Multifetal Gestation & Malpresentation

Question 1

Etiology of dizygotic twins

Answer 1

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

Question 2

Etiology of monozygotic twins

Answer 2

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]

Question 3

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

Answer 3

Dichorionic, diamnionic

Can be 2 separate placentas or one “fused”

Question 4

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

Answer 4

Monochorionic, diamnionic

This is MOST COMMON type of placentation in monozygotic twins

Question 5

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

Answer 5

Monochorionic, monoamnionic

This is MOST DANGEROUS type of placentation since there are not separating amnions — increases risk for cord entanglement and fetal demise

Question 6

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

Answer 6

Conjoined twins (1 chorion, 1 amnion)

Question 7

Types of conjoined twins

Answer 7

Craniopagus — joined at the cranium

Thoracopagus — joined at the chest wall [MOST COMMON]

Ischiopagus — joined by the coccyx and sacrum

Question 8

Dizygotic twins are 2x more common than monozygotic. What factors increase the chances of having dizygotic twins?

Answer 8

Maternal age >35

Higher rates in caucasians and african american

Question 9

What history/physical findings might lead you to suspect multiple gestations?

Answer 9

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

Question 10

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?

Answer 10

Monozygotic twins

Question 11

The most important step after diagnosing twins is determination of zygosity. How does ultrasonography help with determining zygosity?

Answer 11

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]

Question 12

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?

Answer 12

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

Question 13

How is TTTS diagnosed?

Answer 13

Ultrasound

Donor twin will look smaller and show oligohydramnios, recipient twin will appear larger with polyhydramnios and possibly ascites

Question 14

Treatment of TTTS

Answer 14

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

Question 15

Complications of arterial to arterial anastomoses in monozygotic twins

Answer 15

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)

Question 16

Umbilical cord abnormalities are primarily associated with monozygotic monochorionic twins. What are some of these abnormalities?

Answer 16

Absence of umbilical a. (Often associated with other congenital anomalies like renal agenesis)

Velamentous umbilical cord insertion (may cause growth abnormalities)

Question 17

Retained dead fetus syndrome may develop as a complication of monozygotic multiple gestation. What are the consequences of this based on week of gestation?

Answer 17

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

Question 18

General maternal complications with multiple gestations

Answer 18

Polyhydramnios
Anemia
Gestational HTN
Preeclampsia
Gestational DM
Preterm labor
C section delivery
Postpartum hemorrhage
Uterine atony

Question 19

General fetal complications with multiple gestations

Answer 19

Prematurity
Malpresentation
Placenta previa
Placental abruption
PROM
Umbilical cord prolapse
IUGR
Congenital anomalies
Increased perinatal morbidity and mortality (RDS, intracranial hemorrhage, necrotizing enterocolitis)

Question 20

Antepartum management of multiple gestation

Answer 20

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

Question 21

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?

Answer 21

32 weeks — secondary to increased risk for lethal cord entanglement

[Hospitalize at 26 weeks, antenatal steroids, and FHR monitoring several times daily]

Question 22

Delivery of twins in vertex-vertex presentation

Answer 22

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

Question 23

Delivery of vertex-transverse and vertex-breech presentations in multiple gestation

Answer 23

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]

Question 24

Delivery for breech-breech and breech-vertex twins in multiple gestations

Answer 24

C-section

Question 25

T/F: risk of prematurity increases as number of fetus’ increases

Answer 25

True

Triplets avg gestation at delivery is 33 wks, quadruplets at 29 wks

[note: must deliver via C section]

Question 26

Breech presentation may be diagnosed by Leopolds maneuver, US, and/or pelvic exam. What are some factors associated with breech presentation

Answer 26

Prematurity (most common factor associated with breech)

Fetal malformations (hydrocephaly, anencephaly)

Multiple pregnancies

Uterine malformations (bicornuate uterus)

Question 27

Most common classification of breech presentation

Answer 27

Frank — thighs are flexed, lower extremities extended at knees

[next most common is complete where thighs and LEs are flexed, then incomplete where 1 LE is flexed and the other extended]

Question 28

Maneuver that may be applied to breech presentatioin that involves applying pressure to mom’s abdomen to turn the fetus in either a forward or backward somersault to achieve vertex presentation

Answer 28

External cephalic version (ECV)

Question 29

Candidates for external cephalic version must be at least ____ week gestation and NOT in labor

What are some contraindications to ECV?

Answer 29

36

Contraindications: placenta previa, nonreassuring fetal monitoring, oligohydramnios, previous uterine surgery that is contraindication to vaginal delivery

Question 30

Although the standard of care in most practices is to deliver all breech presentations by C section, vaginal delivery may be appropriate in some cases. What are the criteria for vaginal delivery of breech presentation in terms of classification, age, weight, and position

Answer 30

Fetus must be in frank or complete breech presentation

Gestational age >37wks

Fetal weight 2500-4000g

Fetal head must be flexed

Adequate maternal pelvis

Availability of anesthesia and neonatal support

Question 31

What type of forceps are used in assisted vaginal delivery of a breech baby?

Answer 31

Piper forceps

Question 32

Brow presentation occurs when presenting part of fetus is between facial orbits and anterior fontanelle. 50-75% will convert to a face presentation (through extension) or a vertex presentation (through flexion) then deliver. If there is persistent brow presentation, how should you deliver?

Answer 32

C-section! Persistent brow presentation makes vaginal delivery impossible

Question 33

Face presentation is characterized by full extension of the fetal head and neck with occiput against the upper back. ______ is a fetal malformation seen in 1/3 of face presentations

Answer 33

Anencephaly

Question 34

How is delivery method determined when there is a face presentation?

Answer 34

Fetal chin is point of designation

If mentum anterior, you can deliver vaginally

If mentum posterior, you CANNOT deliver vaginally and must proceed with C section

Question 35

Compound presentation is defined as a fetal extremity (usually the hand) is found prolapsed alongside the presenting fetal part (head). This occurs more frequently with premature delivery. How is this managed?

Answer 35

May resolve on its own as it comes down the pelvis. Some recommend gently pushing small part upward while simultaneously applying fundal pressure

If there is failure to progress, cord prolapse, or nonreassuring fetal status, proceed with C section