Multiple gestation, alloimmunization, and FGR Flashcards
Order of formation of fetal structures in a pregnancy
- Placenta
- Membranes
- Fetuses
Monozygotic twins day of zygote division leads to each type of placentation
Day 2-3: dichorionic, diamniotic (25%)
Day 4-7: monochorionic, diamniotic (75%)
Day 8-12: monochorionic, monoamniotic (1-2%)
Day >12: conjoined twins (rare)
Timing to best determine chorionicity
6-8 wga (separate sacs and thick membrane vs one sac and thin membrane)
How to determine amnionicity at 6-8 wga
Number of yolk sacs = number of amniotic sacs
Dichorionic vs monochorionic at >8 wga
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
Mean GA at delivery for singleton vs twin
38.6 wga vs. 35.3 wga
How much more likely are twins to deliver preterm than singletons?
6 x (and 13 x for delivery under 32 wga)
Other increased risk with twins
Anomalies, prematurity, growth restriction, severe IVH, PVL, cerebral palsy
Twin ultrasound surveillance timing
Dichorionic: q4-6 wks starting at 24 wga
Monochorionic: q2wks starting at 16 wga
*AFV/bladders q2wks and growth q4wks
Indications for Dopplers in twins
FGR, TTTS
Indications for antenatal testing in twins
FGR in either (but not discordance), oligohydramnios, maternal indications, monochorionic placentation
When to initiate antenatal testing in monochorionic twins
32 wga
Delivery timing for twins
Di-di: 38.0 - 38.6 wga
Mo-di: 34.0 - 37.6 wga
Mo-mo: 32.0 - 34.0 wga
Criteria for twin vaginal birth
- > 32 wga
- Diamniotic
- Vertex presenting twin A
- Twin B any presentation
- Provider with skills in breech extraction
(>1500 g, <20% discordance with A bigger)
Risk of anomalies for twins
4-10% (1.5 - 2 x higher than singletons)
Risk of loss of a fetus in dichorionic twins
20% in first trimester
2-5% in second trimester
Risk for remaining twin after loss of one dichorionic
Reduced risks! (and no increased maternal risk)
How to define discordance
> 20% (larger - smaller / larger)
How to define TTTS
- MCDA placentation
2. MVP > 8 cm (95%ile) and < 2 cm (5%ile)
Quintero sages for TTTS
I. MVP > 8 cm and < 2 cm II. Absent bladder III. AEDF, REDF IV. Hydrops V. Fetal death
Stuck twin
TTTS which looks like mo-mo twins because one is small and has anhydramnios
How to manage stage I TTTS
Expectant (15% progress)
How to manage stage II-IV TTTS
<26 wga: fetoscopic laser
>26 wga: delivery
Management of monoamniotic twins
No one knows right answer; deliver at 32-34 wga if stable
Antibodies that can cause fetal disease bad enough to require transfusion
Kell, RhD, Rhc
Antibodies that cause mild disease
Duffy, Kidd, RhC, RhE, Rhe
Dose of Rhogam and amount of fetal blood covered
300 mcg, 30 mL of blood
What to do at delivery if fetus Rh pos
If neonate Rh pos, give Rhogam and perform fetal KB to determine if additional needed (unlikely)
Risk of alloimmunization if Rhogam not given
17%
Timing for titers in known isoimmunization
< 24 wga: monthly titers
> 24 wga: q2wk titers
What is critical titer and what to do?
1:8 (or up to 1:32)
Start MCA Dopplers q1-2 wks
What to do if history of affected fetus?
Titers not predictive; if father heterozygous, do amnio or cffDNA; if homozygous or unknown, do MCA Dopplers at 18 wga
Second most common cause of neonatal morbidity and mortality (after prematurity)
FGR
How many fetuses <10%ile in growth are normal?
70%
SGA vs low birth weight
Born at <10%ile vs cut-offs of 2500 g (LBW), 1500 g (VLBW), <1000 g (ELBW)
Long-term effects of FGR
2x risk of cognitive delay, risks of CV disease, obesity, and diabetes
Likelihood of FGR with history of FGR
25% if once
50% if twice
How common is oligo in FGR?
75%
Normal UA Dopplers
“Rule of thumb” = 30 wga, 3.0
S/D steadily declines throughout pregnancy
When to do amnio in setting of FGR
- Dx at <32 wga
- FGR + polyhydramnios
- FGR + anomaly
(do microarray and CMV PCR)
