Placenta previa
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Placenta previa
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Male and female reproductive system disorders
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Placenta previa
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Reproductive system pathology review
Disorders of sex chromosomes: Pathology review
Prostate disorders and cancer: Pathology review
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Uterine disorders: Pathology review
Ovarian cysts and tumors: Pathology review
Cervical cancer: Pathology review
Vaginal and vulvar disorders: Pathology review
Benign breast conditions: Pathology review
Breast cancer: Pathology review
Complications during pregnancy: Pathology review
Congenital TORCH infections: Pathology review
Disorders of sexual development and sex hormones: Pathology review
Amenorrhea: Pathology Review
Testicular and scrotal conditions: Pathology review
Sexually transmitted infections: Warts and ulcers: Pathology review
Sexually transmitted infections: Vaginitis and cervicitis: Pathology review
HIV and AIDS: Pathology review
Penile conditions: Pathology review
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Placenta previa p. 664
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Content Reviewers
Rishi Desai, MD, MPHContributors
Tanner Marshall, MS
Placenta previa means “placenta first,” because the placenta is the first thing within the uterine cavity.
In this condition, the placenta implants in the lower uterus, close to or even covering the uterine opening, called the internal cervical os, and it can therefore easily bleed, which usually happens after 20 weeks of gestation.
Normally the placenta implants in the upper uterus, and it's unclear why it implants in the lower uterus.
One hypothesis is that the placenta implants lower down when the endometrium in the upper uterus is not well vascularized.
In fact, endometrial damage from things like a previous cesarean section, an abortion (which could be induced or spontaneous), uterine surgery, and multiparity or multiple pregnancies can decrease vascularization and increase the risk of placenta previa.
In other cases, risk factors for placenta previa include having multiple placentas or a placenta with a larger than normal surface area, which can both happen with twins or triplets, as well as maternal age of 35 years or more, intrauterine fibroids, and maternal smoking.
Placenta previa is classified by how close the placenta is to the cervical os, it can be complete where the placenta completely covers the cervical os; partial where the placenta partially covers the cervical os; or marginal where the edge of the placenta extends to within 2 cm of the cervical os.
As the pregnancy progresses, the lower uterine segment grows, and if the placenta’s in the lower uterus, this growth disrupts the placental blood vessels, which can cause bleeding.
This usually a sudden onset of painless bright red bleeding that typically happens after 20 weeks gestation.
Summary
Placenta previa is a pregnancy complication in which the placenta implants in the lower uterus and partially or fully covers the internal cervical os, making vaginal delivery difficult or impossible. It can cause heavy vaginal bleeding and a serious threat to both the mother and the fetus. Symptoms include painless vaginal bleeding in the third trimester, and some risk factors are previous placenta previa, multiple gestation, and uterine fibroids.
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