Normal Anatomy and Variations of the Placenta
The placenta is a vital temporary organ that facilitates nutrient, gas, and waste exchange between the mother and the fetus. A normal term placenta is discoid in shape, weighs about 500 grams, and measures roughly 20 centimeters in diameter. Morphological variations can occur during development without necessarily impairing function.
- Placenta succenturiata: Presence of one or more accessory lobes connected to the main placenta by blood vessels. Retained lobes post-delivery can cause severe postpartum hemorrhage.
- Placenta bilobata: The placenta is divided into two roughly equal lobes, with the umbilical cord inserting between them.
- Circumvallate placenta: The fetal surface is double-folded at the periphery, creating a dense, raised white ring. This increases the risk of antepartum hemorrhage and preterm labor.
Abnormalities of Placental Implantation
Placental implantation refers to the location where the blastocyst implants within the uterine cavity. When implantation occurs in the lower uterine segment rather than the upper body, complications arise.
- Placenta praevia: The placenta implants in the lower uterine segment, partially or completely covering the internal cervical os. It presents classically as painless vaginal bleeding in the third trimester.
- Low-lying placenta: The placental edge approaches the internal cervical os but does not cover it.
Low-lying placentas diagnosed early in pregnancy often migrate upward as the lower uterine segment stretches in the second and third trimesters. Vaginal examinations are strictly contraindicated in suspected placenta praevia to prevent catastrophic hemorrhage.
Spectrum of Invasive Placentation
Invasive placentation occurs when villous tissue invades the myometrium due to a deficient decidua basalis layer, frequently associated with prior uterine scars such as previous cesarean sections.
- Placenta accreta: Villae attach directly to the myometrium without invading the muscle. This is the most common form.
- Placenta increta: Villae invade deeper into the myometrium muscle wall.
- Placenta percreta: Villae penetrate completely through the myometrium and can invade surrounding structures like the urinary bladder.
Management of these conditions often requires planned cesarean hysterectomy to prevent fatal maternal hemorrhage.
Umbilical Cord Insertion Abnormalities
The site where the umbilical cord inserts into the placental mass affects fetal wellbeing and delivery safety.
- Battledore insertion: The cord inserts at the margin or edge of the placenta rather than the center. It has minimal clinical significance unless the margin tears during delivery.
- Velamentous insertion: The umbilical cord inserts into the fetal membranes rather than the placental mass, leaving the unprotected blood vessels (vasa praevia) to course across the internal cervical os.
When membranes rupture in vasa praevia, the unsupported fetal vessels can tear, leading to rapid fetal exsanguination and demise.
Pathological Conditions and Infarctions
Various degenerative and pathological changes can affect the placental tissue during gestation, altering its functional capacity.
- Placental infarctions: Areas of ischemic necrosis caused by interruption of maternal blood flow in the intervillous space. Small focal infarcts are normal at term, but extensive infarctions indicate uteroplacental insufficiency.
- Chorioamnionitis: Bacterial infection of the fetal membranes and chorionic plate, usually ascending from the lower genital tract after membrane rupture.
- Placental calcification: Deposition of calcium salts, commonly seen near term as a sign of placental aging and maturity.
Clinical Presentation and Diagnostic Evaluation
Identifying placental abnormalities early helps prevent life-threatening complications for both mother and fetus. Ultrasound is the primary diagnostic modality used during routine antenatal care.
- Transabdominal and transvaginal ultrasonography: Used to locate the placental edge relative to the internal cervical os and assess myometrial invasion depth.
- Color Doppler imaging: Essential for identifying abnormal vascular patterns in suspected invasive placentation or vasa praevia.
- Magnetic resonance imaging (MRI): Utilized when ultrasound findings are inconclusive, especially for deep myometrial or parametrial invasion.
Maternal stabilization, serial hemoglobin monitoring, and avoiding digital cervical exams remain standard protocols when bleeding is present.
Maternal and Fetal Complications
Abnormalities of the placenta carry significant morbidity and mortality risks for both the mother and the developing fetus.
- Maternal complications: Massive postpartum hemorrhage, hemorrhagic shock, disseminated intravascular coagulation, emergency peripartum hysterectomy, and surgical injury to adjacent pelvic organs like the bladder.
- Fetal complications: Fetal growth restriction due to poor perfusion, chronic hypoxia, preterm birth complications, fetal anemia from vasa praevia bleeding, and intrauterine fetal demise.
Prompt recognition and multidisciplinary team intervention significantly improve clinical outcomes.
Nursing Management and Collaborative Care
Comprehensive nursing care focuses on vigilant monitoring, early detection of complications, and emergency preparedness.
- Vital signs and hemodynamic monitoring: Assess maternal pulse, blood pressure, and oxygen saturation regularly to detect early signs of hypovolemic shock.
- Bleeding assessment: Weigh pads, monitor vaginal discharge closely, and report active hemorrhage immediately.
- Fetal surveillance: Perform continuous fetal heart rate monitoring to assess for signs of fetal distress.
- Emergency readiness: Ensure large-bore intravenous access is patent, cross-matched blood is available, and emergency surgical trays are accessible.
Nurses also provide emotional support to the mother and her family while coordinating rapid care with obstetricians, anesthetists, and pediatricians.