Products of Conception: Understanding Your Pathology Report

Section Editor: Kianoosh Keyhanian MD FRCPC
August 31, 2026

Products of conception is the clinical term for the tissue that forms during a pregnancy. It includes the placenta, the membranes, and, depending on how far the pregnancy had developed, the embryo or fetus. Pathology reports and requisition forms use the phrase, and it can read as cold and technical. It is simply the standard laboratory term for pregnancy tissue.

Most people reading this article have had a pregnancy loss, or have had a procedure after one. If that is your situation, one thing is worth saying at the outset. The great majority of early pregnancy losses happen because of a chromosome error that occurred by chance when the pregnancy formed. They are not caused by working, exercising, lifting, stress, travel, or anything else you did or did not do.

This article explains why this tissue is examined, what the report is likely to say, and what the various findings mean.

Why are products of conception examined?

Pregnancy tissue is sent to a pathologist after a miscarriage, after a procedure to empty the uterus such as a dilation and curettage, or after a termination of pregnancy. The examination answers a few specific questions.

Was the pregnancy inside the uterus? — Finding placental tissue in the specimen confirms that the pregnancy was in the uterus. This is the single most important question the examination answers, because it bears on whether an ectopic pregnancy needs to be considered.
Was there a molar pregnancy? — A molar pregnancy is an uncommon abnormality of the placental tissue that requires specific follow-up. It is often not suspected beforehand, and it is usually found only when the tissue is examined.
Is any tissue left behind? — Retained pregnancy tissue can cause ongoing bleeding or infection, and the findings help guide whether further treatment is needed.
Is there any other explanation? — Occasionally the examination shows something else, such as signs of infection, that helps explain what happened.

What do products of conception look like under the microscope?

Products of conception consist of placental tissue, membranes, and the lining of the uterus, sometimes together with embryonic or fetal tissue. Under the microscope, the pathologist looks for the following.

Chorionic villi — Small, branching, finger-like structures that make up the placenta and carry blood vessels to the developing pregnancy. Finding chorionic villi is what confirms that pregnancy tissue is present.
Trophoblast — The cells that form the outer layer of the villi and anchor the placenta to the uterus. Their appearance is what distinguishes an ordinary pregnancy from a molar pregnancy.
Decidua — The specially prepared lining of the uterus of pregnancy. Decidua confirms that a pregnancy had begun somewhere, but on its own it does not show that the pregnancy was inside the uterus.
The implantation site — The area where the placenta attached to the wall of the uterus.
Embryonic or fetal tissue — In pregnancies that had developed further, recognizable tissue such as cartilage or early organ tissue may be present. In many early losses, none is found, because the pregnancy stopped developing before those tissues formed.
Signs of infection — Inflammation in the tissue can point to an infection as a cause, which is uncommon but important when present.

What does the pathology report usually say?

Most reports on products of conception are short. Wording varies between laboratories, but common results fall into a few groups.

Chorionic villi identified — Placental tissue was found. This confirms the pregnancy was inside the uterus and effectively rules out an ectopic pregnancy in most circumstances.
Products of conception with no atypical features — Pregnancy tissue was present and looked as expected. No molar pregnancy and nothing unusual was found.
Decidua only, no chorionic villi identified — The lining of the uterus showed changes of pregnancy, but no placental tissue was found. This result needs follow-up and is explained in the next section.
Hydropic villi or hydropic change — The villi were swollen with fluid. This is common in a pregnancy that stopped developing and is usually not molar, though it may prompt additional testing to be sure.
Complete or partial hydatidiform mole — A molar pregnancy was found. This is described below.

What does it mean if no chorionic villi were found?

This result matters most urgently, so it is worth understanding clearly. If no placental tissue was found in the specimen, the pathologist cannot confirm that the pregnancy was inside the uterus. Reports usually say something like “no chorionic villi identified” and add that an ectopic pregnancy cannot be excluded.

An ectopic pregnancy implants outside the uterus, almost always in a fallopian tube. It cannot continue, and it can cause serious internal bleeding if it is not treated. This is why the result is followed up promptly rather than waited on.

An absent result does not mean you have an ectopic pregnancy. Other explanations include a very early pregnancy that passed before the procedure, or placental tissue that was present but not captured in the sample. Your doctor will usually order blood tests measuring the pregnancy hormone hCG, repeated over several days, and often a further ultrasound. A falling hCG level is reassuring. A level that stays the same or rises prompts further investigation.

If you have been told that no chorionic villi were found, make sure you know what the follow-up plan is before you leave. Sudden severe abdominal pain, shoulder tip pain, dizziness, or fainting should be treated as an emergency.

What is a molar pregnancy?

A molar pregnancy, also called a hydatidiform mole, happens when an error at fertilization causes the placental tissue to grow abnormally. The villi become swollen and fluid-filled, and the trophoblast cells multiply more than they should. It occurs in roughly 1 in 1,000 pregnancies and is usually diagnosed only after the tissue is examined.

Complete mole — No embryo develops, and all the genetic material comes from the father. All villi show abnormal changes.
Partial mole — An extra set of chromosomes is present, usually because two sperm fertilized one egg. Some normal villi are present alongside the abnormal ones, and there may be embryonic tissue.

Distinguishing the two, and separating them from an ordinary pregnancy loss with swollen villi, can be difficult under the microscope alone. Pathologists often use an additional stain called p57 and sometimes genetic testing to settle the question.

A molar pregnancy is not cancer, but a small proportion continue to grow after the uterus has been emptied, a condition called gestational trophoblastic neoplasia. This is why everyone with a molar pregnancy has their hCG level monitored until it falls to zero and stays there. The risk is roughly 15 to 20 percent after a complete mole and under 5 percent after a partial mole. When treatment is needed, it is usually chemotherapy, and cure rates are very high. Your team will advise you to avoid becoming pregnant again until monitoring is finished, because a new pregnancy would raise hCG and make the results impossible to interpret.

Does the report explain why the pregnancy was lost?

Usually not, and it is worth knowing in advance so the report doesn’t come as a disappointment. Routine examination of products of conception confirms what tissue was present and rules out a molar pregnancy. It is not designed to find the cause of a loss, and in most cases no cause is identified.

The most common cause of early pregnancy loss is a chromosome error that arose by chance as the pregnancy formed. About half of first-trimester losses are due to this, and the proportion is higher in the earliest losses. These errors are random events. They are not inherited, they are not caused by anything either parent did, and they usually do not happen again.

A standard microscope exam cannot detect chromosome errors. That requires separate genetic testing of the tissue, such as a chromosome analysis or a microarray. This has to be requested specifically, and it often needs the tissue to be handled differently at the time of the procedure. If you want that testing, ask about it before a procedure rather than afterward.

What happens next?

What follows depends on the findings and on your situation. Points your doctor may raise include:

Follow-up for an unclear result — If no placental tissue was found, hCG blood tests and sometimes a repeat ultrasound follow-up, as described above.
Monitoring after a molar pregnancy — Regular hCG measurements until the level is undetectable and has stayed that way for a defined period.
Bleeding and recovery — Some bleeding after a procedure is expected. Report heavy bleeding, fever, or foul-smelling discharge promptly, as these can indicate retained tissue or infection.
Rh blood group — If your blood type is Rh negative, you may need an injection of anti-D after a pregnancy loss or procedure. This is decided clinically and is not addressed in the pathology report.
Trying again — Most people who have one miscarriage go on to have a successful pregnancy. Your doctor can advise on timing.
Repeated losses — Investigation is usually offered after two or three losses, and can include genetic testing, hormone and clotting tests, and imaging of the uterus. A single loss usually does not trigger this workup, which reflects how common and random single losses are.

Grief after a pregnancy loss is common at any stage, including very early ones, and it does not require anyone’s permission. If you are struggling, your doctor can point you toward counseling and support services.

Questions to ask your doctor

Were chorionic villi found in the specimen?
Does the report confirm the pregnancy was inside the uterus?
If no villi were found, what is the follow-up plan, and when will I be seen again?
Was a molar pregnancy found or ruled out?
Was any additional testing, such as the p57 stain or genetic testing, performed?
Was all the tissue removed, or could some remain?
Was there any sign of infection?
Does the report say anything about why the pregnancy was lost?
Can the tissue still be sent for genetic testing, or was that opportunity missed?
Do I need anti-D because of my blood type?
How long should I expect bleeding to last, and what would be too much?
When would it be reasonable to try again?
At what point would you investigate further for a cause?
Can you tell me what happens to the tissue after it is examined?