The placenta is a temporary organ that develops in the uterus during pregnancy, serving as the connection between the birthing parent and the developing fetus. Its primary function is to facilitate the exchange of oxygen, nutrients, and waste products between their separate bloodstreams. The placenta also produces hormones essential for maintaining the pregnancy and supporting fetal growth.
The placenta’s location within the uterus is important for prenatal care. Its position can influence the course of pregnancy and the safety of delivery. Healthcare providers routinely assess placental location through imaging to identify potential concerns.
Understanding Placental Location
The placenta typically attaches to the upper or side walls of the uterus. It connects to the fetus via the umbilical cord. The “internal os” refers to the opening of the cervix into the uterus, which is the passageway through which the baby exits during a vaginal birth.
If the placenta is positioned too close to the internal os, it can obstruct the birth canal, leading to complications during labor and delivery. Ultrasound is the primary method used to assess the placenta’s position and its relationship to the internal os. Transvaginal ultrasound offers a more accurate assessment.
What is a Normal Distance?
A placenta is generally considered to be in a normal or safe position when its lower edge is located more than 2 centimeters away from the internal os. This distance typically allows for a vaginal delivery without increased risk. If the placenta’s edge is within 2 centimeters of the internal os but does not cover it, the condition is referred to as a “low-lying placenta.”
Many low-lying placentas identified in early pregnancy (around 18-20 weeks) will shift upwards as the uterus grows and stretches. This phenomenon, often called “placental migration,” occurs as uterine growth pulls the placenta away from the cervix. About 90% of low-lying placentas resolve by the third trimester.
When the Placenta is Too Close
When the placenta completely or partially covers the internal os, the condition is known as placenta previa. This serious pregnancy complication can lead to significant bleeding. Placenta previa is classified based on how much of the internal os is covered: partial previa indicates it partially covers the opening, and complete previa means it fully covers it.
The most common symptom of placenta previa is painless, bright red vaginal bleeding, which typically occurs in the second or third trimester. This bleeding can range from light to heavy and may start, stop, and then restart. The primary concern with placenta previa is the risk of severe hemorrhage, as the placenta can block the baby’s exit, preventing a safe vaginal delivery.
Monitoring and Management
If a low-lying placenta or placenta previa is identified, healthcare providers will implement a monitoring and management plan. Regular follow-up ultrasounds are necessary to track the placenta’s position as the pregnancy progresses. These scans help determine if the placenta has moved away from the cervix, potentially allowing for a vaginal delivery.
Management strategies for placenta previa or a persistent low-lying placenta often involve precautions to reduce the risk of bleeding. These may include avoiding strenuous activities, refraining from sexual intercourse, and limiting digital vaginal examinations. In cases of placenta previa, a Cesarean section (C-section) is typically recommended for delivery to avoid severe bleeding that could occur during a vaginal birth. For a low-lying placenta, a vaginal birth might still be possible if the placental edge is sufficiently far from the internal os by the time of delivery.