The placenta is the baby's lifeline, facilitating the transfer of oxygen and nutrients as well as hormones between mother and fetus without mixing the two.
There are several things that can go wrong with the placenta at each stage of pregnancy — two of which are placenta previa and placental abruption.
Placenta Previa vs. Abruption
Placenta previa and placental abruption are disorders of the placenta typically marked by vaginal bleeding, among other symptoms, and they can both be life-threatening to mother and baby.
The key difference is that placenta previa is a problem with where the placenta attaches to the uterus while placental abruption is a problem stemming from the premature detachment of the placenta from the uterine wall.
Here is what to know about each condition, how they are diagnosed, and what doctors do to treat them.
What Is Placenta Previa?
Placenta previa affects 1 in 200 pregnancies and is the leading cause of postpartum hemorrhage. Women who have had previous pregnancies and especially prior c-sections are at increased risk. Asian women living in the U.S. are 86% more likely than white women to have a pregnancy complicated by placenta previa [*].
Placenta previa is typically diagnosed after 20 weeks’ gestation when a low-lying placenta fails to migrate upwards with the growth of the fetus. About 10-15% of placentas are low-lying at the 18-20 week ultrasound but only 0.5% are still low-lying at term. Women with a low-lying posterior placenta location are more likely to have placenta previa than those with an anterior low-lying placenta. Women with placenta previa in an anterior position are more likely to experience hemorrhaging.
Placenta Previa Symptoms
Painless bleeding in the second half of pregnancy is the classic presentation of placenta previa. The bleeding (bright red) usually occurs as the uterus thins in the last trimester to prepare for labor. The percentage of women who bleed before 30 weeks, between 30 and 36 weeks, and after 36 weeks, is evenly divided. If you are bleeding for any reason, with or without pain, during your pregnancy, contact your care provider immediately.
A previous c-section increases your risk of placenta previa, and having placenta previa following a prior c-section is associated with high and increasing risk of PAS (placenta accreta syndromes), where the placenta attaches too deeply to the uterine wall [*].
Placenta Previa Diagnosis
Placenta previa can be diagnosed and monitored via ultrasound scan. The first indication is a low-lying placenta, but most placentas that begin low-lying don’t stay that way. The placenta “migrates” as the fetus grows. It doesn’t actually pick up and move when it migrates, but its central part grows toward better blood supply at the top of the uterus while its end portions in the less blood-rich, lower segment of the uterus regress and atrophy. This is the normal course of events for 90% of low-lying placentas.
Placenta Previa Treatment
The placenta cannot be moved once it has been implanted. Your care team will monitor the placenta location and treat you with the aim of getting you as close to full-term as possible.
Exercise, lifting more than 15 pounds, pelvic exam, and sexual activity may all be restricted. In some cases, bed rest or hospitalization will be required to avoid the possibility of hemorrhage or preterm birth.
Placenta previa usually requires a c-section to avoid maternal hemorrhage during delivery.
What Is Placental Abruption?
Placental abruption (also called placenta abruptio) is more common than placenta previa. It occurs in 1 in 100 pregnancies. 4 out of 5 women will experience vaginal bleeding from placental abruption, but it sometimes goes undetected when the blood is trapped behind the placenta.
Mild cases — where only a very small part of the placenta separates from the uterine wall — usually aren’t dangerous but need to be monitored to ensure the separation doesn't get bigger.
In cases that are not mild, the fetus is at greater risk for growth problems due to intrauterine restriction, preterm birth (1 in 10 preterm births are from abruption), and stillbirth [*].
Placental abruption may occur in a chronic manner or suddenly, with or without a specific trauma, such as a fall or car accident.
Maternal complications from placental abruption can include life-threatening anemia, hemorrhage, and a deadly blood clotting issue called DIC (disseminated intravascular coagulation) where clotting factors from the placenta are rapidly distributed into the mother’s bloodstream, causing it to try to counterbalance with anti-clotting factors that exacerbate hemorrhaging.
Maternal mortality from abruption is rare (.5 - 1%) but fetal mortality is very high (20-70%) depending on how severe the separation is, what caused the separation, and the gestational age of the fetus.
Placental Abruption Symptoms
Symptoms of placental abruption include (dark red) vaginal bleeding in 80% of cases, usually with abdominal pain ranging from discomfort or tenderness to constant belly or back pain. In more severe cases there may be contractions that won’t relax (tetany). It most commonly presents at 24-26 weeks [*].
There are grades of severity based on the nature of the mother’s symptoms, the health of the fetus, and how much of the placenta has separated from the uterine wall.
- Grade 1 - less than 100ml of uterine bleeding, non-tender uterus, reassuring fetal status;
- Grade 2 - tender uterus, fetal distress, concealed hemorrhage; and
- Grade 3 - fetal death, maternal shock, extensive concealed hemorrhage. Severe grades of abruption are more often seen in African-American and white women than Asian or Latin-American women [*].
Placental Abruption Diagnosis
Placental abruption is usually diagnosed by the clinical symptoms presented by the mother. An ultrasound may be performed to rule out placenta previa and to see if the site of detachment can be seen, but it’s important to note that roughly half of patients with abruptions may not show them on ultrasound.
Placental Abruption Treatment
There is no treatment to reattach the placenta. Once abruption has been diagnosed, your care team will consider your treatment in view of the severity of the condition and the gestational age and status of the fetus. Vaginal labor may be possible if the fetus is not in distress.
In minor cases, your care team may suggest bed rest to mitigate bleeding, allowing you to resume your normal activities after a few days.
In moderate cases, a hospital stay is likely so your care team can monitor you and your fetus. A blood transfusion may be needed, and if the fetal heart rate indicates distress, your doctor may induce early delivery, either vaginally or via c-section.
In severe cases, your doctor will deliver your baby immediately, usually by c-section, especially if there is any sign of fetal distress. In about 1 in 800 pregnancies, placental abruption causes a stillbirth.
Differences Between Placenta Previa and Abruption
These are a few of the ways placenta previa and abruption differ, but keep in mind this is merely a guideline based on classic presentations. Any bleeding during pregnancy should be referred to your care team immediately.
|Placenta Previa||Placental Abruption|
|Blood color||Bright red||Dark red|
|Bleeding||70% of cases||Hidden in 20% of cases|
|Pain||10-20% of cases||Abdominal pain, tender uterus, common|
|Contractions||Not typically seen||In moderate and severe cases|
|Cause of bleeding||Attachment issue: Low position in uterus covering cervix||Detachment issue: early separation from any location in the uterus|
|Risk Factors in common||
|Distinct Risk Factors||
|When Diagnosed||After 20 weeks, evenly split thereafter||Highest incidence of cases present at 24-26 weeks [*]|
|How Diagnosed||Ultrasound scan||Clinical symptoms + ultrasound mainly to rule out previa|
|Associated with||Preterm birth, low birthweight, lower APGAR scores, longer hospitalization, higher blood transfusion rates. When combined with prior history of c-section, risk of placenta accreta is elevated.||Preterm birth, delivery room resuscitation, neonatal apnea, neonatal respiratory distress syndrome [*], fetal neurological issues (10-15%)|
Placenta previa and placental abruption may both present initially with vaginal bleeding but their root causes and impact on mother and baby are very different.
Both these issues can be life-threatening to mother and baby if they go undetected. If you experience vaginal bleeding while you’re pregnant, contact your care team immediately or go to a hospital for evaluation.
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