What Does 'p57 Staining' Mean on My Pathology Report?

Reading a pathology report after a pregnancy loss can be overwhelming, especially when it is filled with unfamiliar medical terms. p57 immunohistochemical staining is a specific laboratory test pathologists use on miscarriage tissue to help determine if you had a molar pregnancy. Because the p57 protein is normally only produced by maternal genes, finding it in the pregnancy tissue indicates that a maternal genomic contribution is present. This makes a typical complete molar pregnancy very unlikely, helping your care team determine the right follow-up care for you.

What is p57?

To understand p57, it helps to know a little about genetics. We inherit one set of chromosomes from our mother and one set from our father. For most genes, both copies are active. However, a small number of genes are “imprinted,” meaning only the copy from one specific parent is turned on ^[1].

The gene that produces the p57 protein (officially called CDKN1C) is one of these special genes. It is only active (expressed) when it comes from the mother; the copy from the father is naturally silenced ^[1]. Because of this unique trait, pathologists use p57 as a marker to see if maternal DNA is active in the specific placental cells (villous cells). Pathologists also look at your own maternal cells in the sample (such as the decidua) as an “internal control” to make sure the stain worked properly ^[2].

How the Test Works and What the Results Mean

When a pathologist examines tissue after a miscarriage, they apply a chemical stain that reacts to the p57 protein.

• Negative p57 (Absent staining): If the placental cells do not show the stain (while the control cells do), it means the p57 protein is missing. This indicates that no active maternal chromosome set is present in those cells ^[2]. This is the hallmark of a complete molar pregnancy, a condition where the genetic material comes only from the father ^[3].
• Positive p57 (Present or Retained staining): If the placental cells show the stain, it means maternal genetic material is present ^[1]. This result strongly argues against a typical complete molar pregnancy ^[3]. However, a positive p57 stain is seen in both partial molar pregnancies and typical (non-molar) miscarriages ^[4]. It is important to know that p57 is not a stand-alone diagnosis and must always be interpreted alongside other findings ^[5].

Beyond p57: Triploidy and Genetic Testing

Because a positive p57 result can mean either a partial mole or a standard miscarriage, the pathologist cannot rely on the stain alone ^[4]. They will also look closely at the microscopic pattern of the tissue. In many cases, they will recommend additional genetic tests:

• Ploidy analysis: This tests the total number of chromosomes. While most pregnancies have 46 chromosomes, a triploid pregnancy has 69 (three sets instead of two) ^[6].
• Genotyping: This looks at specific DNA markers to determine where the extra chromosomes came from ^[7]. If the extra set is from the father (diandric triploidy), it supports a diagnosis of a partial molar pregnancy ^[8]. If the extra set is from the mother (digynic triploidy), it is generally a non-molar miscarriage ^[6].

Please know that triploidy and molar pregnancies are sporadic genetic events. They are not caused by anything you did or didn’t do.

Why This Matters for Your Care

Molar pregnancies carry a risk of a complication called Gestational Trophoblastic Neoplasia (GTN), where abnormal tissue persists or becomes active after the pregnancy ends ^[8]. Complete moles carry a higher risk for this than partial moles.

If your final diagnosis is a partial molar pregnancy, your care team will monitor your health using serial blood tests to track your pregnancy hormone (hCG) ^[8]. These tests ensure your hCG levels consistently fall to an undetectable, normal range. Because a new pregnancy would cause your hCG to rise and make surveillance difficult, your doctor will advise you to use reliable contraception and avoid pregnancy until your monitoring is officially complete.

Note: If you experience heavy or worsening vaginal bleeding, severe abdominal pain, fever, fainting, marked dizziness, or shortness of breath, seek immediate medical attention or go to an emergency room, as these can be signs of urgent complications.