A low-lying placenta, medically known as placenta praevia, occurs when the placenta implants in the lower segment of the uterus, partially or completely covering the opening of the cervix (cervical os). It is detected by ultrasound and can cause painless vaginal bleeding during pregnancy. The good news is that most cases of low-lying placenta diagnosed early in pregnancy resolve naturally as the uterus grows upward, usually by 28–32 weeks.
Low-lying placenta is called placenta praevia when it covers the cervical os (opening).
The main symptom is painless, bright red vaginal bleeding in the second or third trimester.
There are four types: low-lying, marginal, partial, and complete (total) praevia.
Most cases diagnosed early resolve by 28–32 weeks as the uterus grows upward.
Diagnosis is made by ultrasound — transvaginal ultrasound (TVS) is the most accurate.
Complete placenta praevia requires a caesarean section (C-section) delivery.
Risk factors include previous C-section, multiple pregnancies, age over 35, and smoking.
Placental migration refers to the apparent upward movement of the placenta as the lower uterus expands.
Normally, the placenta implants in the upper part (fundus) or on the sides of the uterus, away from the cervix. In low-lying placenta, the placenta attaches in the lower uterine segment. When the placenta edge is within 2 cm of the internal cervical os (opening of the cervix), it is called a low-lying placenta. When it partially or completely covers the cervical os, it is called placenta praevia. The placenta is responsible for supplying oxygen and nutrients to the baby through the umbilical cord, and its abnormal position can affect both delivery and the safety of the pregnancy.
Doctors classify placenta praevia into four types based on the degree to which the placenta covers the cervical os: Type 1 — Low-lying: The placenta is in the lower uterine segment but does not reach the internal os. The placental edge is within 2 cm of the os. Type 2 — Marginal praevia: The edge of the placenta just reaches the margin of the internal os but does not cover it. Type 3 — Partial praevia: The placenta partially covers the internal cervical os. Type 4 — Complete (Total) praevia: The placenta completely covers the internal cervical os. Complete placenta praevia almost always requires a caesarean section (C-section) delivery. The placenta can also be described by its wall position — anterior (front wall) or posterior (back wall).
The exact cause of low-lying placenta is not always known, but several factors increase the risk: Previous uterine surgery including caesarean section (C-section) scars, previous uterine surgeries, or D&C (dilation and curettage) procedures; multiple pregnancies (twins, triplets); being older than 35 years; smoking during pregnancy; having had a previous placenta praevia; uterine fibroids (non-cancerous growths) in the lower uterus; and carrying a large placenta, as is common in multiple pregnancies. Women who have had multiple pregnancies (multiparity) are at higher risk.
The hallmark symptom of placenta praevia is painless, bright red vaginal bleeding in the second or third trimester of pregnancy, typically after 20 weeks. The bleeding may be mild or heavy and may stop and restart. Unlike placental abruption, there is usually no abdominal pain. Other symptoms include the baby being in a transverse or breech position (because the placenta blocks the head from entering the pelvis). Diagnosis is made by ultrasound — either a transabdominal ultrasound (TAS) or a transvaginal ultrasound (TVS). Transvaginal ultrasound is more accurate for measuring the distance between the placental edge and the cervical os.
Management depends on the type, gestation, and whether there is bleeding. Most low-lying placentas diagnosed in the second trimester (18–20 week scan) resolve on their own by 28–32 weeks as the lower uterine segment grows upward — this process is called placental migration. A follow-up ultrasound at 32–36 weeks is usually recommended. If the placenta remains low-lying or praevia near term: bed rest and avoidance of sexual intercourse may be advised; hospitalization may be needed if there is significant bleeding; complete placenta praevia almost always requires a planned caesarean section at 36–38 weeks; blood transfusion may be needed if there has been heavy bleeding. Women with resolved low-lying placenta can usually deliver normally.
A low-lying placenta is when the placenta implants in the lower segment of the uterus, with its edge within 2 cm of the internal cervical os. If it covers the cervical os, it is called placenta praevia.
The main symptom is painless, bright red vaginal bleeding in the second or third trimester. There is usually no abdominal pain. The baby may also be in a transverse or breech position.
Yes, most cases of low-lying placenta detected at the 18–20 week scan resolve naturally by 28–32 weeks as the lower uterine segment grows and the placenta appears to move upward. A follow-up ultrasound confirms this.
If the placenta resolves and moves away from the cervix by 36 weeks, normal vaginal delivery is usually possible. Complete placenta praevia (placenta fully covering the cervix) requires a caesarean section.
Low-lying placenta is diagnosed by ultrasound. Transvaginal ultrasound (TVS) is the most accurate method and is safe during pregnancy. It measures the exact distance between the placental edge and the internal cervical os.
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