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Confined placental mosaicism and intrauterine fetal growth
  1. Valia S Lestoua,
  2. Dagmar K Kalousekb
  1. aDepartment of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, Canada, bBritish Colombia Research Institute for Children’s and Women’s Health, Vancouver, Canada
  1. Dr Dagmar K Kalousek, British Colombia.’s Children’s and Women’s Hospitals, 4480 Oak Street, Vancouver, BC, Canada V6H 3V4. Email: dkalousek{at}

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Fetal growth is a complex and dynamic process regulated by a large number of interactive factors of fetal, maternal, and placental origin. As a result, any abnormality of fetal growth has a complex multifactorial pathogenesis. It has been estimated that about 50% of intrauterine fetal growth is determined by fetal genes.1Maternal disease, her nutritional intake and behaviours, such as smoking, also influence fetal growth. The placenta develops to its full size during the second trimester, to facilitate the fetal growth acceleration after 20 weeks of gestation. An abnormal pattern of placental growth earlier in gestation may result in abnormal fetal growth in the late second or third trimesters.

Key Messages

  • IUGR and SGA occur in about 10% of pregnancies and both are associated with an increased risk for perinatal morbidity and mortality.

  • Environmental and genetic factors are known to be associated with IUGR, although the aetiology of most IUGR remains unexplained.

  • In over 20% of pregnancies with idiopathic IUGR, chromosomal mosaicism confined to extra embryonic tissues (CPM) has been observed. The type of CPM (I–III), the particular chromosomal involvement and the origin of trisomy (mitotic/meiotic) in the aneuploid clone correlate with specific pregnancy outcomes. When meiotic CPM involving trisomy is detected in the placenta, the fetus/neonate has a high risk of having uniparental disomy for that chromosomal pair which is trisomic in the placenta.

  • It is important to study placentas from pregnancies with idiopathic IUGR for the presence of CPM using molecular cytogenetic methods.

  • Detection of CPM not only explains the pathogenesis of fetal IUGR but also provides important information for postnatal follow up.

A recently described genetic condition, confined placental mosaicism (CPM), has been shown to cause clinically significant intrauterine growth restriction (IUGR) or even intrauterine fetal death. CPM is the most common form of constitutional chromosomal …

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