Thick Placenta in Pregnancy: A Review

Importance A thickened placenta is easily identified on ultrasound and provides insight into maternal and fetal wellbeing as well as underlying structural and physiologic anomalies. Objectives The aim of this study was to review the literature to clarify what classifies a placenta as “thickened” and to review the associated incidence, maternal and fetal comorbidities, and management during pregnancy. Evidence Acquisition Electronic databases (PubMed and Web of Science) were searched from 2000 to 2020 in the English language. Studies were selected that examined associations between placental thickness, potential etiologies, and obstetric outcomes. Results There were 140 abstracts identified. After reviewing the articles, 60 were used in this review. Routine assessment of the placenta in the prenatal period is an easy and inexpensive way to assess the maternal and fetal patients. The criteria for a “thickened placenta” vary between studies based on gestational age, placental location, measurement technique, and maternal or fetal factors. Whereas most suggest thickness exceeding 4 cm is pathologic, a review had a threshold of 6 cm in the third trimester to classify placentomegaly. Several maternal and fetal conditions have been associated with a thickened placenta, such as obesity, parity, anemia, diabetes, preeclampsia, cardiac dysfunction, infection, assisted reproductive technology, multiple pregnancy, sacrococcygeal teratomas, and Beckwith-Wiedemann syndrome. A thickened placenta in pregnancy is associated with a higher incidence of adverse pregnancy outcomes and neonatal morbidity and mortality. Conclusions The literature is clear that early evaluation of the placenta using ultrasound should be a standard practice. A thickened placenta found on routine imaging should prompt a more thorough investigation to determine the etiology of the placentomegaly. At the time of this literature review, there are no recommendations regarding modality or frequency of antenatal surveillance in pregnancies complicated by a thickened placenta. However, serial ultrasounds and weekly antenatal testing in the third trimester should be considered. Relevance A thickened placenta has been associated with a variety of maternal and fetal conditions and increases the risk of adverse pregnancy outcomes and neonatal morbidity and mortality. Target Audience Obstetricians, nurse midwives, pediatricians, family physicians Learning Objectives After completion of this article, the reader should be able to classify the diagnostic criteria of thickened placenta in pregnancy; identify associated maternal and fetal conditions in the setting of a thickened placenta; and predict the adverse outcomes of pregnancy related to a thickened placenta.