The Association between Disproportionate Birth Weight to Placental Weight Ratio, Clinical Outcome, and Placental Histopathological Lesions.

INTRODUCTION: High and low birth weight (BW) to placental weight (PW) ratios (BW/PW) have been proposed as markers of placental malfunction. We studied the association of clinical outcome and placental histopathology lesions with BW/PW ratios.

MATERIALS AND METHODS: During the period between 2008 and 2013, placentas from deliveries at gestational age (GA) ≥37 weeks, including both complicated and uncomplicated pregnancies, were sent for histopathology evaluation. Maternal and labor characteristics and pathological reports of the high BW/PW ratio group (>90th), normal BW/PW ratio group (10-90), and low BW/PW ratio group were compared (<10th).

RESULTS: The BW/PW ratio increased as GA increased, with an average GA of 39.4 ± 1.2 weeks in the normal BW/PW ratio group (p < 0.001). Patients with diabetes mellitus and smokers were more common in the low BW/PW ratio group (p < 0.001). Placental maternal stromal vascular lesions and villitis of unknown etiology (VUE) were more common in the high BW/PW ratio group (p < 0.001 and p = 0.03, respectively). By logistic regression analysis, GA, placental maternal stromal vascular lesions, and VUE were found to be independently associated with a high BW/PW ratio, while diabetes mellitus and smoking were independently associated with a low BW/PW ratio.

DISCUSSION: The BW/PW ratio increases significantly beyond 39th weeks, and is associated with an increased rate of placental maternal stromal vascular lesions and VUE.