History and exam

Key diagnostic factors

common

scarred uterus

Uterine scarring, usually secondary to a previous cesarean section, is a common finding.[37][44]

presence of other risk factors

Additional risk factors include advanced maternal age, smoking, previous multiple pregnancies/short inter-pregnancy intervals or miscarriages/induced abortions, prior PP, infertility treatment, and illicit drug use.

painless vaginal bleeding

Symptomatic PP typically presents as second- or third-trimester vaginal bleeding.[37][44][45]

Bleeding may range in severity, from light, moderate, heavy, to massive.

Digital vaginal examination should not be performed on women with active vaginal bleeding until the position of the placenta is known with certainty.[43]

absence of cervical/vaginal causes of bleeding on speculum examination

Very careful speculum examination may be used to exclude cervical or vaginal hemorrhage as a cause of bleeding in women in early labor with mild bleeding.

This should be done under "double setup" to allow conversion to an immediate cesarean section in case of massive vaginal bleeding.

Digital vaginal examination should never be performed before PP is ruled out by other means.[43]

Other diagnostic factors

common

previous ultrasound anomaly in first trimester

Most occurrences of low-lying placenta found incidentally on ultrasound will resolve spontaneously as pregnancy progresses. Nevertheless, this remains an important risk factor for persistent previa.[48]

lack of uterine tenderness

Most women with placenta previa and bleeding will have nontender uterus on physical examination.

Tenderness may be present if there is coexisting placental abruption or labor.

low blood pressure and tachycardia

Hypotension and tachycardia may indicate reduced blood volume secondary to hemorrhage.

However, in assessing the hemodynamic effects of bleeding it is important to remember that most young, otherwise healthy pregnant women tend to have slightly low blood pressure and to be slightly tachycardic.

Risk factors

strong

uterine scarring (most commonly due to prior cesarean section)

In the US, the frequency of placenta previa has been increasing secondary to the increase in the use of cesarean sections. One cesarean section increases the incidence in the next pregnancy to about 0.6%.[6] Subsequent cesarean sections increase the risk slightly compared with one procedure.[6][9][11]

Although the association is weak, it is strong enough to justify a midtrimester ultrasound to determine placental location.[6][9][10][11][24]

infertility treatments

Pregnancies resulting from IVF have about a 2% risk of placenta previa.[30][31][32][33][34][35] Although the association is weak, it is strong enough to justify a midtrimester ultrasound to determine placental location.

prior placenta previa

Placenta previa has a very slight risk of recurrence (about 0.7%).[13]

weak

advanced maternal age

Association with advanced maternal age is increasingly recognized.[12][16][17][18][19]

multiple previous pregnancies

Association with multiparity has been reported.[13][20]

smoking

Association with smoking has been reported.[13][14][21]

previous miscarriage

Association with previous miscarriage and recurrent pregnancy loss has been reported.[22][23]

previous induced abortion

Association with previous abortions has been reported.[24][25]

other placental abnormalities

Association with other placental abnormalities has been reported. These include the following:

Velamentous insertion (where the umbilical cord inserts upon the chorioamniotic fetal membranes instead of the placental mass)[26]

Succenturiate placenta (where the placenta has one or more accessory lobes).[27]

short interpregnancy intervals

Association with shortened birth spacing has been reported.[28]

illicit drug use

A history of maternal cocaine use, independent of tobacco use, is associated with an increased risk for placenta previa.[29]

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