The placenta is an organ that develops within the uterus during pregnancy, connecting the birthing parent and the developing baby. It provides essential oxygen and nutrients to the fetus through the umbilical cord. The placenta also removes waste products, such as carbon dioxide, from the baby’s blood, functioning similarly to the baby’s lungs, kidneys, and liver until birth. This temporary organ also produces hormones that support fetal growth and helps transfer antibodies, contributing to the baby’s immunity.
Common Placenta Locations
The placenta can implant in various places on the uterine wall. An anterior placenta is located on the front wall of the uterus, closer to the abdomen. Conversely, a posterior placenta attaches to the back wall, closer to the spine.
A fundal placenta is situated at the top of the uterus. Lateral placentas implant on either the left or right side walls. These anterior, posterior, fundal, and lateral positions are normal variations.
A low-lying placenta, also known as placenta previa, occurs when the placenta implants in the lower part of the uterus, close to or covering the cervix.
Identifying Placenta Location on Ultrasound
Ultrasound imaging is the primary method used by medical professionals to determine the placenta’s location within the uterus. This assessment is commonly performed during the anatomy scan, which typically occurs between 18 and 22 weeks of pregnancy. During the ultrasound, the sonographer or doctor observes the placenta as a distinct, vascularized organ.
They carefully examine its position relative to the uterine walls and, importantly, its proximity to the cervix. Different ultrasound views, including transabdominal (over the abdomen) and sometimes transvaginal (if a clearer view of the cervix is needed, especially for low-lying placentas), are utilized to ensure precise identification. The medical professional will then communicate the findings regarding the placenta’s placement.
The placenta can appear homogeneous and uniformly echogenic on ultrasound, with a hypoechoic subplacental venous complex between the placenta and the uterine muscle (myometrium). As the pregnancy progresses, the uterus expands, and the placenta’s position can appear to change or “migrate” upwards, even though it remains anchored to the uterine wall. This apparent movement is due to the stretching and thinning of the lower uterine segment as the uterus grows.
Why Placenta Location Matters
For most common placenta placements, such as anterior, posterior, fundal, or lateral, there are typically no complications for the pregnancy or delivery. However, the location becomes important when the placenta is low-lying or, more specifically, in a condition called placenta previa.
Placenta previa can lead to potential risks, primarily vaginal bleeding, which can range from light to severe and may occur without pain. This bleeding happens because the placenta, rich in blood vessels, can separate slightly from the uterine wall as the cervix thins or dilates. Medical professionals closely monitor placenta previa, often recommending follow-up ultrasounds to see if the placenta moves away from the cervix as the uterus grows.
If placenta previa persists, especially if it completely covers the cervix, a vaginal delivery becomes unsafe due to the risk of significant hemorrhage. In such cases, a Cesarean section (C-section) is typically planned for delivery, often around 36 to 37 weeks of gestation, to ensure the safety of both the birthing parent and the baby. Management may also include avoiding heavy lifting, long-distance travel, and pelvic rest to minimize the risk of bleeding.