Clin: Multifetal Gestation and Malpresentation - Moulton Flashcards
two separate ova are fertilized by two separate sperm
- are distinct pregnancies coexisting in the same uterus
- each will have it’s own amnion, chorion and placenta
fraternal (dizygotic) twins
arise from the cleavage of a single fertilized ovum at various stages during embryogenesis
- arrangement of fetal membranes and placentas will depend on the time at which the embryo divides
identical (monozygotic) twins
how many chorions, how many amnions for dichorionic diamniotic monozygotic placentation?
2 placenta
2 amnions
- cleavage at days 0-3
- can be two separate placentas or one fused
- 30% on monozygotic twins have this presentation
how many chorion, how many amnions for monochorionic diamniotic monozygotic placentation?
1 placenta
2 amnions
- cleavage at days 4-8
69% of monozygotic twins have this presentation
how many chorion, how many amnion for monochorionic monoamniotic monozygotic placentation?
1 placenta
1 amnion
- cleavage days 9-12
- 1% on monozygotic twins have this placentation
- is the most dangerous since there are not separating amnions
- cord entanglement risk if high
- net mortality in these twins is 50-80%
what is a craniopagus?
twins joined at the cranium
- 2% incidence
what is a thoracopagus?
twins joined at the chest wall
- 30-40% incidence
what is an ischiopagus?
twins joined by the coccyx and sacrum
- 6% incidence
what is the frequency of monozygotic twins?
constant among all populations at 1 in 250 births
- 1/3 of spontaneous twins are monozygotic
what are the influences of dizygotic twins?
- maternal age: 2x more common after 35 y/o
- family hx and ethnicity: lower among asians, Western nigerian tribe has dizygotic twinning occurance of 1 in 22 gestations
- 2/3 of spontaneous twins are dizygotic
when would you suspect multiple gestations?
- hCG higher than normal
- uterus palpates larger than dates
- auscultation of more than 1 fetal HR
- pregnancy has occurred after ovulation induction or IVF
prognosis and expected morbidity of twins is strongly dependent on what?
zygosity
- is the most important step after diagnosing twins!
monozygotic twins have increased incidence of what?
- congenital anomalies
- weight discordancy
- twin-twin transfusion syndrome (TTTS)
- neorologic squeale
- premature delivery
- fetal demise
US to determine zygosity:
- different fetal gender
- visualization of a thick amnoin-chorion septum
- “peak” or “inverted V” sign at the base of the septum
dizygotic
US to determine zygosity
- dividing membrane is fairly thin
monozygotic
what if US is not definitive in determining zygosity?
- inspect placenta after delivery
- DNA analysis
- cleavage occurs 13-15 days
- 1 in 70,000 deliveries
- mortality rates 50%
- c-section delivery
- advancement of imaging allows mapping of shared organs and more successful surgical separation procedures
- elective termination if cardiac or cerebral fusion is identified
conjoined twins
- 90% occur in monochorionic twins
- most common type is arterial-arterial followed by arterial-venous and then venous-venous
- vascular communications between 2 fetuses through the placenta can cause problems (abortion, polyhydramnios, TTTS, fetal malformation)
interplacental vascular anastomoses
results secondary to uncompensated arterial-venous anastomoses in a monochorionic placenta
- leads to a net transfer of blood flow going from 1 twin to other
twin-twin transfusion syndrome (TTTS)
what are the fetal complications of TTTS?
- donor twin
- recipient twin
- donor twin: hypovolemia, hypotension, anemia, oligohydramnios, growth restriction
- recipient twin: hypervolemia, polyhydramnios, thrombosis, HTN, polycythemia, edema, cardiomegaly, CHF
what are both twins at risk for in TTTS?
heart failure -> demise
can you diagnose TTTS on US?
yes!
- donor twin: smaller, “stuck” appearance, oligohydramnios
- recipient twin: larger, polyhydramnios, ascites
what is the tx of TTTS?
- serial amniocentesis with amniotic fluid reduction (can reduce preterm contractions secondary to uterine distention)
- laser photocoagulation of the anastamotic vessels on the placenta (performed at specialized centers)
- arterial blood flow from the donor twin enters the arterial circulation of the recipient twin
- reversed blood flow may cause thrombosis within critical organs or atresias due to trophoblastic embolization
- the recipient twin, being perfused in reverse direction with poorly oxygenated blood fails to develop normally -> known as ACARDIAC twin (fully formed lower extremities, no amatomic structures cephalad of the abdomen)
abnormalities in monozygotic twins with arterial to arterial anastomoses
this abnormality is primarily associated with monochorionic twins
- absence of umbilical artery
- occurs in 3-4% of twins (1% in singletons)
- velamentous umbilical cord insertions occur more frequently (may cause growth abnormalities)
umbilical cord abnormalities in monozygotic twins
what is vanishing twin syndrome?
when <12 weeks, the dead fetus is reabsorbed
what is retained dead fetus syndrome
if gestation >20 weeks
- disseminated intravascular coagulopathy in the mother
- single fetal death in utero
- check platelets and fibrinogen levels weekly
what is fetus papyraceus?
if >12 weeks, the fetus shrinks, dehydrates and flattens
- polyhydramnios
- anemia
- gestational HTN
- preeeclampsia
- GDM
- preterm labor
- c-section
- postpartum hemorrhage
- uterine atony
maternal complications of multiple gestations
- prematurity
- malpresentation
- placenta previa
- placental abruption
- PROM
- umbilical cord prolapse
- IUGR
- congenital anomalies
- increased perinatal morbidity/mortality (RDS, intracranial hemorrhage, necrotizing entercolitis)
fetal complications of multiple gestations
what is the antepartum management of multiples in first and second trimesters?
- 2 week office visits
- US cervical length assessments
what is the antepartum management of multiples in the third trimester?
- serial US to check intrauterine growth q 4-6 weeks, begin at 24 weeks
- antepartum test (NST weekly, or BPP)
- pt often placed on bed rest
what are you looking for in serial US during third trimester?
looking for discordant fetal growth
- defined by 20% reduction in fetal weight of the smallest fetus compared with the largest
when should monoamniotic twins be delivered?
by 32 weeks
- secondary to increased risk of lethal cord entaglement
- hospitalization at 26 weeks, antenatal steroids, and fetal heart monitoring several times daily
when do the majority of twin gestations deliver?
35-36 weeks
- recommend delivering at 38 weeks if pregnancy has no complications
what are the prerequisites for intrapartum management of twins?
- large bore IV
- simultaneous fetal HR monitors
- anesthesiologist
- US to determine presentation
- two pediatricians/NICU personnel, one for each baby
after delivery of first twin, cord is clamped and cut
- vaginal exam is performed to assess presentation and station of second twin
- second twin at increased risk of cord prolapse, placental abruption and malpresentation
- pay close attention to fetal monitoring!
- after second twin delivers, obtain cord samples and deliver placenta
- be prepared for postpartum hemorrhage secondary to uterine atony
vertex-vertex presentation
- can manage similar to singleton
difficulty extracting a breech second twin can result in what?
- umbilical cord prolapse
- head entrapment
- neck injury
- asphyxia
how are breech-breech and breech-vertex twins delivered?
c-section
NOTE: vertex-transverse and vertex-breech can be delivered vaginally
why is there a 5x greater perinatal mortality in twins?
- secondary to prematurity and congenital anomalies
- RDS and intracranial hemorrhage
- birth asphyxia: second twins have 2x more perinatal mortality than the first born twin, 4x more likely than first to die from birth trauma complications
4 fold increase in what is noted in twins?
cerebral palsy
- stillbirths occur 2x more frequently than singletons
what are the most likely causes of higher order multiples?
embryo splitting and polyovulation
- most frequently result of ovulation induction agents
- triplets 1 in 3,000 with ART, spontaneous = 1 in 8,000
- spontaneous quads 1 in 700,000
what are the average gestation ages at delivery of triplets and quads?
triplets: 33 weeks
quads: 29 weeks
- by c-section
what are the factors associated with breech presentation?
- prematurity (before 28wks, 24% of fetuses are breech)
- fetal malformations: hydrocephaly, anencephaly
- multiple pregnancies
- uterine malformations: bicornate uterus
how to you dx a breech presentation?
leopolds maneuver, US and pelvic exam
most common breech presentation
- thighs are flexed
- lower extremities are extended at knees
Frank presentation (65%)
thighs are flexed
- lower extremities are flexed (sitting cris-cross)
complete (25%)
1 or both thighs are extended
- 1 or both feet are below the buttocks
incomplete (10%)
applying pressure to the mother’s abdomen to turn the fetus in either a forward or backward somersault to achieve a vertex position
external cephalic version (ECV)
- candidates: 36 weeks, NOT in labor
what are the contraindications for ECV?
- placenta previa
- non-reassuring fetal monitoring
- oligohydramnios
- previous uterine surgery that is a contraindication for vaginal delivery
- pt should be NPO x 7 hrs
- IV access
- performed in hospital that is equipped for immediate c-section if necessary
- place on continuous monitoring (NST or BPP)
- consider tocolytics (nulliparous) or anesthesia
ECV
- successful 58% of the time
what are the criteria for vaginal delivery of breech presentation?
- fetus must be in frank or complete presentation
- > 37 weeks
- fetal weight 2500-4000g
- fetal head must be flexed
- adequate maternal pelvis
- no maternal or fetal contraindications for vaginal delivery
- assistant and anesthesia prepared to assist
what is the standard of care now regarding breech deliveries?
most practices, is to deliver all breeches by c-section
assisted breech vaginal delivery
- premature aggressive traction can cause what?
deflexion of the fetal vertex and increase risk of head entrapment or nuchal arm entrapment
- allow fetus to deliver scapulae
what do you do after spontaneous expulsion of the scapulae in an assisted breech vaginal delivery?
external rotation of each thigh combined with opposite rotation of the fetal pelvis results in flexion of the knee and delivery of the leg
when the scapulae appears under the symphysis, what do you do in an assisted breech vaginal delivery?
wrap a towel around the fetus for better traction
- reach over the left shoulder, sweep the arm across the chest and deliver the arm
- delivery of the head is easily accomplished with continued uterine contractions, suprapubic pressure and gentle traction
to deliver the head in an assisted breech vaginal delivery, maintain cephalic flexion by applying pressure where?
the fetal maxilla NOT mandible
what kind of forceps can be used in breech deliveries?
piper forceps
in a breech presentation, the head can become entrapped, leading to what?
fetal asphyxia with increased morbidity/mortality
NOTE: perinatal mortality for breeches is higher than for vertex fetuses
what are the most common factors for perinatal mortality of breech presentations?
lethal congenital anomalies, prematurity (most common) birth trauma, asphyxia
this presentation occurs when the presenting part of the fetus is between the facial orbits and anterior fontanelle
- head is extended backwards (not flexed)
- presenting diameter is the supraoccipitomental diameter (13.5cm compared to 9.5 for suboccipitobregmatic)
- frontal bones are the point of designation
- incidence: 1 in 1,400
BROW presentation
- 50-75% will convert to a face presentation (through extension) or a vertex presentation (through flexion) and then deliver
NOTE: persistent brow presentation makes vaginal delivery impossible -> deliver by c-section
this presentation is characterized by full extension of the fetal head and neck with occiput against upper back
- incidence in 1 in 500 deliveries
- anencephaly seen in 1/3 of these presentations
- fetal chin is chosen as point of designation
FACE presentation
which face presentation can be delivered vaginally?
which MUST be done via c-section?
- mentum anterior: 60% can deliver vaginally
- mentum posterior can NOT deliver vaginally
trachelobregmatic diameter
head is completely extended backwards
- 12.6cm diameter
this presentation is when a fetal extremity (usually the hand) is found prolapsed alongside the presenting fetal part (head)
- occurs more frequently with premature gestation
- incidence of fetal arm or hand prolapsing along side the presenting head occurs 1 out of every 700 deliveries
COMPOUND presentation
- may resolve on its own as it comes down the pelvis
- some recommend gently pushing the small part upward while simultaneously applying fundal pressure
- c-section if failure progresses, cord prolapse, or non-reassuring fetal status noted
what does cervical length <25mm at 24-48 weeks double the risk of?
preterm birth
