Flashcards in 12 - Obs - Multiple Pregnancy Deck (5):
Twins 1/??, triplets 1/1000. Geographic variation. Incidence of twins incr due to ? trt and incr no of ? mothers. In UK ? and higher order now ? due to better fertility trt regulation.
DZ twins (?/3 of all multiple pregs) or triplets due to fert of different ? by ? sperm. May be different ? and no more ? similar than normal siblings
MZ twins from mitotic ? of ?
zygote into ? twins. Sharing of ? or ? depends on ? at which division into separate zygotes occurred. Division before day ? (30%) -> twins w ? placentas and amnions (?
? DCDA). Division 4-?days (70%) -> twins w shared ? and separate ? (????). Division ?-13days -> v rare, shared ? and single ?(????). Incomplete division -> ? twins. MC twins have higher fetal ?, esp pre ?wks.
Assisted ?, ? factors and incr maternal ?/? are most important factors, largely affecting ?? twinning. ?% of all IVF conceptions and 5-10% ?-assisted conceptions are multiple.