoglu E, Susam E, Kilic B, Gokalp EE, Cilingir O, Aras BD, Tekin B, Artan S. "Chromosomal abnormalities in couples with recurrent pregnancy loss: a 16-year cross-sectional study of 4030 cases from Turkey." Annals of Saudi Medicine, 2025;45(3). (4,030 individuals, 2,015 couples, single tertiary center.)
