Dev & Ageing - Disorders of Early Foetal Development Flashcards
What are the reasons for early pregnancy loss? (3)
- Failure in the embryo-foetal development
- Inability to sustain development of implanted embryo/foetus
- Failure of embryo implantation in endometrium
What is a miscarriage?
A loss of pregnancy prior to 23 weeks of gestation
What is an early clinical pregnancy loss
A loss of pregnancy prior to 12 weeks of gestation
What is a late clinical pregnancy loss
A loss of pregnancy after 24 weeks of gestation (stillbirth)
What classifies for recurrent miscarriages/pregnancy loss in the UK
3+ losses
What classifies for recurrent miscarriages/pregnancy loss in the US/Europe
2+ losses
How many pregnancies does recurrent loss affect?
0.8-1.4% of pregnancies
How frequent is clinical pregnancy loss?
Affects 15% of conceptions
What age group is most affected by clinical pregnancy loss?
40-44 year olds
What are the 2 types of clinical pregnancy loss
Live birth
Miscarriage
What are the 2 types of pre-clinical pregnancy loss?
Post-implantation
Pre-implantation
What is one of the major causes for early pregnancy loss?
Aneuploidy
How common is aneuploidy?
- It was found that 53% of IVF donor eggs embryos were aneuploid.
- 50% of lost early pregnancies displayed some chromosomal abnormality
How does maternal age vary with trisomy?
Increase in maternal age increases the risk of trisomy exponentially
Why does maternal age increase the risk of aneuploidy?
Maternal oocytes undergo prolonged meiotic arrest in prophase I
Explain how maternal age increases aneuploid incidence?
During oogenesis, maternal and paternal chromosomes will pair up with their homologues and replicate their DNA.
This will in turn give us 2 chromatids per chromosome, and a pair of each of these chromosomes from the mum and dad.
Genetic material is exhanged between the maternal and paternal homologues via recombination, and they are then held in dictyate arrest until menarche, via cohesin proteins.
With age, we lose cohesins therefore are more likely to split chromosomes, meaning that chromatids drift and will enter eggs in uneven numbers.
What are examples of cohesin proteins?
REC8 and SMC2
What signalling in mice was shown to cause pregnancy loss?
Deficiency of LIF was shown to cause failed implantation despite normal embryo development
What is LIF?
Leukaemia inhibitory factor released from endometrial cells stimulates adhesion from the blastocyst to endometrial cells
How do LIF levels relate to sub fertile women’s uterine secretions?
Reduced levels of LIF were found in the uterine secretions of sub fertile women