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Fetopathology and developmental pathology of the embryo and fetus
Marta Ježová, Josef Feit et al.
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Pathology of twinning
Marta Ježová
Introduction

Multiple pregnancy in human is not a physiological event because the anatomy of the human uterus is designed to harbour only one fetus at a time.

  • complications depend on the type of placentation
  • monochorionic twins especially show a high incidence of intrauterine and perinatal complications
Etiology
  • dizygotic twins:
    • 11 – 12 : 1000 childbirths in our population i.e. every 80 – 90th childbirth
    • incidence is strongly affected by race, heredity, number of previous pregnancies, and maternal age (incidence is higher among multiparas; there is a hereditary trait on the mother's side)
  • monozygotic twins:
    • 3.5 – 4 : 1000 childbirths
    • incidence is not influenced by any of the factors mentioned above
  • with IVF/ET (ovulation induction, transfer of a more than one embryo) the incidence of twins is even 20× higher than in a case of spontanous conception
Classification
  • forms of fertilization:
    • dizygotic (biovular): two eggs are fertilized, the fetuses may or may not be of the same sex
    • monozygotic (uniovular): only one egg is fertilized, which later divides into 2 embryos, always of the same sex.
  • forms of placentation:
    • completely separate placentae.
    • dichorionic diamnionic placenta: two fetuses nidate close together and their two separate placentas fuse, so that they macroscopically look like a single placenta. Septum between the fetuses is thick and non-transparent, formed by these layers: amnion —  chorion — chorion — amnion. Blood circulations of the fetuses remain separate.
    • monochorionic diamnionic: single placenta, the twins share one vascular chorion but each fetus is in its own amnionic cavity. The septum between the twins is thin and transparent (made up of two layers of amnion only). Blood circulations are often connected.
    • monochorionic monoamnionic: The twins share both chorion and amnion, there is no septum between them. Blood circulations are heavily interconnected.
  • zygosity and placentation, the rules:
    • dizygotic twins: each has its own placenta, but these can fuse together (dichorionic diamnionic)
    • monozygotic twins: more complicated, type of placentation depends on the timing of the twinning event:
      • 0 – 2nd day: dichorionic diamnionic or even completely separate placentas
      • 2 – 9th day after fertilization: monochorionic diamnionic, this form is most frequent
      • 9 – 13th day: monochorionic monoamnionic
      • A very rare anomaly are so-called Siamese twins (conjoined twins). The twinning event occurs late (13 – 14 day) the zygote fails to split completely. These twins always share one placenta and one umbilical cord and also share various body parts and internal organs (this is not the result of fusion of the twins). For more detailes see the chapter Monsters.

Placenta of biamnial biplacental twins (73280)

Twins and bichorial biamnial placenta (73974)

Pictures

Placenta of biamnial biplacental twins: Biamnial bichorial placenta, twins, Macro, autopsy (73279)

Another case: Biamnial bichorial placenta, twins, Macro, autopsy (73280)

Twins and bichorial biamnial placenta: Placenta, twins, Macro, autopsy (73974)

Bichorial biamnial placenta: Placenta, bichoriadal biamnial twins, Macro, autopsy (73996)

Clinical signs
  • higher mortality and morbidity of twins compared to singletons
    • pathology during intrauterine developement is due to:
      • umbilical cord accidents
      • twin transfusion syndrome
      • slightly higher incidence of congenital malformations
    • pathology of delivery:
      • preterm labor
      • pathology of the second stage of delivery
      • hypoxia, twin B is in risk
    • postpartum period: complications related to prematurity because most twins are born before 37th w.g.
  • there are also well known risks for the mother:
    • higher incidence of preeclampsia
    • hyperemesis gravidarum
    • high incidence of cesearean section delivery

Fetal death in multiple pregnancy:

Suprisingly many pregnancies begin as multiple, but one fetus usually dies sooner than multiple gravidity is recognized (before 10th w.g):

  • the dead embryo may be completely resorbed
  • the dead embryo remains as a small amorphous disk in the fetal membranes of the surviving twin —  vanishing twin syndrome
  • if one fetus demises in later stages of development, the dessicated body is compressed which is calles fetus compressus (fetus papyraceus)
Pictures

Fetus compressus, two placentas with minimal fusion: Twins, fetus papyraceus, Macro, autopsy (72393) Twins, fetus papyraceus, Macro, autopsy (72394) Twins, fetus papyraceus, Macro, autopsy (72395)

Vanishing twin: Vanishing twin, Macro, autopsy (73072) Vanishing twin, Macro, autopsy (73073) Vanishing twin, Macro, autopsy (73074)

Triplets, fetoreduction: Triplets, fetal reduction, Macro, autopsy (73342) Triplets, fetal reduction, Macro, autopsy (73343) Triplets, fetal reduction, Macro, autopsy (73344)

Complications of monochorionic diamnionic placentation
Complications of monochorionic monoamnionic placentation
Congenital malformations in twins
Pathology of higher multiple gestations: triplets
Monsters