30 Questions
What is the definition of twinning?
The bearing of two children at one birth
What percentage of twins are dizygotic (fraternal) twins?
90%
What is the incidence of monozygotic (identical) twins per 1000 births?
3-4 per 1000 births
What is a factor that increases the chances of twinning?
Advancing age of the mother
What is the racial group with the highest incidence of twinning?
Black African women
What is a method that increases the chances of twinning?
Assisted reproductive techniques or IVF
How are dizygotic twins created?
After the ovulation of two oocytes, which are fertilized by two different sperms
What is a characteristic of dizygotic twins?
They are genetically different
How are the zygotes implanted in the uterus in dizygotic twins?
Separately in the uterus
What is the likelihood of a woman conceiving fraternal twins if she is a fraternal twin?
Higher
What is the result of the inner cell mass splitting in a blastocyst?
Two completely separate embryos with a common placenta and separate amniotic cavities
What is the rare case of monozygotic twins?
Separation at the bilaminar germ disc stage
What is the percentage of women who give birth to two babies when pregnant with twins?
29%
What is the outcome of twin-twin transfusion syndrome?
Blood flow to one of the twins is more with poor outcome
What are conjoined twins also known as?
Siamese twins
What is the result of incomplete separation of the inner cell mass?
Conjoined twins
What is the type of conjoined twins where bodies are fused from the upper chest to the lower chest?
Thoraco-omphalopagus
What is the incidence of low birth rate in twins?
Higher than singletons
What is the mortality rate of twins compared to singletons?
3 times higher
What is the percentage of twins born preterm?
60%
What occurs in dizygotic twins during implantation?
The zygote implants individually at distant sites in the uterus
What is a characteristic of erythrocyte mosaicism in dizygotic twins?
Each twin has two types of red blood cells
What is a characteristic of monozygotic twins?
They have exactly the same genetic information
What is one way monozygotic twins can arise?
Subdivision and splitting of a single embryo
What happens when the zygote splits at the two-cell stage in monozygotic twins?
Two separate embryos develop with separate placentas
What is the arrangement of membranes in monozygotic twins that split at the two-cell stage?
Similar to dizygotic twins
How can monozygotic twins be recognized?
By their strong resemblance in blood groups, fingerprints, sex, and external appearance
At what stages can the zygote split to form monozygotic twins?
At various stages, including the two-cell stage and the blastocyst stage
What is a characteristic of the implantation of dizygotic twins?
The two zygotes implant at distant sites
What can occur when the walls of the chorionic sac fuse in dizygotic twins?
The two chorionic sacs fuse
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