placenta previa Flashcards
Definition
Placenta previa is a placenta implanted in the lower uterine segment in the
zone of effacement and dilation of the cervix, so that it lies alongside or in front of
the presenting part and obstructs its descent.
Frequency
● Encountered in approximately 1/200 births (0.8/of pregnancies)
● 90% of sick patients are multiparous
● 20% of cases are complete type
Classification
i) Low lying placenta – placenta lies ,7cm from internal cervical os.
ii) Marginal placenta previa – lies at rim of internal os but does not close it
iii) Partial placenta previa (incomplete) – covers part of internal os when dialted and fully when closed.
iv) Complete placenta previa (central) – close the internal os completely even when fully dilated
Etiology
i) In multiple gestation, the large size of the placent and its surface area results in
the implantation of at least a part in the lower segment.
ii) In previous low CS scars – previous endometrial damage and poor vascularisation.
iii) In multiparous, rapid embryo transport and arrival at uterine cavity before
endometrim is receptive.
iv) In old age – decreased invasive power of trophoblast
Risk factors
- Predisposed women:
● advanced age
● multiparity
● previous low CS (increase incident by 3x)
● Multiple pregnancy 🡪 large placenta (2x more common)
● History of PP
Clinics
- As the lower segment is formed by the stretching 🡪 placenta separates and leak of blood from maternal sinuses. Therefore, main sign of PP 🡪 “Painless Hemorrhage”
● I + II + TM - spotting
● III TM – sudden, painless, profuse bleeding usually after 28th week. Usually,
120ml. Blood is birght and bleeding is painless because blod is not retained in
uterine cavity. In 10% 🡪 spontaneous labor within few days.
● Uterus is soft, relaxed, non tender
● Due to pushing of presenting part upwards by PP 🡪 malpresentation (oblique,
transverse/breech)
● General condition of patient depends on amount of blood lost. If 500ml or more is lost🡪 peripheral vasoconstriction.
🡪pallor/↑ HR in severe cases 🡪 hypovolumic shock (maternal CVS
compromise)
Diagnosis
i) Clinical signs
ii) US examination to detect level of placenta
iii) Thermography, Radiography, radioisotope investigations not used in modern days.
iv) Abdominal examination 🡪 Uterus os soft/relaxed but also malpresentaiton is
common. Also maybe:-
b) deviation of presenting part from midline 🡪 Lateral AP
c) Difficulty in palpating presenting part 🡪 Ant PP
d) Under prominence of presenting part 🡪 Post PP
v) Digital examination – only done when delivery is intended under anaesthesia in a
room prepared for CS vaginal fornices are carefully palpated to feel for placenta
and if not felt 🡪 finger is passed through cervis to explore lower segment. Also
done to determine if head can pass through birth canal.
Differential Diagnosis
a) placenta abruption – in this case blood is dark, bleeding is continuous and
occurs at onset of labor. Uterus is tense, tender and
painful. If shock sets in, it is disproportional to amount
of bleeding seen. Fetus is usually dead and no
malpresentation.
b) Cervical pregnancy – implantation in cervix 🡪 rare and ends in abortion.
c) Marginal hemorrhage(like accumulate placenta). Bleeding is brown.dark
red and is persistent.
d) Vasa previa - bleeding from fetal vessels 🡪 when membrane ruptures 🡪
small blood loss.
Complications
i) Maternal:
a) Antepartum, Intrapartum, postpartum (due to inefficient compression of
vessels by the lower muscle).
Hemorrhage 🡪 hypovolumic shock 🡪 shock
b) Embolism through lower blood sinuses
c) Operative trauma to lower uterine segment and in general associated with
CS, anaesthesia
d) Infections (ascending and sepsis)
ii) Fetal:
a) Prematurity , 36 ,weeks – 60% of fetal deaths
b) Intrauterine
c) Malpresentation 🡪 birth trauma
d) Risks associated with CS, anesthesia
e) Congenital malformations, umbilical cord prolapse/compression in
vaginal delivery.
