Model Answer
0 min readIntroduction
The placenta is a temporary organ that connects the developing fetus to the uterine wall, allowing for nutrient uptake, waste elimination, and gas exchange. Its development and morphology are crucial for a healthy pregnancy outcome. A full-term placenta, typically delivered after 37-40 weeks of gestation, exhibits specific characteristics. However, congenital malformations of the placenta can occur, leading to various complications. Understanding these features and anomalies is vital for obstetricians and pediatricians to manage pregnancies and neonatal care effectively.
Morphological Features of a Full-Term Placenta
A full-term placenta typically presents with the following characteristics:
- Shape: Generally discoid or circular, though variations can occur.
- Size: Approximately 15-25 cm in diameter.
- Weight: Around 500-600 grams (varies with gestational age and fetal weight).
- Thickness: Approximately 2-3 cm.
- Maternal Surface: Divided into 15-20 cotyledons by septa. These cotyledons appear convex and are remnants of the uterine implantation sites.
- Fetal Surface: Smooth and shiny, covered by the amnion. The umbilical cord inserts centrally or eccentrically.
- Umbilical Cord: Typically 50-60 cm long, with an average diameter of 1-2 cm. It contains two arteries and one vein.
- Membranes: Composed of the amnion and chorion. The chorion laeve covers the placental surface, while the chorionic frondosum forms the villi.
- Villi: Finger-like projections extending from the chorionic plate into the maternal blood spaces. They are the functional units of the placenta, facilitating exchange.
Congenital Malformations of the Placenta
Several congenital malformations can affect the placenta. Here are five examples:
1. Placenta Previa
Description: The placenta implants in the lower uterine segment, partially or completely covering the internal cervical os. Clinical Significance: Causes painless vaginal bleeding in the third trimester, potentially leading to preterm labor and requiring cesarean delivery. Incidence: Approximately 0.5-1% of pregnancies (based on knowledge cutoff 2023).
2. Placental Abruption
Description: Premature separation of the normally implanted placenta from the uterine wall. Clinical Significance: Can cause significant maternal and fetal hemorrhage, fetal distress, and preterm labor. Risk Factors: Hypertension, trauma, smoking.
3. Single Umbilical Artery (SUA)
Description: The umbilical cord has only one artery instead of the usual two. Clinical Significance: Often associated with other congenital anomalies, such as cardiac defects and chromosomal abnormalities. Requires careful fetal monitoring. Incidence: Approximately 1% of pregnancies.
4. Velamentous Cord Insertion
Description: The umbilical cord inserts into the membranes rather than the placental disc. The vessels run unprotected within the membranes. Clinical Significance: High risk of vessel rupture during labor, leading to fetal hemorrhage and hypoxia. Diagnosis: Usually detected on ultrasound.
5. Placenta Accreta Spectrum (PAS)
Description: A range of conditions where the placenta abnormally adheres to the uterine wall. Includes placenta accreta (attaches to myometrium), increta (invades myometrium), and percreta (penetrates through myometrium). Clinical Significance: Severe risk of postpartum hemorrhage, often requiring hysterectomy. Risk Factors: Prior cesarean delivery, advanced maternal age.
Table summarizing the malformations:
| Malformation | Description | Clinical Significance |
|---|---|---|
| Placenta Previa | Implantation in lower uterine segment | Painless bleeding, preterm labor |
| Placental Abruption | Premature placental separation | Hemorrhage, fetal distress |
| SUA | Single umbilical artery | Associated anomalies, monitoring needed |
| Velamentous Insertion | Cord inserts into membranes | Vessel rupture, fetal hemorrhage |
| PAS | Abnormal placental adherence | Postpartum hemorrhage, hysterectomy |
Conclusion
The full-term placenta exhibits distinct morphological features essential for fetal development. However, congenital malformations can significantly compromise pregnancy outcomes. Early detection through prenatal imaging, such as ultrasound, and appropriate management strategies are crucial for minimizing maternal and fetal morbidity and mortality. Continued research into the etiology and prevention of these anomalies remains a priority in obstetrical care.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.