LM 15.5: Abnormal Placentation

Question 1

what is placenta accretta spectrum?

Answer 1

aka morbidly adherent placenta

the hypothesis is that there is a failure of development of normal decidualizaiton due to a prior injury to the decidua basalis with development of a scar –> this leads to the Nitabuch’s layer not being formed or being abnormal

so chorionic villi attach to the myometrium rather than the decidua basalis –> they do not invade or penetrate the myometrium

this failure of normal decidualizaiton allows deep penetration of the trophoblast tissue

Question 2

what has been proposed as the leading cause for the increased prevalence of placenta accreta spectrum?

Answer 2

C-sections!!

they cause injury to the uterus which can lead to failure of development of normal decidualizaiton (decidua basalis)

Question 3

what are the risk factors for placenta accreta spectrum?

Answer 3

1. previous uteri surgery damaging basis and negatively effecting formation of Nitabuch’s
   ex. C-section, uterine myomectomy, D&C, endometrial ablation
2. placenta previa (associated with 80% of accretas!!)
3. abnormal biomarkers like increased maternal serum AFP
4. previous pelvic irradiation

Question 4

what is the spectrum of placenta accreta?

Answer 4

placenta accreta: superficial attachment to the myometrium; anchoring villi attach to the myometrium

placenta increta: chorionic villi penetrate into the myometrium

placenta percreta: chorionic villi penetrate through the myometrium to the uterine serosa or through the serosa and into adjacent organs

Question 5

why is placenta previa associated with such a high rate of placenta accreta?

Answer 5

uterine scar changes

placenta previa = a portion of the placenta covers the cervical os

Question 6

how do you diagnose placenta accreta?

Answer 6

1. US

2. MRI

Question 7

how is an US used to diagnose placenta accreta?

Answer 7

US findings will include:

1. loss of the normal hypo echoic zone between the placenta and myometrium
2. thin mometrial wall under the placenta
3. actual extension of placental tissue into surrounding layers or into nearby organs
4. turbulent lacunar flow demonstrated on color flow Doppler

absence of US findings does not exclude an accreta

Question 8

how is an MRI used to diagnose placenta accreta?

Answer 8

1. abnormal bulging of the placenta/uterus
2. disruption of the zone between uterus and placenta
3. abnormal or disorganized placental blood vessels
4. T2 weighted images with dark intra-placental bands

Question 9

what is the clinical presentation of accreta spectrum?

Answer 9

most commonly presents with bleeding due to association with previa

may be diagnosed prior to clinical presentation on an US due to evidence of myometrial invasion; US doesn’t always detect accreta disorder

diagnosis prior to delivery/hemorrhage is highly desired as these pregnancies need to be in a tertiary care center with mass transfusion and ICU capabilities

Question 10

what are the complications/outcomes associated with accreta spectrum disorder?

Answer 10

1. preterm birth

placental growth is abnormal and patient is at risk for antepartum bleeding

2. hemorrhage

abnormal placentation increases risk of hemorrhage; if with percreta then patient may even present with hemoperitoneum or hematuria

3. hysterectomy

if placenta is adherent to large areas and can’t be sheared from the uterine wall via normal uterine contraction then a hysterectomy is almost universally required…

Question 11

what is placenta previa?

Answer 11

the implantation of the placenta completely or partially over the internal loss of the cervix

if diagnosed in the 2nd trimester, there is the possibility that the placenta will move away from this position – this is probably the result of greater development of the upper uterine segment related to the lower uterine segment

Question 12

what is a low lying placenta?

Answer 12

when the edge of the placenta lay within 2 cm of the area around the os

Question 13

what are the risk factors for placenta previa?

Answer 13

1. previous uterine scar – prevents the placenta from “migrating” as it morbidly adheres to the scar
2. increasing maternal age
3. multifetal pregnancy
4. multiparity (especially 5+)
5. smoking
6. presence of leiomyomas
7. assisted reproductive technology
8. unexplained increase in maternal serum AFP

Question 14

what are the implications for the pregnancy if a patient has placenta previa?

Answer 14

if the placenta precedes the infant and gets delivered before the baby, maintenance of communication between the placenta and decimal interface is interrupted impacting fetal support/oxygenation

this is further complicated by the fact that this is occurring in the setting of maternal hemorrhage…

also, the placenta will detach from the uterine wall during cervical dilation exposing open vasculature of the implantation site leading to maternal bleeding all on its own! this can lead to hemorrhagic shock to both the mother and fetus

Question 15

what are the complications associated with placenta previa?

Answer 15

1. antepartum and/or postpartum hemorrhage
2. preterm birth
3. hysterectomy for postpartum hemorrhage control or co-existence of accreta spectrum disorder
4. accreta spectrum disorder
5. hemorrhage requiring transfusion or ICU time; hemorrhagic shock
6. DIC
7. intrauterine fetal death/neonatal death
8. acute kidney injury due to hypovolemic shock
9. Sheehan’s syndrome

Question 16

what is abruptio placenta?

Answer 16

aka placental abruption

it’s premature separation of the normally implanted placenta from the uterus before delivery of the fetus resulting in a retroplacental hematoma

thromboplastin can be pushed into maternal circulation leading to DIC

hematoma occurs in the decidua basalis so blood is maternal in origin

can be complete or partial separation; degree of sedation effects clinical significance –> can be silent or clinically evidence with vaginal bleeding

Question 17

what are the risk factors for developing abruptio placenta?

Answer 17

1. trauma
2. HTN
3. increasing maternal age
4. previous abruption
5. ethnicity (black and white women)
6. premature preterm rupture of membranes (PPROM)
7. smoking
8. cocaine
9. leiomyoma

Question 18

what is the clinical presentation of abruption placenta?

Answer 18

1. uterine pain/frequent painful contractions
2. vaginal bleeding
3. hemorrhage
4. non-reassuring fetal status on external fetal monitoring
5. intrauterine fetal death
6. maternal hemorrhagic shock

50% of abruptions are not detected with US!! a high index of suspicion has to be maintained for detection of abruption

Question 19

what is Sheehan’s syndrome?

Answer 19

pituitary failure after intrapartum or early postpartum hemorrhage of any etiology

Question 20

what is vasa previa?

Answer 20

umbilical cord vessels travel through membranes AND lie over the cervical os – so the umbilical veins and artery are not encased in Wharton’s jelly and are running over the os

this location leaves the vessels which contain fetal blood, vulnerable to laceration in the event of rupture of membranes which would results in fetal hemorrhage

Question 21

what are the risk factors for vasa previa?

Answer 21

1. bilobate or succenturiate placenta
2. placenta previa
3. velamentous cord insertion

Question 22

how do you diagnose vasa previa?

Answer 22

1. high index of suspicion with abnormal cord insertion, abnormal placental development and/or abnormal placental location
2. US and doppler

Question 23

what is a succenturiate lobe?

Answer 23

when a small lobe of the placenta is located away from the main placental disc

vessels course form the main disc to the lobe through the membranes

if the vessels are located over the os, this is a vasa previa and puts the fetus at risk for hemorrhage if the membranes rupture and tear through the vessels since the vessels are not protected by Wharton’s jelly….

Question 24

what are the 2 main placental tumors?

Answer 24

1. chorioangioma

2. metastatic tumors

Question 25

what is a placental chorioangioma?

Answer 25

primary tumor with blood vessels and stroma similar to chorionic villus

usually asymptomatic

if they’re large they can cause intraplacental arteriovenous shunting leading to high output cardiac failure to he fetus with resultant hydrops and death

trx: intrauterine laser ablation of the vascular supply of the tumor

Question 26

what is polyhydramnios?

Answer 26

presence of elevated amounts of amniotic fluid

amniotic fluid index (AFI) < 24 or deepest vertical pocket 8+ cm

higher incidence in multifetal gestations

the higher the degree of hydramnios, the higher the likelihood of anomaly or chromosomal abnormality

Question 27

what are the causes of polyhydramnios?

Answer 27

1. idiopathic (70% of cases)
2. increased fetal urine output (maternal DM resulting in fetal hyperglycemia)
3. impaired fetal swallowing (neuromuscular disorders)
4. obstruction or abnormality of fetal GI tract (esophageal fistula, cleft lip, micrognathia, etc.)
5. fetal hydrops
6. obstruction of trachea

Question 28

how do you diagnose polyhydramnios?

Answer 28

US

evaluate for:
1. amount of amniotic fluid

2. assess for maternal diabetes
3. evolution of fetal anatomy for congenital anomalies
4. consideration of amniocentesis for chromosomal abnormalities
5. evolution for fetal hydrops

Question 29

what are the consequences of polyhydramnios?

Answer 29

1. labor dysfunction
2. uterine atony
3. increased risk of cord prolapse if rupture of membranes occurs prior to engagement of presenting fetal part
4. abnormal fetal presentation (breech, etc.)

if severe, can actually result in such an enlarged uterus as to impact maternal respiratory function.

Question 30

what is oligohydramnios?

Answer 30

single deepest vertical pocket < 2cm on ultrasound

Question 31

what is the prognosis for early onset oligohydramnios?

Answer 31

generally poor prognosis as this often reflects a significant fetal or placental abnormality

rupture of membranes needs to be assessed

lack of adequate amniotic fluid early in gestation (less than ~ 20-22 weeks) can prevent normal development of the fetal lung leading to increased rates of pulmonary hypoplasia at birth if the pregnancy continues

renal anomalies/GU anomalies not uncommon with early oligohydramnios as by ~ 18 weeks, the kidneys are the main contributor to amniotic fluid volume

Question 32

what is associated with late onset oligohydramnios?

Answer 32

late 2nd or 3rd trimester oligohydramnios can be associated with the following:

1. intrauterine growth restriction
2. placental abnormality
3. maternal CVD, especially HTN
4. late term and post term pregnancy
5. rupture of membranes
6. ACE inhibitors taken in the 2nd or 3rd trimester resulting in fetal hypotension –> fetal renal hypo perfusion –> fetal renal ischemia –> anuric renal failure

Question 33

what is amniotic band syndrome?

Answer 33

associated with early rupture of membranes with continuation of pregnancy

leads to bands of amnion across the amniotic fluid that can attach to fetus or wrap around limbs which can result in craniofacial abnormalities or limb defects/amputations

Question 34

what is an amniotic fluid embolism?

Answer 34

amniotic fluid embolism with clinical onset during labor or within 30 minutes of delivering placenta with no fever and documentation of overt DIC

abrupt onset of cardiorespiratory arrest or both hypotension and respiratory compromise

it’s hypothesized that it’s due to fetal debris entering maternal circulation causing abnormal activation of proinflammatory mediator systems like SIRS – fetal lateral also contains tissue factor which activates widespread microthrombi and consumption of platelets and clotting factors (DIC)

Question 35

what is definied as an abnormal cord length?

Answer 35

greater than 100 or less than 30

both extremes are linked with fetal anomalies

too long = cord entangelemtn, cord prolapse

to short = abnormal fetal tracing

Question 36

what is an eccentric, marginal and velamentous insertion of the umbilical cord?

Answer 36

normal = central insertion

eccentric = not inserted in the middle but also not within the lateral 2 cm of placenta

marginal insertion = cord base inserted at edge of placenta

velamentous insertion = cord base is not located on the placenta; this leaves vessels to course through the membranes for that instance without protection of Wharton’s jelly