Purpose and Goal: CNEP # 2047

  • Understand vanishing twin syndrome in pregnancy.
  • Learn about how reabsorbed twins effect surviving twins.

None of the planners, faculty or content specialists has any conflict of interest or will be presenting any off-label product use. This presentation has no commercial support or sponsorship, nor is it co-sponsored.

Requirements for Successful Completion

  • Successfully complete the post-test
  • Complete the evaluation form

Date

  • September 2016 – September 2018

Learning Objectives

  • Describe the pathophysiology of vanishing twin syndrome.
  • Describe the neonatal effects of vanishing twins on surviving twins.
  • Identify 2 approaches for the diagnosis and treatment of chimeric karyotypes.

Introduction

  • Vanishing twin syndrome occurs:
    • With a set of twins
    • With a set of multiples
  • It occurs when a fetus disappears in the uterus
  • The timing of this event determines the outcome:
    • For the mother
    • For the surviving fetus

Vanishing Twin Syndrome

  • Vanishing twin syndrome was first noted in 1945
  • It is the identification of multi-fetal gestation:
    • With subsequent disappearance of a fetus
    • The fetus can be reabsorbed by :
      • The mother
      • The surviving fetus
  • The overall rate of multi-fetal gestations:
    • Is 3-6% at 8 weeks gestation
  • The rate of multi-fetal gestation:
    • Is higher at conception
    • Than at the time of birth
  • The loss if a twin can be expected:
    • In up to 7-40% of spontaneous pregnancies
    • In up to 27-38% of assisted pregnancies
  • Vanishing twin syndrome:
    • Occurs in 21-30% of multi-fetal pregnancies
    • This holds true in the USA and Europe
  • It has been described more frequently:
    • With early pregnancy ultrasounds
    • With in vitro fertilization (IVF)
      • IVF pregnancies are closely followed
      • The number of implanted eggs is known
  • The timing of this event significantly:
    • Affects maternal complications
    • Affects the outcome of the viable twin

Pathophysiology

  • The cause of a vanishing twin is unknown
    • Could be associated with congenital anomalies
    • Could be associated with abnormal implantation
  • Abnormalities developing from a vanishing twin:
    • Usually appear early in development
    • As opposed to a later acute insult
  • Placental or fetal analysis frequently reveals:
    • Chromosomal abnormalities
      • Diplody
      • Triplody
      • Abnormal sex chromosomes
  • Chromosomal abnormalities may be found in:
    • Skin biopsies
    • Placental pathology
    • Chorionic villi sampling
  • Chromosomal analysis of the surviving twin:
    • Is generally normal
  • It is widely thought that the vanishing twin:
    • Had a chromosomal abnormality
    • That resulted in the disappearance
  • With vanishing twin syndrome there may be:
    • Complete reabsorption of the fetus
    • Formation of a fetus papyraceus
      • A “mummified” fetus
      • A compressed fetus
    • Development of a subtle placenta abnormality
      • Placental cyst
      • Subchorionic fibrin
      • Amorphous material

Maternal Morbidity

  • First trimester morbidity is limited
    • Mild vaginal bleeding
    • Mild uterine cramping
  • Second and third trimesters
    • Premature labor
      • Significantly increases
      • Preterm < 37 weeks
      • Very preterm < 32 weeks
  • Infection from retained fetus
  • Severe puerperal hemorrhage
  • Consumptive coagulopathy
  • Obstruction of labor
    • Low lying papyraceus
    • Causing labor dystocia
    • Leading to Cesarean section
  • Emotional stress from loss of twin
    • Grief and bereavement

Fetal Morbidity and Mortality

  • The surviving fetus
    • Loses a twin
    • Is at risk for hypotension
      • At the time of disappearance
    • Is at risk for poor perfusion
      • At the time of disappearance
    • Is at risk for skin necrosis
      • Cutis aplasia
      • Results from hypotension
    • Is at risk for cerebral palsy
  • Complications are generally low
    • If the event occurs early
  • Complications can be more severe
    • If the event occurs in the first trimester
      • The surviving twin can be flattened
      • From vanishing amniotic fluid absorption
      • From vanishing placental tissue absorption
    • If the event occurs in the third trimester
      • Miscarriage of both twins can occur

Neonatal Complications

  • Prematurity
    • There is a high risk of prematurity
    • At least 23% are born premature
    • Many are born < 32 weeks gestation
  • Low birth weight or SGA
    • There is a high risk of low birthweight
    • At least 33% are born SGA
    • Many require NICU care
  • Chimeric genetic disorders
  • Cerebral palsy (CP)
    • There is an increased risk of CP
    • Related to release of thromboplastic proteins
      • Absorption of proteins by surviving twin
      • Which leads to reverse blood flow
      • Which leads to coagulopathy
      • Which leads to CNS damage
    • Related to hypotension from reverse blood flow
      • Which leads to IVH
  • Congenital anomalies
    • Microcephaly
    • Hydrocephaly
    • Eye anomalies
    • Cleft lip/palate
    • Cardiac anomalies

Chimeric Genetic Disorders

  • A chimeric genetic disorder refers to:
    • Possession of more than one genetic identity
    • It can refer to animals or humans
  • The term chimera comes from ancient mythology
    • Chimeras were incredible beasts
    • They were a composite of two creatures
      • With a lion’s head
      • And a serpent’s tail
  • In humans, chimeras are composites of two embryos
    • The embryos becomes fused in utero
    • This is considered to be very rare
  • Chimeric disorders are known as 46 XX/46 XY karyotypes
  • They are caused by having two distinct cell populations
  • They arise from the combination of an XX zygote and an XY zygote
  • The two zygotes would have normally developed into twins
    • 46 XX/46 XY is associated with ambiguous genitalia
  • Physical symptoms vary widely from infant to infant
  • The most common symptoms are:
    • A small phallus
      • Midway in size
      • Between a clitoris and a penis
    • An incompletely closed urogenital opening
      • Or a shallow vagina
    • An abnormal urethra opening
      • Located on the perineum
  • Infants possess both ovarian and testicular tissue
    • The ovaries may function fully, partly or not at all
    • The testes may function fully, partly, or not at all
  • Segmentation of skin (distinct patches) may be seen
  • Different colored eyes may also be seen (this is rare)
  • 46 XX/46 XY does not involve cognitive impairment
  • At puberty, male and female characteristics may emerge
  • Genetic testing is the only reliable method of diagnosis

Differences in Sexual Development

  • Infants with ambiguous genitalia
    • Should be considered gender neutral
    • Should be referred for specialty care
  • The Differences in Sexual Development Clinic
    • Urology
    • Endocrinology
    • Genetics
    • Cytogenetics
    • Gynecology
    • Psychiatry
    • Adolescent Medicine
  • Diagnosis is based on several studies:
    • Physical examination
    • DNA studies
    • Cytogenetic studies
    • Hormonal studies
    • Radiographical evaluation
    • Ultrasonography evaluation
    • Endoscopic studies
    • Laparoscopic studies
    • Psychosocial assessment
  • Treatment involves several approaches:
    • Hormonal treatment
    • Nonsurgical treatment
      • Vaginal dilation
    • Surgical treatment
      • Creation of genitals
      • Genital reconstruction
    • Psychosocial support
    • Long term follow up and support
  • Goals of treatment include:
    • Education
      • Family
      • Healthcare providers
    • Counseling and support
      • A conflict of identity should be anticipated
      • Sexual confusion should be anticipated
      • Sexual disorientation should be anticipated

Summary

  • Vanishing twin syndrome is relatively common
  • There is little physical effect on the mother
  • There can be considerable effect on the surviving twin
    • Human chimeric disorders may be seen
  • All infants with ambiguous genitalia
    • Should be considered gender neutral
    • Should be referred for specialty care
    • DNA studies should guide sex assignment

References

  1. Anderson-Berry, A.L. 2016. Vanishing Twin Syndrome. Medscape.
  2. Landy, H.J & Keith, L.G. 1998. The Vanishing Twin: A Review. Human Reproduction Update, 4 (2), p. 177-183.
  3. Niu, D.M., Pan, C.C. Lin, C.Y., Hwang, B.T., and Chung, M.Y. 2002. Mosaic or Chimera? Revisiting an Old Hypothesis About the Cause of 46,XX/46,XY Hermaphrodite. Journal of Pediatrics, 140 (6), p. 732–735.

Evaluation

*Required fields