Multiple gestation, alloimmunization, and FGR

Question 1

Order of formation of fetal structures in a pregnancy

Answer 1

1. Placenta
2. Membranes
3. Fetuses

Question 2

Monozygotic twins day of zygote division leads to each type of placentation

Answer 2

Day 2-3: dichorionic, diamniotic (25%)
Day 4-7: monochorionic, diamniotic (75%)
Day 8-12: monochorionic, monoamniotic (1-2%)
Day >12: conjoined twins (rare)

Question 3

Timing to best determine chorionicity

Answer 3

6-8 wga (separate sacs and thick membrane vs one sac and thin membrane)

Question 4

How to determine amnionicity at 6-8 wga

Answer 4

Number of yolk sacs = number of amniotic sacs

Question 5

Dichorionic vs monochorionic at >8 wga

Answer 5

Dichorionic = twin peak sign (chorion travels up into division), lambda sign, thicker membrane
Monochorionic = T sign (amnion is only part making division), thin membrane, same gender

Question 6

Mean GA at delivery for singleton vs twin

Answer 6

38.6 wga vs. 35.3 wga

Question 7

How much more likely are twins to deliver preterm than singletons?

Answer 7

6 x (and 13 x for delivery under 32 wga)

Question 8

Other increased risk with twins

Answer 8

Anomalies, prematurity, growth restriction, severe IVH, PVL, cerebral palsy

Question 9

Twin ultrasound surveillance timing

Answer 9

Dichorionic: q4-6 wks starting at 24 wga
Monochorionic: q2wks starting at 16 wga
*AFV/bladders q2wks and growth q4wks

Question 10

Indications for Dopplers in twins

Answer 10

FGR, TTTS

Question 11

Indications for antenatal testing in twins

Answer 11

FGR in either (but not discordance), oligohydramnios, maternal indications, monochorionic placentation

Question 12

When to initiate antenatal testing in monochorionic twins

Answer 12

32 wga

Question 13

Delivery timing for twins

Answer 13

Di-di: 38.0 - 38.6 wga
Mo-di: 34.0 - 37.6 wga
Mo-mo: 32.0 - 34.0 wga

Question 14

Criteria for twin vaginal birth

Answer 14

1. > 32 wga
2. Diamniotic
3. Vertex presenting twin A
4. Twin B any presentation
5. Provider with skills in breech extraction
   (>1500 g, <20% discordance with A bigger)

Question 15

Risk of anomalies for twins

Answer 15

4-10% (1.5 - 2 x higher than singletons)

Question 16

Risk of loss of a fetus in dichorionic twins

Answer 16

20% in first trimester

2-5% in second trimester

Question 17

Risk for remaining twin after loss of one dichorionic

Answer 17

Reduced risks! (and no increased maternal risk)

Question 18

How to define discordance

Answer 18

> 20% (larger - smaller / larger)

Question 19

How to define TTTS

Answer 19

1. MCDA placentation

2. MVP > 8 cm (95%ile) and < 2 cm (5%ile)

Question 20

Quintero sages for TTTS

Answer 20

I. MVP > 8 cm and < 2 cm
II. Absent bladder
III. AEDF, REDF
IV. Hydrops
V. Fetal death

Question 21

Stuck twin

Answer 21

TTTS which looks like mo-mo twins because one is small and has anhydramnios

Question 22

How to manage stage I TTTS

Answer 22

Expectant (15% progress)

Question 23

How to manage stage II-IV TTTS

Answer 23

<26 wga: fetoscopic laser

>26 wga: delivery

Question 24

Management of monoamniotic twins

Answer 24

No one knows right answer; deliver at 32-34 wga if stable

Question 25

Antibodies that can cause fetal disease bad enough to require transfusion

Answer 25

Kell, RhD, Rhc

Question 26

Antibodies that cause mild disease

Answer 26

Duffy, Kidd, RhC, RhE, Rhe

Question 27

Dose of Rhogam and amount of fetal blood covered

Answer 27

300 mcg, 30 mL of blood

Question 28

What to do at delivery if fetus Rh pos

Answer 28

If neonate Rh pos, give Rhogam and perform fetal KB to determine if additional needed (unlikely)

Question 29

Risk of alloimmunization if Rhogam not given

Answer 29

17%

Question 30

Timing for titers in known isoimmunization

Answer 30

< 24 wga: monthly titers | > 24 wga: q2wk titers

Question 31

What is critical titer and what to do?

Answer 31

1:8 (or up to 1:32) | Start MCA Dopplers q1-2 wks

Question 32

What to do if history of affected fetus?

Answer 32

Titers not predictive; if father heterozygous, do amnio or cffDNA; if homozygous or unknown, do MCA Dopplers at 18 wga

Question 33

Second most common cause of neonatal morbidity and mortality (after prematurity)

Answer 33

FGR

Question 34

How many fetuses <10%ile in growth are normal?

Answer 34

70%

Question 35

SGA vs low birth weight

Answer 35

Born at <10%ile vs cut-offs of 2500 g (LBW), 1500 g (VLBW), <1000 g (ELBW)

Question 36

Long-term effects of FGR

Answer 36

2x risk of cognitive delay, risks of CV disease, obesity, and diabetes

Question 37

Likelihood of FGR with history of FGR

Answer 37

25% if once | 50% if twice

Question 38

How common is oligo in FGR?

Answer 38

75%

Question 39

Normal UA Dopplers

Answer 39

"Rule of thumb" = 30 wga, 3.0 | S/D steadily declines throughout pregnancy

Question 40

When to do amnio in setting of FGR

Answer 40

1. Dx at <32 wga 2. FGR + polyhydramnios 3. FGR + anomaly (do microarray and CMV PCR)