Pocket ObGyn – Multiple Gestation

Dec 9, 2019 admin SẢN KHOA 0

Pocket ObGyn – Multiple Gestation
See Abbreviations

Definition and Epidemiology (Obstet Gynecol 2014;123:1118)

  • Pregnancies in which more than one fetus implants in the uterus
  • Multi gestations account for 3% of all births
  • 65% rise in twins & 500% rise in triplets or higher since 2002, likely secondary to ART
Etiology
  • Described in terms of zygosity – number of eggs initially fertilized

Monozygotic = one egg fertilized by one sperm; splitting of initial zygote

Dizygotic = usu two eggs fertilized by two sperm; two separate fertilization events

  • Chorionicity vs. amnionicity

Determined by timing of embryonic splitting

0–4 d after fertilization ® dichorionic diamnionic twins 4–8 d after fertilization ® monochorionic diamnionic twins

8–12 d after fertilization ® monochorionic monoamnionic twins

>12 d post fertilization ® conjoined twins

Chorionicity: Number of placentas shared by embryos (di = 2, mono = 1)

Amnionicity: Number of amnionic sacs around embryos (mono = both embryos in 1 sac)

Physical Exam
  • Measurement of size > dates
Diagnostic Workup/Studies
  • Best test is US in early Preg ® determines number of embryos Cannot always tell chorionicity

1st trimester twin peak sign = dichorionic gest

Figure 11.1 A: Monochorionic diamnionic twins have fused amnionic membranes with no intervening placental tissue (<1 mm thick). B: Dichorionic diamnionic twins show twin peak sign with membrane separation and intervening chorion

 

A

 

Amnion

 

 

 

Twin A

        

 

 

 

 

 

 

Twin B
   
Placenta

Complications
  • Almost all complications of Preg are more likely w/ multi gestations
  • Discordance: One twin larger than the other; clinically signif when greater than 20%. Calculate discordance % as: [(larger EFW – smaller EFW) / larger EFW] ´
  • Monochorionic monoamnionic twins: Cord entanglement & subseq cord accident; delivered early at 32–34 w
  • Monochorionic diamnionic twins: Twin to twin transfusion syndrome (TTTS) Due to bld vessel anastomoses w/i single placenta w/ pressure diff

Occurs in ~15% of monochorionic diamniotic twin gestations

Donor twin: Bld shunted away Recipient twin: Bld shunted toward Stages of TTTS (J Perinatol 1999;19:550):

  1. Polyhydramnios/oligohydramnios, donor bladder present
  2. Poly/oli, donor bladder absent
  3. Poly/oli, abn Dopplers
  4. Poly/oli, hydrops of recipient
  5. IUFD of one or both fetuses
Rx:

Laser photocoagulation of vessel anastomoses (Stage II or worse) Serial amnioreduction

Selective reduction (termination) of one fetus

See Abbreviations

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