Probability distributions of placental morphological measurements and origins of variability of placental shapes

• Published in: Placenta (Eastbourne) 2013-06, Vol.34 (6), p.493-496
• Main Authors: Yampolsky, M, Salafia, C.M, Shlakhter, O
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Chorionic plate; Embryology: invertebrates and vertebrates. Teratology; Female; Fundamental and applied biological sciences. Psychology; Humans; Internal Medicine; Log-normal distribution; Normal distribution; Obstetrics and Gynecology; Organ Size; Photography; Placenta - anatomy & histology; Placenta - blood supply; Placental shape; Placentation; Power law; Pregnancy; Pregnancy. Parturition. Lactation; Probability; Stochastic growth; Umbilical Cord - anatomy & histology; Vertebrates: reproduction
• ISSN: 0143-4004; 1532-3102
• DOI: 10.1016/j.placenta.2013.03.003

Abstract Introduction While the mean shape of human placenta is round [1] with centrally inserted umbilical cord, significant deviations from this ideal are fairly common, and may be clinically meaningful [1] . Traditionally, they are explained by trophotropism. We have proposed a hypothesis explaining typical variations in placental shape by randomly determined fluctuations in the growth process of the vascular tree. It has been recently reported that umbilical cord displacement in a birth cohort has a log-normal probability distribution, which indicates that the displacement between an initial point of origin and the centroid of the mature shape is a result of accumulation of random fluctuations of the dynamic growth of the placenta. To confirm this, we investigate statistical distributions of other features of placental morphology. Methods In a cohort of 1023 births at term digital photographs of placentas were recorded at delivery. Excluding cases with velamentous cord insertion, or missing clinical data left 1001 (97.8%) for which placental surface morphology features were measured. Best-fit statistical distributions for them were obtained using EasyFit. Results and discussion The best-fit distributions of umbilical cord displacement, placental disk diameter, area, perimeter, and maximal radius calculated from the cord insertion point are of heavy-tailed type, similar in shape to log-normal distributions. This is consistent with a stochastic origin of deviations of placental shape from normal. Conclusions Deviations of placental shape descriptors from average have heavy-tailed distributions similar in shape to log-normal. This evidence points away from trophotropism, and towards a spontaneous stochastic evolution of the variants of placental surface shape features.