Multiple Pregnancy Flashcards
What are the two types of twins you can get?
Dizygotic and monozygotic
Are multiple pregnancies increasing?
Yes
What occurs to get dizygotic twins?
Two sperm fertilises two seperate eggs and they are no more related than non-twin siblings
What makes a monozygotic set of twins?
One egg and one sperm. The egg splits after fertilisation - they share all DNA and appear identical
What are the types of triplets you can get?
One zygote - all identical
Two zygotes - one pair of identical twins and one non identical
Three zygotes - three sperm
What is chorionicity?
Twins can have different types of chorions depending on when they split.
What type of chorions and amnions does a dichorionic diamniotic twins have?
Two chorions, two amnions (one each) they also have different placenta
What amnions and chorions do monochorionic diamniotic twins have?
One chorion, two amnions and share one placenta
What amnions and chorions do monochorionic monoamniotic twins have?
One chorion one amnion and one placenta to share
What type of chorionicity are monozygotic twins?
All - monochorionic monoamniotic/ monochorionic diamnioitic/ dichorionic or diamniotic
What type of chorionicity do dizygotic twins have?
Only dichorionic diamniotic
Can the placenta fuse in dizygotic twins?
Yes
How can monozygotic twins have different chorionicity?
Depends on the time they split.
If the eggs split day 1 - 3 no structures have been made and so they will make their own and be DC/DA
If the zygote splits day 4 - 8 they will have seperate chorions but share an amnion (MC/DA) as the amnions develop before the chorion.
What happens if twinning occurs after day 13?
Conjoined twins
What are conjoined twins?
Twins which are joined together somewhere on their body due to not correctly splitting
What is twin to twin transfusion syndrome?
Happens is MC/DA pregnancies and involves the placenta vascularising so that one twin gets more blood than the other
What are mirror image twins?
Happen in MZ twins when they split as the cells become opposite on another - this means they both look alike but minor features are on opposite sides e.g handedness, wrinkles etc.
Has the multiple birth rate increased?
Yes - its more common in Africa
Does IVF cause an increase in multiples?
Yes
Why does ART increase the amount of multiple births?
Because more embryos are put back and also the drugs used can increase ovulation.
Is there a campaign to try and stop multiple pregnancies through IVF?
Yes as multiple births are dangerous
do all countries only put 1 - 3 embryos back?
no america will put up to 8 back
Why does IVF increase the chances of having identical twins and not non-identical twins?
The zona pellucida might alter (hardening) depending on the drugs being used and therefore might be more likely to split.
Does increased age makes you more likely to get multiple births?
Yes - over 35 = twice as likely to have twins
Why might older mothers have twins?
s someone gets older there is less follicles and less inhibin which increases the amount of FSH which could influence how many eggs ovulate
Could increasing the amount of ovulation be an evolution strategy?
Yes as in older women there is less chance of young surviving and so if you have 2 you might get 1 live birth. But obviously if they are both healthy you get twins
What makes you more likely to have dizygotic twins?
Common in some ethnic groups
DZ runs in mothers side of the family
How could genetics influence twins?
Ovulation is controlled by FSH, GDF9 and BMP15. Mutations in either BMP15 and GDF9 has been associated with increased DZ twins.
Sequence variation of FSH and SMAD3 increases chance of DZ in women
Are there genetic causes of MZ twins?
Not really as they don’t run in families however familial MZ twins can transmit from mother or father (suggests an inherited defect) and mutation in zona pellucida leads to failure/delay of cell to cell recognition or adhesion
What are semi identical twins?
A first trimester twin scan showed a monochorionic diamnotic twins (should be identical).
The second scan showed twin A was male and twin B was female.
They did a genetic analysis and found that they shared 75% DNA - an identical maternal allele but different paternal alleles.
How do semi identical twins develop (Sesquizygous twins)
Two sperm fertilise an egg creating 3 cells (this should only be two) The two cells divide and a twinning event occurs - one takes an XY the other XX (the twins are chimeras)
