Chromosome errors are remarkably common in early human development, with an abnormality in chromosome number estimated to be present in over 20% of fertilized eggs and an even greater proportion of day-3 embryos (due to errors arising in the first few cell divisions). As women delay child bearing until late in their fertile life, the risk of miscarriage, pregnancy complications and infertility increases dramatically (see figures). While many of these abnormal embryos may not implant, others do and can contribute to miscarriage, birth defects, and abnormal placental findings. Furthermore, some embryos may have normal numbers of chromosomes but may have epigenetic errors–abnormalities in the way the DNA is packaged into chromosomes that affect how genes are expressed and individuals develop.
Our lab is interested in three main types of errors that may occur in early human development:
- segregation errors involving whole maternal or paternal genomes
- segregation errors involving single chromosomes leading to trisomy (one too many) or monosomy (one too few) chromosomes
- epigenetic errors-particularly in placental cells
It is important to note that the increase in miscarriage with maternal age is primarily due to trisomy.
One of the least obvious (for the public) factors driving infertility issues is the increased in age of mothers at first birth that has risen dramatically in the lase few decades.