Why Placentas Should Be Sent Without Formalin
Placentas must not be placed in formalin before tissue biopsy is taken because formalin fixation destroys the viability of cells needed for cytogenetic testing (karyotyping, microarray analysis, and QF-PCR), which is essential for identifying chromosomal abnormalities in stillbirth investigations. 1
The Critical Reason: Preserving Tissue for Genetic Testing
When investigating stillbirths and late intrauterine fetal deaths, cytogenetic analysis detects chromosomal abnormalities in 6-13% of cases 1. These genetic tests require living cells that can be cultured in the laboratory. Formalin is a fixative that:
- Cross-links proteins and preserves tissue architecture for histological examination
- Kills all cells, making them unsuitable for cell culture
- Prevents DNA extraction needed for karyotyping and chromosomal microarray
The Correct Specimen Collection Protocol
According to current guidelines 1:
- Take a 1 cm diameter placental biopsy from the fetal surface close to the cord insertion (avoiding maternal tissue)
- Take a 0.5 cm cord biopsy if needed
- Place specimens immediately in sterile tissue culture medium (lactated Ringer's solution or similar transport media)
- Only after genetic samples are secured should the remaining placenta be placed in formalin for histopathological examination
The Workflow Algorithm
- Fresh placenta arrives → First priority: obtain tissue for cytogenetics
- Take biopsies → Place in sterile culture medium (NOT formalin)
- Send for genetic testing → Karyotype, microarray, QF-PCR as indicated
- Then fix remaining placenta → Place in formalin for routine histopathology
Common Pitfall to Avoid
The most critical error is placing the entire placenta in formalin upon receipt, which permanently eliminates the possibility of cytogenetic testing. This mistake cannot be reversed and may deprive families of crucial information about:
- Recurrence risk in future pregnancies
- Cause of fetal death
- Need for genetic counseling
What About Formalin's Effect on Weight?
While research shows formalin fixation increases placental weight by approximately 3.7-7.67% 2, 3, this is a separate consideration for pathological assessment and does not change the primary directive: genetic samples must be obtained before any formalin exposure.
Additional Context on Placental Pathology Importance
Placental examination is the single most useful investigation in stillbirth evaluation, identifying probable cause of death in 11.2-64.9% of cases 1. However, this histopathological examination (which requires formalin fixation) must occur after viable tissue is secured for genetics.