antepartum hg Flashcards
Placenta previa def
The presence of placental tissue that extends over or lies proximate to the internal cervical os ( in the lower uterine segment ). Sequelae include the potential for severe bleeding and preterm birth, as well as the need for cesarean delivery.
- Incidence: 3.5-4.6 per 1000 births
Pathogenesis of placenta previa and pathophysiology
Pathogenesis :
The pathogenesis of placenta previa is unknown. One hypothesis is that the presence of areas of suboptimal endometrium in the upper uterine cavity due to previous surgery or pregnancies promotes implantation of trophoblast in, or unidirectional growth of trophoblast toward, the lower uterine cavity. Another hypothesis is that a particularly large placental surface area, as in multiple gestation or in response to reduced uteroplacental perfusion, increases the likelihood that the placenta will cover or encroach upon the cervical os.
Pathophysiology :
Placental bleeding is thought to occur when gradual changes in the cervix and lower uterine segment apply shearing forces to the inelastic placental attachment site, resulting in partial detachment. Vaginal examination or coitus can also disrupt the intervillous space and cause bleeding. Bleeding is primarily maternal, but fetal bleeding can occur if a fetal vessel is disrupted.
Major risk factors for placenta previa:
Previous placenta previa : Recurrence rate is 4-8%.
2) Previous cesarean delivery.
3) Multiple gestation.
4) Multi-parity.
5) Advanced maternal age.
6) Infertility treatment.
7) Previous abortion.
8) Previous intrauterine surgical procedure.
9) Maternal smoking.
10) Maternal cocaine use.
clinical presentation of placenta previa\talk about the hg
Clinical features: There are two presentations : 1-Antepartum hemorrhage. 2-Ultrasound presentation and course.
Antepartum hemorrhage :
In the second half of pregnancy, the characteristic clinical presentation is unprovoked painless vaginal bleeding, the blood is usually bright red and ranges in volume from scant to heavy, which occurs in 70-80 % of cases.
- An additional 10 -20 % of women present with both uterine contractions and
bleeding. Which is similar to the presentation of abruptio placenta.
In approximately one-third of affected pregnancies, the initial bleeding episode occurs prior to 30 weeks of gestation; this group is more likely to require blood transfusions and is at greater risk of preterm delivery and perinatal mortality than women whose bleeding begins later in gestation . An additional one-third of patients becomes symptomatic between 30 and 36 weeks, while most of the remaining patients have their first bleed after 36 weeks. About 10 % of women reach term without bleeding.
→ Digital vaginal examination is contraindicated in any woman beyond 20 weeks of gestation who presents with vaginal bleeding, until rule out of placenta previa by ultrasound.
→ Two theories have been put forth to account for resolution of the previa:
1)The lower uterine segment lengthens from 0.5 cm at 20 weeks of gestation to more than 5 cm at term. Development of the lower uterine segment relocates the stationary lower edge of the placenta away from the internal os.
2) Progressive unidirectional growth of trophoblastic tissue toward the fundus within
the relatively stationary uterus results in upward migration of the placenta. This
phenomenon has been termed trophotropism.
- If the previa persists with advancing gestational age, it is less likely to resolve.
Associated conditions: Placenta previa has been associated with an increased risk
of several other pregnancy complications
) Placenta accreta: Placenta accreta complicates 1-5 % of pregnancies with
placenta previa and an unscarred uterus.
Malpresentation : The large volume of placenta in the lower portion of the uterine cavity predisposes the fetus to assume a non-cephalic presentation.
Preterm labor and rupture of the membranes : Ante-partum bleeding from any cause is a risk factor for preterm labor and premature rupture of membranes.
Vasa previa and velamentous umbilical cord : they are uncommon, but when present they are often associated with placenta previa.
5) Congenital anomalies : Population-based cohort studies have reported an increase in the overall rate of neonatal congenital anomalies in pregnancies complicated by placenta previa, but no single anomaly or syndrome was associated with the disorder.
Diagnosis of placenta previa :
Diagnosis of placenta previa :
● Is based on identification of placental tissue covering or proximate to the internal
cervical os on an imaging study, typically ultrasound. (A distance greater than 2 cm
from the os excludes the diagnosis of previa).
Transabdominal U/S examination is performed as the initial examination; if it
shows placenta previa or the findings are uncertain, transvaginal U/S
(TVS) should be performed to better define placental position.
The overall false positive rate of transabdominal U/S for diagnosis of placenta
previa is high (up to 25 %), so the diagnosis should be confirmed by
TVS unless the previa is clearly central.
Superior performance of TVS over transabdominal U/S for diagnosis of
placenta previa. (provides a clearer image of the relationship of the edge
of the placenta to the internal cervical os)
. MRI is most
useful for diagnosis of complicated placenta previa, such as previa-accreta
and suspected posterior placenta previa.
Classifications of placenta previa :
Classifications of placenta previa :
The traditional classification of placenta previa describes the degree to which the placenta encroaches upon the cervix in labour ( opened cervix ) and is divided into :
Grade I ( low lying )(lateral): Placenta is in lower segment, but the lower edge does
not reach internal os
Grade II (marginal ): Lower edge of placenta reaches internal os,
but does not cover it.
- Grade III ( partial )( incomplete centralis): Placenta covers internal os partially.
Grade IV ( complete) (complete centralis) ( total ): Placenta covers internal os
completely
Minor placenta previa : Grade I and Grade II
Major placenta previa : Grade III and Grade IV
If the placental edge is more than 20 mm away from the internal os :
No Placenta Previa
- Post diagnostic evaluation :
Exclusion of placenta accreta : Using transvaginal ultrasound ± MRI.
Follow-up ultrasound examination : When the placenta previa was diagnosed in the second trimester, a follow up ultrasound examination for placental location in the third trimester is recommended ( between 32-36 weeks).
Management of placenta previa:
if
Asymptomatic placenta previa :
Asymptomatic placenta previa :
● Follow-up transvaginal ultrasound examination :
- For pregnancies >16 weeks :
- If the placental edge is ≥ 2 cm from the internal os, the placental location is
reported as normal and follow-up ultrasound for placental location is not
indicated.
- If the placental edge is < 2 cm from, or covering, the internal os : follow-up
ultrasonography for placental location is performed at 32 weeks of gestation.
- At 32 weeks follow up ultrasound :
- If the placental edge is ≥2 cm from the internal os, the placental location is
reported as normal and follow-up ultrasound for placental location is not
indicated. And these patients can be delivered vaginally safely. - If the placental edge is still <2 cm from the internal os or covering the cervical os,
1- Admission to hospital for observation till delivery. (? Outpatient )
2- Avoid sexual intercourse.
3- Single course of antenatal corticosteroid should be administered to
pregnancies at 26 to 35 weeks of gestation.
4- Follow-up TVS is performed at 36 weeks. if placenta previa persists,
schedule cesarean section at 37 weeks of gestation.
- If the placental edge is ≥2 cm from the internal os, the placental location is
Bleeding placenta previa :
management
Bleeding placenta previa :
initial interventions for women with bleeding placenta previa : (admission to labour room)
A) Stabilization of the mother :
I.V fluid - Secure intravenous access with at least one, and preferably two, wide-bore intravenous lines.
Closely monitor the mother’s hemodynamic status (heart rate, blood pressure, urine output). Urine output should be maintained at above 30 mL/hour and monitored with a Foley catheter.
Keep maternal oxygen saturation >95 percent and keep the patient warm.
Draw blood for a complete blood count, blood type and Rh ( preparation of 4 units PRBCs), and coagulation studies.
Call for help.
Notify the anesthesia team. Anesthesia-related issues in these patients include management of hemodynamic instability, technical issues related to bleeding diathesis, and the potential need for emergency cesarean delivery.
Notify the blood bank so blood replacement products (red blood cells, fresh frozen plasma, cryoprecipitate, platelets) will be readily available, if needed.
B) Immediately initiate continuous fetal monitoring.
● Severe bleeding and /or non reassuring FHR → Emergency cesarean
section.
- Anesthesia: General anesthesia is typically administered for emergency cesarean
delivery, especially in hemodynamically unstable women or if the fetal
status is nonreassuring. However, regional anesthesia is an acceptable
choice in hemodynamically stable women with reassuring fetal heart
rate tracings.
● Mild bleeding + Reassuring FHR + G.A < 37 weeks → Conservative
management.
Conservative management :
1- Symptomatic women often remain hospitalized from their initial bleeding
episode until delivery.
2- Correction of anemia.
3- 4 unites of PRBCs should be available.
4- Anti-D immune globulin for Rh(D)-negative women.
5- Schedule cesarean section at 37 weeks.
Delivery is indicated emergently if any of the following occur:
Delivery is indicated emergently if any of the following occur:
● Any vaginal bleeding with a non-reassuring fetal heart rate tracing
unresponsive to resuscitative measures.
● Life-threatening refractory maternal hemorrhage.
● Labor.
