Placenta praevia
Encyclopedia
Placenta praevia is an obstetric
complication in which the placenta
is attached to the uterine
wall close to or covering the cervix
. It can sometimes occur in the later part of the first trimester, but usually during the second or third. It is a leading cause of antepartum haemorrhage
(vagina
l bleeding). It affects approximately 0.5% of all labours
.
Placenta praevia is hypothesized to be related to abnormal vascularisation
of the endometrium
caused by scarring or atrophy
from previous trauma, surgery, or infection.
In the last trimester of pregnancy the isthmus
of the uterus
unfolds and forms the lower segment. In a normal pregnancy the placenta does not overlie it, so there is no bleeding. If the placenta does overlie the lower segment, as is the case with placenta praevia, it may shear off and a small section may bleed.
may find the fetus in an oblique or breech position or lying transverse as a result of the abnormal position of the placenta. Praevia can be confirmed with an ultrasound
. In parts of the world where ultrasound is unavailable, it is not uncommon to confirm the diagnosis with an examination in the surgical theatre.
The proper timing of an examination in theatre is important. If the woman is not bleeding severely she can be managed non-operatively until the 36th week. By this time the baby's chance of survival is as good as at full term.
Placenta previa is classified according to the placement of the placenta:
Placenta previa is itself a risk factor of placenta accreta
.
There is debate as to whether vaginal delivery or delivery by Caesarean section is the safest method. In cases of fetal distress a Caesarean section is indicated. Caesarian section is contraindicated in cases of disseminated intravascular coagulation
.
A problem exists in places where a Caesarean section cannot be performed, due to the lack of a surgeon or equipment. In these cases the infant can be delivered vaginally. There are two ways of doing this with a placenta praevia:
The goal of this type of delivery is to save the mother, and both methods will often kill the baby. These methods were used for many years before Caesarean section and saved the lives of both mothers and babies with this condition.
The main risk with a vaginal delivery with a praevia is that as you are trying to bring down the head or a leg, you might separate more of the placenta and increase the bleeding.
Placenta praevia increases the risk of puerperal sepsis and postpartum haemorrhage because the lower segment to which the placenta was attached contracts less well post-delivery.
Obstetrics
Obstetrics is the medical specialty dealing with the care of all women's reproductive tracts and their children during pregnancy , childbirth and the postnatal period...
complication in which the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
is attached to the uterine
Uterine
The word uterine can refer to different meanings:* relating to or near the uterus or womb* having the same mother, but different fathers, see matrilineality...
wall close to or covering the cervix
Cervix
The cervix is the lower, narrow portion of the uterus where it joins with the top end of the vagina. It is cylindrical or conical in shape and protrudes through the upper anterior vaginal wall...
. It can sometimes occur in the later part of the first trimester, but usually during the second or third. It is a leading cause of antepartum haemorrhage
Antepartum haemorrhage
In obstetrics, antepartum haemorrhage , also prepartum hemorrhage, is bleeding from the vagina during pregnancy from the 24th , week gestational age to term....
(vagina
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
l bleeding). It affects approximately 0.5% of all labours
Childbirth
Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus...
.
Placenta praevia is hypothesized to be related to abnormal vascularisation
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
of the endometrium
Endometrium
-Function:The endometrium is the innermost glandular layer and functions as a lining for the uterus, preventing adhesions between the opposed walls of the myometrium, thereby maintaining the patency of the uterine cavity. During the menstrual cycle or estrous cycle, the endometrium grows to a...
caused by scarring or atrophy
Atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...
from previous trauma, surgery, or infection.
In the last trimester of pregnancy the isthmus
Uterine isthmus
The uterine isthmus is the inferior-posterior part of uterus, on its cervical end — here the uterine muscle is narrower and thinner. It connects superiorly-anteriorly to the complementary parts of the uterus: the body and the fundus....
of the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
unfolds and forms the lower segment. In a normal pregnancy the placenta does not overlie it, so there is no bleeding. If the placenta does overlie the lower segment, as is the case with placenta praevia, it may shear off and a small section may bleed.
Diagnosis
Women with placenta praevia often present with painless, bright red vaginal bleeding. This bleeding often starts mildly and may increase as the area of placental separation increases. Praevia should be suspected if there is bleeding after 24 weeks of gestation. Abdominal examination usually finds the uterus non-tender and relaxed. Leopold's ManeuversLeopold's maneuvers
In obstetrics, Leopold's Maneuvers are a common and systematic way to determine the position of a fetus inside the woman's uterus; they are named after the gynecologist Christian Gerhard Leopold. They are also used to estimate term fetal weight....
may find the fetus in an oblique or breech position or lying transverse as a result of the abnormal position of the placenta. Praevia can be confirmed with an ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
. In parts of the world where ultrasound is unavailable, it is not uncommon to confirm the diagnosis with an examination in the surgical theatre.
The proper timing of an examination in theatre is important. If the woman is not bleeding severely she can be managed non-operatively until the 36th week. By this time the baby's chance of survival is as good as at full term.
Placenta previa is classified according to the placement of the placenta:
- Type I or low lying: The placenta encroaches the lower segment of the uterus but does not infringe on the cervical osInternal orifice of the uterusThe internal orifice of the uterus is an interior narrowing of the uterine cavity. It corresponds to a slight constriction known as the isthmus that can be observed on the surface of the uterus about midway between the apex and base.-External links:...
. - Type II or marginal: The placenta touches, but does not cover, the top of the cervix.
- Type III or partial: The placenta partially covers the top of the cervix
- Type IV or complete: The placenta completely covers the top of the cervix
Incidence
Placenta previa occurs approximately one of every 250 births. One third of all antepartum hemorrhage occurs due to placenta previa.Risk factors
The following have been identified as risk factors for placenta praevia:- Previous placenta previa, caesarean deliveryCaesarean sectionA Caesarean section, is a surgical procedure in which one or more incisions are made through a mother's abdomen and uterus to deliver one or more babies, or, rarely, to remove a dead fetus...
, or D&CDilation and curettageDilation and curettage refers to the dilation of the cervix and surgical removal of part of the lining of the uterus and/or contents of the uterus by scraping and scooping . It is a diagnostic gynecological procedure.D&C normally is referred to a procedure involving a curette, also called sharp...
e.g. used for incomplete or missed miscarriageMiscarriageMiscarriage or spontaneous abortion is the spontaneous end of a pregnancy at a stage where the embryo or fetus is incapable of surviving independently, generally defined in humans at prior to 20 weeks of gestation...
, abortionAbortionAbortion is defined as the termination of pregnancy by the removal or expulsion from the uterus of a fetus or embryo prior to viability. An abortion can occur spontaneously, in which case it is usually called a miscarriage, or it can be purposely induced...
, to treat or investigate heavy bleeding or other diagnostic purposes. - Women who have had previous pregnancies, especially a large number of closely spaced pregnancies, are at higher risk.
- Women who are younger than 20 are at higher risk and women older than 30 are at increasing risk as they get older.
- Women with a large placentae from twinsTWINSTwo Wide-Angle Imaging Neutral-Atom Spectrometers are a pair of NASA instruments aboard two United States National Reconnaissance Office satellites in Molniya orbits. TWINS was designed to provide stereo images of the Earth's ring current. The first instrument, TWINS-1, was launched aboard USA-184...
or erythroblastosis are at higher risk. - Race is a controversial risk factor, with some studies finding that people from Asia and Africa are at higher risk and others finding no difference.
Placenta previa is itself a risk factor of placenta accreta
Placenta accreta
Placenta accreta is a severe obstetric complication involving an abnormally deep attachment of the placenta, through the endometrium and into the myometrium...
.
Intervention
An initial assessment to determine the status of the mother and fetus is required. Although mothers used to be treated in the hospital from the first bleeding episode until birth, it is now considered safe to treat placenta praevia on an outpatient basis if the fetus is at less than 30 weeks of gestation, and neither the mother nor the fetus are in distress. Immediate delivery of the fetus may be indicated if the fetus is mature or if the fetus or mother are in distress. Blood volume replacement (to maintain blood pressure) and blood plasma replacement (to maintain fibrinogen levels) may be necessary.There is debate as to whether vaginal delivery or delivery by Caesarean section is the safest method. In cases of fetal distress a Caesarean section is indicated. Caesarian section is contraindicated in cases of disseminated intravascular coagulation
Disseminated intravascular coagulation
Disseminated intravascular coagulation , also known as disseminated intravascular coagulopathy or consumptive coagulopathy, is a pathological activation of coagulation mechanisms that happens in response to a variety of diseases. DIC leads to the formation of small blood clots inside the blood...
.
A problem exists in places where a Caesarean section cannot be performed, due to the lack of a surgeon or equipment. In these cases the infant can be delivered vaginally. There are two ways of doing this with a placenta praevia:
- The baby's head can be brought down to the placental site (if necessary with Willet's forceps or a vulsellumVulsellumA vulsellum is a pair of surgical forceps with hooks at the tip of each blade. It is used in obstetrics and gynecology procedures....
) and a weight attached to his scalp - A leg can be brought down and the baby's buttocks used to compress the placental site
The goal of this type of delivery is to save the mother, and both methods will often kill the baby. These methods were used for many years before Caesarean section and saved the lives of both mothers and babies with this condition.
The main risk with a vaginal delivery with a praevia is that as you are trying to bring down the head or a leg, you might separate more of the placenta and increase the bleeding.
Placenta praevia increases the risk of puerperal sepsis and postpartum haemorrhage because the lower segment to which the placenta was attached contracts less well post-delivery.