Multifetal Gestation & Malpresentation Flashcards
(35 cards)
Etiology of dizygotic twins
2 separate ova are fertilized by 2 separate sperm
Distinct pregnancies coexisting in the same uterus — each will have its own amnion, chorion, and placenta
Etiology of monozygotic twins
Arise from cleavage of single fertilized ovum at various stages during embryogenesis
[arrangement of fetal membranes and placentas will depend on time at which embryo divides]
With monozygotic twins, the arrangement of fetal membranes and placentas will depend on time at which embryo divides.
Describe the nature of membranes when cleavage occurs during days 0-3
Dichorionic, diamnionic
Can be 2 separate placentas or one “fused”
With monozygotic twins, the arrangement of fetal membranes and placentas will depend on time at which embryo divides.
Describe the nature of membranes when cleavage occurs during days 4-8
Monochorionic, diamnionic
This is MOST COMMON type of placentation in monozygotic twins
With monozygotic twins, the arrangement of fetal membranes and placentas will depend on time at which embryo divides.
Describe the nature of membranes when cleavage occurs during days 9-12
Monochorionic, monoamnionic
This is MOST DANGEROUS type of placentation since there are not separating amnions — increases risk for cord entanglement and fetal demise
With monozygotic twins, the arrangement of fetal membranes and placentas will depend on time at which embryo divides.
Describe the nature of membranes when cleavage occurs after day 13
Conjoined twins (1 chorion, 1 amnion)
Types of conjoined twins
Craniopagus — joined at the cranium
Thoracopagus — joined at the chest wall [MOST COMMON]
Ischiopagus — joined by the coccyx and sacrum
Dizygotic twins are 2x more common than monozygotic. What factors increase the chances of having dizygotic twins?
Maternal age >35
Higher rates in caucasians and african american
What history/physical findings might lead you to suspect multiple gestations?
hCG higher than normal
Uterus palpates larger than dates
Auscultation of more than one FHR
Pregnancy has occurred after ovulation induction or IVF
Confirmation of multiples is by US — determines number of fetuses, gestational sacs, and chorionicity
Between monozygotic and dizygotic twins, which type has increased incidence of congenital anomalies, weight discordance, twin-twin transfusion syndrome, neurologic sequelae, premature delivery, and fetal demise?
Monozygotic twins
The most important step after diagnosing twins is determination of zygosity. How does ultrasonography help with determining zygosity?
In dizygotic — may see different fetal genders, visualization of thick amnion-chorion septum, “peak” or “inverted V” sign at base of septum
In monozygotic —dividing membrane is fairly thin
[if US is not definitive, inspect placenta after delivery, DNA analysis]
Twin Twin Transfusion Syndrome (TTTS) results secondary to uncompensated arterial-venous anastomoses in a monochorionic placenta, leading to net transfer of blood flow from one twin to the other. What are the associated fetal complications?
Donor twin — hypovolemia, hypotension, anemia, oligohydramnios, growth restriction
Recipient twin — hypervolemia, polyhydramnios, thrombosis, HTN, polycythemia, edema, cardiomegaly, CHF
BOTH twins are at risk of demise d/t heart failure
How is TTTS diagnosed?
Ultrasound
Donor twin will look smaller and show oligohydramnios, recipient twin will appear larger with polyhydramnios and possibly ascites
Treatment of TTTS
Serial amniocentesis with amniotic fluid reduction — can reduce preterm contractions secondary to uterine distention
More commonly used method now is laser photocoagulation of anastomosis vessels on the placenta
Complications of arterial to arterial anastomoses in monozygotic twins
Thrombosis within critical organs or atresias d/t trophoblastic embolization
The recipient twin is being perfused in a reverse direction with poorly oxygenated blood fails to develop normally — termed the ACARDIAC twin (has fully formed lower extremities but no anatomic structures cephalad of the abdomen)
Umbilical cord abnormalities are primarily associated with monozygotic monochorionic twins. What are some of these abnormalities?
Absence of umbilical a. (Often associated with other congenital anomalies like renal agenesis)
Velamentous umbilical cord insertion (may cause growth abnormalities)
Retained dead fetus syndrome may develop as a complication of monozygotic multiple gestation. What are the consequences of this based on week of gestation?
If gestation is 20+ weeks, retained dead fetus syndrome can develop DIC in the mother — must check platelets and fibrinogen levels weekly
If gestation is <12 weeks, the dead fetus is reabsorbed
If >12 weeks but <20 weeks, the fetus shrinks, dehydrates, and flattens, called the fetus papyraceus
General maternal complications with multiple gestations
Polyhydramnios Anemia Gestational HTN Preeclampsia Gestational DM Preterm labor C section delivery Postpartum hemorrhage Uterine atony
General fetal complications with multiple gestations
Prematurity Malpresentation Placenta previa Placental abruption PROM Umbilical cord prolapse IUGR Congenital anomalies Increased perinatal morbidity and mortality (RDS, intracranial hemorrhage, necrotizing enterocolitis)
Antepartum management of multiple gestation
Because high risk of preterm birth and preeclampsia, close antepartum surveillance is required.
First and second trimesters: 2 week office visits; US cervical length assessments
Third trimester: cervical length of <25mm at 24-28 wks increases risk of prematurity; serial US to check intrauterine growth (and for discordant growth), NSTs or weekly BPPs, bed rest
The majority of twin gestations deliver around 35-36 weeks and delivery by 38 weeks is recommended if pregnancy has no complications. When should monoamniotic twins be delivered and why?
32 weeks — secondary to increased risk for lethal cord entanglement
[Hospitalize at 26 weeks, antenatal steroids, and FHR monitoring several times daily]
Delivery of twins in vertex-vertex presentation
Managed similar to singleton vertex presentation labor
After delivery of first twin, cord is clamped and cut
Vaginal exam performed to assess presentation and station of second twin (second twin at more risk of cord prolapse, placental abruption, and malpresentation — so 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
Delivery of vertex-transverse and vertex-breech presentations in multiple gestation
Can be delivered vaginally but often are delivered by C section
[be aware that difficulty extracting breech twin can result in umbilical cord prolapse, head entrapment, neck injury, and asphyxia]
Delivery for breech-breech and breech-vertex twins in multiple gestations
C-section
