Background:
Women with type 1 and type 2 diabetes are at high risk of pregnancy complications including gestational hypertension, pre-eclampsia and intra-uterine growth restriction (IUGR) with the placenta mediating many of these outcomes. Structural changes in the placenta have been assessed with ex-vivo tissue sampling, histopathological examination and immunohistochemistry. More recently, in-vivo assessment of placental change has been studied using ultrasound-based shear wave elastography (a routine diagnostic tool to estimate fibrosis in chronic liver disease). We aimed to investigate the role of placental elastography in women at very "high risk" - those with type 1 or type 2 diabetes prior to conception.
Methods:
We conducted two distinct literature searches to broadly capture all relevant published data. Our first search was to summarize the known histopathologic changes in placentas of women with type 1 or type 2 diabetes. Our search terms included “Diabetes mellitus” AND “placenta” AND “histopathology”. Our second search used the terms, “(elastography OR stiffness OR Elasticity OR kpa OR kilopascals) AND placenta” to capture and summarize structural placental changes detectable by elastography. To estimate the increasing stiffness with ‘high risk’ pregnancies, we conducted a meta-analysis of 16 relevant studies that reported stiffness in metres per second (m/s) OR kilopascals (kPa).
Results:
After screening, we identified 57 studies for full text review of histopathology in women with type 1 or type 2 diabetes published between 1969 and 2017. There is a wide variety of histopathologic changes described in women with diabetes, however none are considered pathognomonic, and indeed some may be shared common processes with other conditions such as hypertension or IUGR. Broadly, histopathological changes are divided into categories based on presumed aetiology including maternal malperfusion, fetal malperfusion, infectious/inflammatory.
After screening, we identified 16 relevant studies (with reports of stiffness values) to be included in meta-analysis. In-vivo placental elastography may detect a difference in stiffness scores for many women with a "high-risk" pregnancy. The mean difference for maternal-derived pathologies was 4.5kPa (95% CI 3.16 - 5.87) and for fetal-derived pathologies 6.5kPa (95% CI 1.08 – 11.86). Very few of these studies included women with pre-existing diabetes (we identified less than 10 participants with pre-existing type 1 and/or type 2 diabetes across the 16 studies).
Conclusion:
Placental stiffness measurements may provide an in-vivo approximation of placental histopathology in women with diabetes. Placental elastography might be useful in studying whether diabetes, pre-eclampsia and IUGR share common pathways to structural placental changes.