Small placental size is common in stillbirths, including unexplained late-gestation stillbirths

OBJECTIVES: This study determined if placentas with low weight and/or abnormal size were associated with an increase in stillbirth incidence, and if the proportion of small placentas was greater in 'unexplained' late-gestation stillbirth. METHODS: A total of 390 fresh, trimmed, placentas from stillbirths were weighed and measured. The Perinatal Society of Australia and New Zealand (PSANZ) Perinatal Death Classification (PDC) system (2018) was used for cause-of-stillbirth categories. A generalised linear model with a log link and a binomial distribution was used to assess how the risk of a small placenta varied according to potential explanatory factors. RESULTS: Small placentas were 7-times more common in this stillbirth cohort when compared to livebirths. Babies who were stillborn at term were more likely than those born preterm to have a small placenta (RR 1.7; 95 % CI 1.1-2.4) and low placental weight to birthweight ratio (RR 2.7; 95 % CI 1.7-4.2). There were 117 (30.0 %) stillbirths classified as 'unexplained', and the adjusted RR (aRR) of having an unexplained stillbirth with a small placenta was 1.6 (95 % CI 1.1-2.2). Furthermore, there was a 20 % increase in the risk of small placenta for women who had a peripheral cord insertion (aRR 1.2; 95 % CI 1.0-1.3). CONCLUSIONS: Stillbirths were associated with small placentas, low placental weight, low placental volume and low placental weight to birthweight ratio. Furthermore, we established a link between abnormal cord insertion and low placental weight in stillbirths, as well as between unexplained stillbirths and small placentas.