Multifetal Gestations Flashcards
Dizygotic (fraternal) twins
Two separate ova are fertilized by two separate sperm.
They are distinct pregnancies coexisting in the same uterus (each has its own amnion, chorion and placenta).
Monozygotic (identical) twins
A single fertilized ovum is cleaved at various stages during embryogenesis, therefore the arrangement of fetal membranes and placentas depends on which time the embryo divides.
How many chorions/amnions exist in monozygotic twins if cleavage occurs at 0-3 days?
How many twins have this placentation?
2 chorions and 2 amnions
30%
How many chorions/amnions exist in monozygotic twins if cleavage occurs at 4-8 days?
How many twins have this placentation?
1 chorion and 2 amnions
60%
How many chorions/amnions exist in monozygotic twins if cleavage occurs at 9-12 days?
How many twins have this placentation?
1 chorion and 1 amnion
1%
Which placentation is the most dangerous? Why?
What is at a high risk?
What is the net mortailty?
Monochorionic monoamniotic (9-12 days of cleavage) due to lack of separating amnions.
Cord entanglement
50-80% mortality
How many chorions/amnions exist in monozygotic twins if cleavage occurs at 13-15 days?
What is craniopagus vs. thoracopagus vs. ischiopagus? What are their incidences in this placentation category?
1 chorion and 1 amnion.
Craniopagus: joined at the cranium - 2%
Thoracopagus: joined at chest wall - 30-40%
Ischiopagus: joined at coccyx and sacrum - 6%
What percent of spontaneous twins are monozygotic twins vs. dizygotic twins?
Monozygotic: 1/3
Dizygotic: 2/3
What influences the development of dizygotic twins?
Maternal age: 2x more common in women >35 y/o
Family history and ethnicity (Asian
How is confirmation of multiple gestation made?
US
Which twin type is most likely to cause problems in pregnancy?
Monozygotic
What features suggest dizygosity on US? (3)
Different gender
Thick amnion-chorion septum
“Peak” or “inverted V” signat base of the septum
What feature suggests monozygosity on US?
The dividing membrane is fairly thin
If US is not definitive of zygosity, what should be done to determine it?
Placental inspection post delivery
DNA analysis
Interplacental vascular anastomoses occur in which twins? How commonly?
What is the most common type?
What complications can ensue?
90% of monochorionic twins
Arterial-arterial type
Aboriton, polyhydramnios, TTS, fetal malformations, etc.
What is TTTS?
What are the risks for each twin?
What is the prognosis?
Twin-twin transfusion syndrome - there is a net transfer of blood flow from one twin to another.
Donor twin: hypovolemia, hypotension, anemia, oligohydramnios, growth restriction
Recipient twin: hypervolemia, polyhydramnios, thrombosis, HTN, polycythemia, edema, cardiomegaly, CHF
Poor - both twins are at risk due to HF. If untreated, mortality is high.
What is the treatment of TTTS?
Serial amniocentesis with amniotic fluid reduction.
-can reduce preterm contraction secondary to uterine distention (polyhydramnios) and maternal symptoms
Laser photocoagulation of anastomosing vessels on the placenta is done at specialized centers.
What happens in arterial to arterial anastomoses in twins?
What is the “acardiac twin”?
Arterial blood flow from the donor twin enters the arterial circulation of the recipient twin. The reversed blood flow may cause thromboses within critical organs or atresia due to trophoblastic embolization.
The recipient twin, being perfused in a reverse manner with poorly oxygen blood, fails to develop normally.
- fully formed lower extremities
- no anatomic structures above the abdomen
Umbilical cord abnormalities are primarily associated with…
What structure is absent? What are they associated with?
Which cord abnormality is most common?
Monochorionic twins (monozygotic)
Absence of umbilical a. -> 30% associated with other congenital anomalies
Velamentous umbilical cord insertions
Retained dead fetus syndrome is associated with which twin type?
What can develop if gestation is >20 wks with a retained dead fetus?
What happens if there is a retained dead fetus < 12 wks?
What if there is a retained dead fetus > 12 wks?
Monozygotic twins
> 20 wks: DIC in the mom (check platelets and fibrinogen weekly)
< 12 wks: reabsorbed - “Vanishing twin syndrome”
> 12 wks: the fetus shrinks, dehydrates and flattens - fetus papyraceus
What is the antepartum management of twins in the first and second trimesters? (2)
Third trimester? (3)
1st and 2nd: 2 week office visits, US cervical length measurements.
Serial US to check for intrauterine growth q4-6 wks beginning at 24 wks.
-check for discordant fetal growth (20% less fetal weight in smaller fetus)
NSTs or weekly BPPs
Possible bed rest
A cervical length at which time doubles the risk for premature birth in twins?
25 mm at 24-28 wks
When should monoamniotic twins be delivered generally? Can it ever be delayed?
When does hospitalization begin? What is done at that time? (2)
When do most twins deliver? What is the OBGYNs preference?
At 32 wks (secondary to lethal cord entanglement)
Hospitalize at 26 wks and given antenatal steroids and FHR monitoring several times daily.
Most deliver at 35-36 wks, but the preference is to deliver at 38 wks.
What can be done for intrapartum management of twins? (7)
Delivery room equipped for emergent C-section
Large IV bore needle, blood products
FHR monitoring
Anesthesiologist available
US to determine precise presentations of twins
2 peds/NICU personnel (1 per baby)
Appropriate number of nurses
What is the vertex-vertex positioning of twins?
Head first in both babies.
Delivery as you would a single vertex baby, then cut cord and do a quick vaginal exam.
Which twin positions can be delivered vaginally, but are most commonly delivered via C-section?
Vertex-transverse and vertex-breech
Which twin positions are delivered only via C-section?
Breech-breech and breech-vertex
What are some possible causes of mortality in twins? (3)
Prematurity and congenital anomalies
RDS and intracranial hemorrhage
Birth asphyxia - second twin is at a 2x greater risk
Breech presentation is…
What factors are associated with it? (4)
How can it be diagnosed? (3)
Fetal butt or LE presents to the maternal pelvis (4% of deliveries)
Prematurity, fetal malformations (hydrocephaly and anencephaly), multiple pregnancies, uterine malformations
Leopold’s maneuver, US and pelvic exam
What are the 3 subtypes of the breech position? Which is most common?
Frank (65%) - thighs flexed, LE are extended at the knees
Complete (25%) - thighs are flexed and LE are flexed at the knees
Incomplete (10%) - 1 or both thighs are extended and 1 or both are below the butt
What is external cephalic version (ECV)?
Which patients are candidates?
Applied pressure to the mother’s abdomen to turn the fetus in a forward or backward somersault to achieve vertex positioning.
36 wks gestation and not in labor.
What is the standard of care for delivery of breech positioned babies?
C-section
In premature breeches, what is the major concern?
The head is enlrgaed (usually) so the concern is that is might be trapped and lead to asphyxia.
What is the brow presentation?
What is the presenting diameter?
What is the point of desigation?
The brow position may convert to what? (2)
What is the preferred delivery if the brow position remains?
The presenting part of the fetus is between the facial orbits and anterior fontanelle.
Supraoccipitomental diameter.
Frontal bones.
50-75% will extend and convert to face presentation or flex to a vertex presentation and then deliver.
C-section
What is the face position?
What is it often associated with?
What is the point of designation?
How can the mentum present and what route of delivery is preferred?
Full extension of the fetal head and neck with occiput against upper back.
Fetal malformations (anencephaly seen in 1/3 of these presentations)
Fetal chin is point of designation.
60% present mentum anterior and deliver vaginally.
If mentum posterior, C-section must be done.
What is a compound presentation?
When does it occur most often?
How is it managed?
A fetal extremity (usually hand) is prolapsed alongside the presenting fetal part (head).
More common in premature gestation.
May resolve on its own as baby descends down the pelvis. If it does not, a C-section is indicated.
Which forceps are used in breech deliveries?
Piper forceps
