An extra lobe on the placenta, known medically as a succenturiate lobe, develops when a portion of placental tissue grows separately from the main disc, connected to it only by membranes and blood vessels. The leading risk factors include assisted reproduction (particularly IVF), advanced maternal age, and a history of pelvic infections. The underlying mechanism appears to involve impaired blood supply to parts of the uterine lining, which forces the placenta to extend its reach by growing additional tissue at a distance from the primary disc. Reported in roughly 1 to 5 percent of pregnancies depending on how the diagnosis is made, a succenturiate lobe is not rare, but it does carry real clinical consequences that make early detection worthwhile.
How a Succenturiate Lobe Develops
In a typical pregnancy, the fertilized egg implants into the uterine wall and the placenta spreads outward from that point, forming a single, roughly circular disc. All the blood vessels feeding the placenta stay within or near this disc. A succenturiate lobe forms when part of the developing placenta encounters an area of the uterine wall that cannot adequately support it, whether because of scarring, poor blood flow, or some other localized problem. Instead of simply stopping growth in that direction, the placenta “skips” the inhospitable patch and establishes a satellite lobe elsewhere in the uterus where the blood supply is better.
This satellite lobe can be small or nearly as large as the main disc, and a pregnancy can have more than one. The extra lobe remains connected to the main placenta by blood vessels that run through the fetal membranes, and sometimes by a thin bridge of tissue. Those exposed vessels are the source of most complications, because they lack the protection that comes from being embedded in the thick placental body. Research describes this pattern as a “compensatory anatomical adaptation,” essentially the placenta solving a supply problem by spreading out rather than growing thicker in one spot.1PubMed Central. Diagnostic Challenges and Perinatal Outcomes: A Case Series on a Retrospective Study
Who Is Most at Risk
Three categories of risk come up repeatedly in the literature: assisted reproduction, older maternal age, and prior pelvic infections or uterine procedures. Each points back to the same basic mechanism of compromised uterine-lining quality.
- IVF and assisted reproduction: Women who conceive through IVF or similar techniques are diagnosed with succenturiate lobes more often than those who conceive spontaneously. One reason may be that the embryo is placed into the uterus at a slightly different stage of development or in a slightly different location than would occur with natural implantation. Additionally, many women who need fertility treatment have underlying conditions that already affect the uterine lining.
- Advanced maternal age: Older mothers show higher rates of this placental variant. The proposed explanation is gradual vascular deterioration in the uterus over time, meaning the blood vessels supplying the uterine wall become less efficient at supporting the growing placenta, pushing it to develop satellite tissue.1PubMed Central. Diagnostic Challenges and Perinatal Outcomes: A Case Series on a Retrospective Study
- Pelvic infections and uterine scarring: Past infections of the uterus or fallopian tubes can leave areas of the uterine lining damaged or scarred. Prior uterine surgeries, including cesarean sections, may have a similar effect. These scarred patches create the kind of “dead zones” that force the placenta to grow around them.
A case report of a 42-year-old woman who conceived via IVF illustrates how these factors can overlap. She had a history of multiple miscarriages and a hypercoagulable state (meaning her blood clotted more easily than normal), and a succenturiate lobe was detected during an ultrasound at around 13 weeks.2PubMed Central. Early sonographic detection of a succenturiate placenta after IVF in a 42-year-old woman with multiple comorbidities Her case hits three risk factors at once: advanced age, IVF conception, and underlying vascular issues. That kind of overlap is common in clinical practice.
There is also some evidence linking preeclampsia, a pregnancy complication involving high blood pressure, with succenturiate lobe formation. Whether preeclampsia causes the abnormal placental shape or the abnormal shape contributes to preeclampsia is an open question. It may go both ways: poor placental development could promote preeclampsia, and the vascular dysfunction behind preeclampsia could encourage the placenta to compensate by growing additional lobes.3International Journal of Women’s Health. Succenturiate Placental Lobe Abruption
How Prevalent Is It
Published estimates range widely. Some sources report a rate as low as about 0.16 percent of pregnancies, while others put it at around 5 percent when ultrasound is used systematically to look for it.4PubMed Central. Succenturiate Placental Lobe Abruption The large gap reflects how the condition is detected. Many succenturiate lobes go unnoticed during pregnancy and are only found when the placenta is examined after delivery, while dedicated imaging can pick up more cases. One review of ultrasound-based studies cited a 5 percent detection rate across all pregnancies scanned.5PubMed Central. Placental and Umbilical Cord Anomalies Diagnosed by Two- and Three-Dimensional Ultrasound The true figure likely sits somewhere in the middle: common enough that obstetricians encounter it regularly, but uncommon enough that many women go through pregnancy without it being mentioned.
How an Extra Lobe Is Detected
Most succenturiate lobes are spotted during the routine anatomy scan performed around 20 to 22 weeks of pregnancy. On ultrasound, the extra lobe appears as a separate mass of placental tissue, clearly distinct from the main disc and located some distance away from it. The technician or doctor can usually trace the blood vessels running between the two through the membranes. In a case series of nine pregnancies with succenturiate lobes, the majority were caught at this standard mid-pregnancy scan, which allowed the care team to adjust monitoring plans for the rest of the pregnancy.1PubMed Central. Diagnostic Challenges and Perinatal Outcomes: A Case Series on a Retrospective Study
Color Doppler ultrasound, which shows blood flow in real time, is particularly helpful. It makes the connecting vessels between the main placenta and the extra lobe visible, and it can reveal whether any of those vessels cross near or over the cervix, a complication called vasa previa. MRI has also been used to characterize unusual placental shapes, though it is not a first-line screening tool for this condition. In one study using MRI to examine abnormal placental shapes, succenturiate placenta was the single most common type identified, accounting for about half of the cases.6PubMed. Magnetic resonance imaging of abnormal placental shapes with correlation with pathologic findings
Early detection matters more here than for many other placental variants. If you know the extra lobe is there, you can check for vasa previa and plan around it. If you don’t, the risks described below arrive without warning.
The Velamentous Cord Connection
One of the most clinically important features of a succenturiate lobe is how the umbilical cord inserts. In a normal placenta, the cord attaches directly to the placental disc, and its vessels are protected by the thick tissue of the placenta itself. When a separate lobe exists, the blood vessels connecting the main disc to the satellite lobe run through the thin fetal membranes instead, unprotected. This arrangement is called velamentous cord insertion, and it showed up in a striking proportion of cases in recent research: out of nine succenturiate placenta diagnoses, four (about 44 percent) had velamentous cord insertion.1PubMed Central. Diagnostic Challenges and Perinatal Outcomes: A Case Series on a Retrospective Study
When those exposed vessels happen to cross the area near the cervix, the situation becomes vasa previa. If the membranes rupture, whether spontaneously or during labor, those unprotected vessels can tear, causing rapid fetal blood loss. This is a rare but potentially catastrophic event, and it is the main reason prenatal detection of a succenturiate lobe is so valuable. Finding the extra lobe early gives the clinical team time to check the position of those vessels and plan a cesarean delivery before labor starts if vasa previa is confirmed.7Ethiopian Journal of Reproductive Health. Succenturiate lobe of placenta with vasa previa: a case report of prenatal 4 diagnosis
Complications During Pregnancy and Delivery
Beyond vasa previa, a succenturiate lobe is linked to several other pregnancy complications. Research has tied it to higher rates of preeclampsia, fetal growth restriction, premature birth, placental abruption (where the placenta separates from the uterine wall too early), and emergency cesarean delivery. Low birth weight and, in serious cases, perinatal death are also reported at elevated rates compared to pregnancies with a normally shaped placenta.3International Journal of Women’s Health. Succenturiate Placental Lobe Abruption
The extra lobe’s position in the uterus matters, too. In one case, the succenturiate lobe was located in the lower part of the uterus, sitting close to the cervix. This mimicked a low-lying placenta and caused antepartum bleeding serious enough to require an emergency cesarean section.8Nigerian Hospital Practice. Succenturiate Placental Lobe Presenting with Antepartum Hemorrhage: A Case Report The bleeding came not from the main placenta, which was positioned normally in the upper uterus, but from the satellite lobe sitting where it could be disturbed by cervical changes. Without knowing the extra lobe was there, the clinical picture could easily be misinterpreted.
Not every succenturiate lobe causes problems. Many pregnancies with this finding proceed without incident, particularly when the lobe is small, the connecting vessels are short, and nothing crosses the cervix. The complications above represent elevated risks, not certainties. The clinical challenge is distinguishing the cases that will stay quiet from those that will not, which is why ongoing monitoring matters once the diagnosis is made.
Risks After Delivery
Even after the baby is born safely, a succenturiate lobe can cause trouble. The main postpartum concern is retained placenta: the main disc delivers normally, but the extra lobe remains attached to the uterine wall. Because the extra lobe is connected to the main placenta only by vessels and membranes, it can easily detach from the main disc during the third stage of labor without being pulled free of the uterus itself. If the delivering clinician doesn’t know the lobe exists, it may not be missed until symptoms develop.
Retained placental tissue prevents the uterus from contracting fully, which leads to bleeding. This can cause primary postpartum hemorrhage (heavy bleeding in the hours after delivery) or secondary postpartum hemorrhage (significant bleeding days or weeks later, once the retained tissue begins to break down or becomes infected).9Journal of Case Reports and Images in Obstetrics and Gynecology. Succenturiate placenta: An incidental finding Postpartum infection of the uterus, called endometritis, is also more likely when tissue is left behind.
The practical takeaway for delivery teams is to inspect the placenta carefully after every birth. A gap in the membranes, vessels that seem to lead nowhere at the edge of the disc, or an irregularly shaped placental margin all suggest that an extra lobe may still be inside. If prenatal ultrasound has already flagged a succenturiate lobe, the team can specifically check that it has been delivered along with the main placenta. This is one of the clearest examples in obstetrics of how a prenatal diagnosis directly changes the safety of postpartum care.
How Extra Lobes Differ from a Bilobed Placenta
A succenturiate lobe is sometimes confused with a bilobed placenta, but the two are distinct conditions. A bilobed placenta consists of two roughly equal-sized lobes, both of substantial size, separated by membranes. Its incidence is estimated at about 2 to 8 percent of placentas.5PubMed Central. Placental and Umbilical Cord Anomalies Diagnosed by Two- and Three-Dimensional Ultrasound A succenturiate lobe, by contrast, is notably smaller than the main disc. It is an accessory, not a co-equal partner.
There is also a rarer entity called a “true accessory lobe,” which differs from a succenturiate lobe in that it connects to the main placenta through full-thickness tissue rather than just vessels running through the membranes. This structural difference may make it less prone to being retained after delivery, because the thicker connection allows it to separate from the uterine wall along with the main disc.10Journal of Case Reports and Images in Obstetrics and Gynecology. A true accessory placental lobe: Two case reports of a novel morphological placental anomaly, distinct from succenturiate and bilobed placenta In practice, the distinction between these variants is often only clear after delivery, when the placenta can be physically examined. During pregnancy, ultrasound may show “extra placental tissue” without being able to specify exactly which type it is.
What Happens After a Diagnosis
If your mid-pregnancy ultrasound reveals a succenturiate lobe, the immediate next step is typically a detailed Doppler scan to map where the connecting vessels run. The question the clinical team wants to answer is whether any vessels cross near the cervix. If they do, you are likely looking at a planned cesarean delivery before labor begins, to protect those vessels from rupturing. If the vessels are well away from the cervix, vaginal delivery usually remains an option, though the team will note the finding and watch for it at delivery.
Beyond vessel mapping, the pregnancy will typically involve closer monitoring for some of the associated complications. Growth scans may be scheduled more frequently to check that the baby is growing on track, since fetal growth restriction is more common with this placental shape. Blood pressure monitoring for preeclampsia, which was already part of routine care, may receive extra attention. None of this means complications are inevitable; it means the care team is accounting for a known risk rather than being caught off guard.
During delivery, the medical team should inspect the placenta after it is delivered and confirm that all lobes are accounted for. If a piece appears to be missing, or if membranes show torn vessels at their edges, manual exploration of the uterus or ultrasound can help determine whether tissue has been retained. When a succenturiate lobe has been identified prenatally, this step goes from a general precaution to a specific, targeted check. That shift from general vigilance to focused action is probably the single biggest clinical benefit of catching the extra lobe early.