Finding two placentas with a single baby during pregnancy can be unexpected. While one placenta typically supports one baby, variations in placental development can lead to the appearance of two distinct placental masses, even with a singleton pregnancy. This article clarifies what having two placentas means, how such variations develop, and the monitoring and care involved.
What Having Two Placentas Means
When an ultrasound indicates “two placentas” with one baby, it usually refers to a specific anatomical variation of a single placenta, rather than two entirely separate organs. These variations are often described as a bilobed placenta or a succenturiate lobe.
A bilobed placenta consists of two lobes that are roughly equal in size, connected by membranes and blood vessels. In contrast, a succenturiate lobe involves a main placental mass with one or more smaller, accessory lobes that are separate but connected by blood vessels running through the membranes. These conditions are variations in the placenta’s structure and do not typically imply a vanished twin, though in some cases, a vanished twin can result in extra placental tissue. While these placental forms are not associated with a higher risk of fetal abnormalities, they warrant careful attention due to potential implications for the pregnancy.
How Two Placentas Develop
Variations like bilobed or succenturiate placentas arise from how the placenta grows and attaches within the uterus. Uneven growth or implantation in areas of reduced blood supply can contribute to the formation of separate lobes. Factors such as implantation over uterine fibroids, previous uterine surgery sites, or the cervical opening can also influence the placenta’s shape. Advanced maternal age and pregnancies resulting from in vitro fertilization (IVF) are sometimes associated with an increased incidence of succenturiate placentas. These developmental patterns result in a placenta that appears as two distinct parts, connected by vessels that traverse the fetal membranes.
Monitoring During Pregnancy
For pregnancies involving a bilobed or succenturiate placenta, healthcare providers typically recommend increased monitoring to ensure the well-being of both the baby and the pregnant individual. More frequent ultrasounds assess fetal development, amniotic fluid levels, and blood flow through the placenta and connecting vessels.
A primary concern with these placental variations is vasa previa, a condition where fetal blood vessels connecting the lobes or running from the umbilical cord cross near the internal cervical opening. If these unprotected vessels are located over the cervix, they are at risk of compression or rupture during labor, which could lead to rapid fetal blood loss. Therefore, careful ultrasound evaluation, particularly with color Doppler, is performed to identify the location of these vessels. While many pregnancies with these placental forms proceed without complications, the increased monitoring allows for early detection and management of potential issues such as placental abruption, retained placental tissue, or preterm labor.
Delivery and Postpartum
The presence of a bilobed or succenturiate placenta influences the planning and management of delivery and the immediate postpartum period. Healthcare providers carefully consider the location of the placental lobes and any connecting vessels, especially if vasa previa has been identified. In cases of vasa previa, an elective cesarean delivery is often recommended to prevent the rupture of fetal vessels during labor, typically planned between 34 to 36 weeks of gestation.
After the baby is born, complete removal of all placental tissue is important. A thorough examination of the delivered placenta(s) confirms that all lobes, including any accessory lobes, have been expelled. Retained placental fragments can lead to complications such as postpartum hemorrhage or infection. Postpartum monitoring may include observation for excessive bleeding.