The placenta is a temporary organ that develops in the uterus during pregnancy. It attaches to the uterine wall and serves as a vital connection between the pregnant person and the developing baby. Through the umbilical cord, the placenta delivers oxygen and nutrients to the fetus while also removing waste products, functioning as the baby’s lungs, kidneys, and liver before birth.
Understanding Placenta Locations
The placenta can attach to various areas within the uterus, and several positions are considered common. An anterior placenta is located on the front wall of the uterus, closer to the abdomen. This position is observed in up to 50% of pregnancies. A posterior placenta attaches to the back wall of the uterus, closer to the spine, and is also very common, occurring in approximately 50-60% of pregnancies.
Other normal locations include a fundal placenta, positioned at the top of the uterus, and a lateral placenta, situated on either the left or right side of the uterine wall. For most pregnancies, there is no single “best” or ideal position among these common placements. The location where the fertilized egg implants into the uterine wall determines the initial placental position. An anterior placenta might cushion fetal movements, making them harder to feel early on, while a posterior placenta might allow for earlier and stronger detection. These are normal variations that do not affect the baby’s health or development.
When Placenta Position Requires Attention
Certain placental positions, however, warrant closer medical attention due to potential complications. A low-lying placenta occurs when the placenta attaches to the lower part of the uterus, with its edge less than 2 centimeters from the opening of the cervix, but not covering it. This condition is often identified during the mid-pregnancy ultrasound scan. While a low-lying placenta can increase the risk of bleeding, particularly later in pregnancy or during labor, it frequently resolves on its own as the uterus grows and expands.
Placenta previa is a more significant condition where the placenta partially or completely covers the cervix. This can lead to serious complications, including painless vaginal bleeding in the second half of pregnancy, which can be severe. Placenta previa has classifications: marginal (edge at cervical opening but not covering), partial (partially covers cervix), and complete or total (fully blocks cervical opening). Complete previa carries the highest risk of severe bleeding and typically necessitates a cesarean delivery. Other risks associated with placenta previa include premature birth.
Monitoring and Management of Placenta Position
The position of the placenta is typically determined during a routine anatomy ultrasound scan, usually performed between 18 and 21 weeks of pregnancy. If the placenta is found to be low-lying at this time, follow-up ultrasounds are often recommended. These additional scans, commonly at 32 weeks and sometimes 36 weeks, monitor whether the placenta has moved upwards and away from the cervix as the uterus expands.
For cases of placenta previa that do not resolve, management strategies focus on monitoring the pregnant person and baby to minimize risks. This may involve recommendations for reduced activity, avoiding sexual intercourse, and careful observation for any bleeding. A planned cesarean delivery is typically required for individuals with persistent placenta previa, due to the risk of significant bleeding during labor.