Definition of Placentomegaly
Placentomegaly is defined as a placental thickness exceeding 4 cm on ultrasound, though some sources use a threshold of 6 cm in the third trimester. 1
Measurement Criteria
The definition of placentomegaly varies in the literature based on several factors:
- Most commonly accepted threshold: Placental thickness >4 cm is considered pathologic across gestational ages 1
- Alternative third-trimester threshold: Some studies define placentomegaly as thickness ≥6 cm specifically in the third trimester 1
- Variable factors affecting measurement: The criteria differ based on gestational age, placental location, measurement technique, and maternal or fetal factors 1
Clinical Context
Placentomegaly is easily identified on routine prenatal ultrasound and serves as an important marker for underlying maternal and fetal pathology. 1
Key Assessment Points:
- Routine ultrasound evaluation of placental thickness should be standard practice in prenatal care 1
- Early identification allows for investigation of underlying etiologies and appropriate surveillance 1
- The finding warrants thorough investigation rather than being dismissed as an incidental finding 1
Associated Conditions
Placentomegaly can indicate various maternal and fetal pathologies:
Maternal conditions associated with placentomegaly include obesity, multiparity, anemia, diabetes, preeclampsia, cardiac dysfunction, and infection 1
Fetal conditions include multiple pregnancy, sacrococcygeal teratomas 1, 2, Beckwith-Wiedemann syndrome 1, 3, 4, 5, and placental mesenchymal dysplasia 3, 4, 5
Assisted reproductive technology is also associated with increased placental thickness 1
Clinical Significance
- Increased adverse outcomes: Placentomegaly is associated with higher incidence of adverse pregnancy outcomes and neonatal morbidity and mortality 1
- Surveillance recommendations: While no formal guidelines exist, serial ultrasounds and weekly antenatal testing in the third trimester should be considered when placentomegaly is identified 1
Important Distinction
Do not confuse placentomegaly with placenta accreta spectrum disorders, which involve abnormal trophoblast invasion into the myometrium rather than simple placental enlargement 6