PGT-A Mosaicism to CPM

PGT-A Mosaicism to CPM and Pregnancy Phenotype

PGT-A Result	Approx. Mosaic Level	Likelihood of CPM	Placental Phenotype	Typical Pregnancy Phenotype	Key Clinical Implications
Euploid	0%	Very low	Normal placental development	Normal growth, low risk	Standard antenatal care unless other risk factors
Low-level mosaic	~20–30%	Low–moderate	Usually compensated placenta	Often normal pregnancy; occasional late FGR	Do not over-reassure; baseline third-trimester growth scan
Low–intermediate mosaic	~30–40%	Moderate	Patchy placental mosaicism	Mild or late-onset FGR possible	Serial growth surveillance recommended
Intermediate mosaic	~40–50%	Moderate–high	Reduced placental reserve	Growth deceleration, abnormal uterine Dopplers	Treat as placenta-driven; Doppler surveillance
High-level mosaic	~50–70%	High	Functionally compromised placenta	Early-onset FGR, preeclampsia, IUFD risk	High-risk surveillance irrespective of fetal karyotype
Very high mosaic / near-aneuploid	>70%	Very high	Severe placental dysfunction	Implantation failure, early loss, severe FGR	Counsel for high obstetric risk if ongoing pregnancy
Segmental mosaicism	Any %	Variable (chromosome-dependent)	Localized placental defects	Variable growth restriction or focal placental pathology	Interpret by chromosome and size of segment

Modifiers That Shift Risk Up or Down

Chromosome Involved

• High CPM-risk chromosomes (16, 22, 15): shift risk one tier higher
• Intermediate (7, 8, 12, 20): risk as listed
• Low CPM-risk (21, 18, 13): shift risk one tier lower if growth normal

CPM Type (If Known)

• Type 3 (mitotic, placental lineage): highest placental risk
• Type 2: mixed placental–fetal risk
• Type 1: lowest placental impact

Clinical Course Overrides Genetics

• Falling growth centiles, abnormal Dopplers, or preeclampsia → treat as high-risk placenta, regardless of PGT-A level

Identify the Chromosome Involved

(From NIPT, CVS, placental biopsy, or suspected CPM based on phenotype)

• A. Chromosomes with High Placental Vulnerability - 16, 22, 15, 9, 2
• B. Chromosomes with Intermediate Placental Impact - 7, 8, 12, 20
• C. Chromosomes with Predominantly Fetal Risk - 21, 18, 13
• D. Sex Chromosomes - 45,X mosaic, X mosaicism, Y

Red Flags

• Early-onset FGR (<28 weeks)
• Progressive drop in growth centiles
• Abnormal uterine or umbilical Dopplers
• Oligohydramnios
• Maternal preeclampsia
• Unexplained abnormal uterine artery Dopplers
• Disproportionate placental thickness, cysts, or infarcts
• Recurrent placental pathology in prior pregnancies

Key Points

• “A normal amniocentesis does not exclude placental disease.”
• “The chromosome involved tells us how closely we need to watch the placenta.”
• “Growth and Dopplers matter more than anatomy once CPM risk is suspected.”

Where it Fits Best

• NIPT–amnio discordance
• CVS mosaicism
• Early, unexplained FGR
• Prior pregnancy with placental insufficiency

Prenatal Testing Discordance

• High-risk NIPT with normal amniocentesis
• Mosaic or abnormal CVS followed by normal fetal karyotype

Clinical Signs That Increase Suspicion of CPM

Ultrasound and Doppler Indicators

• Persistent uterine artery notching or high PI
• Umbilical artery PI at upper normal range early in gestation
• Asymmetric FGR with relatively preserved anatomy
• Progressive fall across growth centiles rather than static small size

Placental Morphology Clues

• Thickened placenta with heterogeneous echotexture
• Placental lakes, cysts, or focal echogenic areas
• Marginal or velamentous cord insertion

Counseling Anchors

• “PGT-A reflects placental genetics, not fetal destiny.”
• “A normal fetus can still be affected by an abnormal placenta.”
• T16 CPM - High-risk, placenta-driven pathway even with a normal fetus
• T7 / SRS-type cases - Moderate zone
• Discordant NIPT (T22) – NO false reassurance after a normal amnio
• Low-risk mosaics stay low risk, which protects against unnecessary surveillance