Based on recent (2005) US NCHS data, the rate of multiple births is now approximately 3.4% (4,138,349 total births, of which 139,816 were<unk> s or higher-order multiple births). The majority of identical<unk> s share a common (monochorionic) placenta, and of these approximately 15% go on to develop<unk> . By extrapolating the number of expected identical<unk> s (about one-third) from annual multiple births, and the number of<unk> s with monochorionic placentae (about two-thirds), and from these the number thought to develop<unk>  (about 15%), there are at least 4,500<unk>  cases per year in the U.S. alone: 139,816 × .33 × .66 × .15 = 4,568 cases of<unk>  per year in U.S. (involving more than 9,000 babies.) Since spontaneous pregnancy losses and terminations that occur prior to 20 weeks go uncounted by the C.D.C., this estimate of<unk>  cases may be very conservative. Although infertility treatments have increased the rate of multiple birth, they have not appreciably diluted the expected incidence of identical<unk> s. Studies show a higher rate of identical<unk> s (up to 20 times with IVF) using these treatments versus spontaneous pregnancy rates. One Australian study, however, noted an occurrence of only 1 in 4,170 pregnancies, or 1 in 58<unk>  gestations. This distinction could be partly explained by the "hidden mortality" associated with MC multifetal pregnancies—instances lost due to premature rupture of membrane (PROM) or intrauterine fetal demise before a thorough diagnosis of<unk>  can be made.
Twin-to-twin transfusion syndrome
Neonatal meningitis
Hemolytic disease of the newborn
Hemolytic disease of the newborn 
Shaken baby syndrome
Neonatal toxic shock-like exanthematous disease
Michelin tire baby syndrome
Neonatal sepsis