Placentomegaly — Causes
Definition:
Placentomegaly refers to an abnormally thick or enlarged placenta, typically defined as:
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>4 cm thick at 20 weeks gestation, or
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>6 cm thick at term.
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| plaenta normal anterior image |
I. Maternal Causes
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Diabetes mellitus (especially poorly controlled)
→ due to villous edema and increased fetal size. -
Maternal anemia (especially severe)
→ compensatory placental hypertrophy to improve oxygen transfer. -
Maternal infection
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TORCH infections (Toxoplasmosis, Rubella, CMV, Herpes)
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Syphilis, Malaria, Hepatitis, HIV
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Hypertension with superimposed infection or diabetes
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Rh isoimmunization (leading to fetal hydrops and placental edema)
II. Fetal Causes
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Fetal hydrops (immune or non-immune)
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Most common fetal cause.
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Due to excessive fluid accumulation → placental edema.
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Chromosomal abnormalities
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Trisomy 13, 18, 21, Triploidy, Turner syndrome
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Fetal anemia (any cause, e.g., parvovirus B19 infection)
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Twin-to-twin transfusion syndrome (recipient twin side)
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Large-for-gestational-age (LGA) fetus
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Often secondary to maternal diabetes.
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| a large placenta |
III. Placental / Cord Causes
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Chorioangioma (benign vascular tumor of placenta)
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Molar pregnancy (partial mole)
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Chronic villitis or placentitis
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Placental edema due to venous obstruction (cord anomalies)
IV. Other / Miscellaneous Causes
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Congenital infections (CMV, syphilis, toxoplasmosis, parvovirus)
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Placental transfusion syndromes
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Maternal-fetal hemorrhage
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High altitude pregnancies (chronic hypoxia)
Mnemonic (for quick recall):
“BIG PLACENTA”
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B – Beta-thalassemia / fetal anemia
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I – Infections (TORCH, malaria, syphilis)
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G – Gestational diabetes
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P – Parvovirus / Polyhydramnios
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L – Large baby (LGA)
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A – Aneuploidy (Trisomy 13/18/21)
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C – Chorioangioma
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E – Erythroblastosis fetalis (Rh isoimmunization)
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N – Nonimmune hydrops
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T – Twin-to-twin transfusion
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A – Anemia (maternal or fetal)
- An enlarged placenta isn’t usually a reason to panic. The word is big (placentomegaly), but most of the time it doesn’t cause problems.
- Some conditions play a role. A larger placenta may be linked to hypertension, anemia, or diabetes — but your doctor will monitor these and the health of your baby.
- Your baby’s growth matters most. Even if your placenta measures big, steady fetal development is the important goal, so keep up your regular appointments to be sure everything’s right on track.
