Placental Pathology I: Basics for the OB/GYN

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Reading: https://www.contemporaryobgyn.net/view/placental-pathology-it-time-get-serious 

  • Great article for this! 

What do we hope to get by sending a placenta to pathology? 

We want to know what happened! 

The goals are to get: 

  • Findings that are relevant to the immediate care of the mother or baby

  • Findings predictive of possible recurrence that could guide pregnancy care in subsequent pregnancies 

  • Diagnoses that explain adverse pregnancy events (probably the most common reason we send a placenta) 

  • Findings that may be important in medico-legal investigation of perinatal mortality and long-term morbidity 

So… which placentas should we send? 

There are many reasons, and some of them may depend on your institution, but we have broken this down into three categories 

  • Maternal reasons 

    • Preterm delivery

    • Unexpected or recurrent pregnancy complications 

    • Maternal systemic disorders (ie. preeclampsia, malignancy, diabetes, etc) 

    • Infection

    • Excessive third-trimester bleeding 

  • Fetal reasons 

    • Stillbirth, neonatal death 

    • Unexpected NICU admission 

    • SGA or LGA 

    • pH <7.0. 5-minute Apgar <7, or birth depression 

    • Neonatal seizures 

    • Hydrops, severe oligo/poly 

    • Multiple gestation 

  • Placental reasons 

    • Structural abnormalities or size abnormalities 

    • Possible incomplete placenta 

  • We can see that some of these reasons may not present until after the first day of life, so would recommend holding the placenta for up to 7 days if needed (can be stored unfixed in a fridge for that long!) 

The Anatomy and Development of the Placenta 

www.placentalab.org

We are going to first discuss a full-term placenta and then go over embryology

  • The placenta can be thought of as three layers:

    • Maternal side (basal plate) 

      • Contains trophoblastic cells and decidual cells and contain the decidua basalis 

      • From the basal plate, the placenta septa bulge into the intervillous space, creating a system of grooves 

      • Basal plate is also penetrated by endometrial arteries and venules 

    • Intervillous space - separates the maternal and fetal side 

      • Exchange between the fetal and maternal circulatory systems occur between the main stem villi and the maternal endometrial arteries and venules in this space 

      • Remember: fetal and maternal blood don’t mix! 

    • Fetal side (chorion plate)  

      • Made of connective tissue and contains the amnion, the main stem villi, and chorionic arteries and veins, which then coalesce at the cord insertion site → umbilical cord 

      • The chorionic arteries and veins → arterioles and venules of the main stem villi 

      • The main stem villi project into the intervillous space and are connected to the maternal basal plate by anchoring villi 

  • Placental embryology - super basic 

    • After fertilization and implantation, around day 5, the blastocyst is formed 

    • The blastocyst will eventually implant, and will contain the blastocyst cavity, the inner cell mass, and the trophoblast (which becomes the placenta) 

    • During implantation, there are complex interactions between the endometrium and the embryo → apposition, adhesion, and invasion 

      • Any dysfunction in these 3 processes can lead to abnormal placentation that can lead to affected placental function