 Based on 2005 USA National Center
for Health Statistics (4,138,349 total births), the rate of multiple births per year
is now 1:30 (3.4%), or approximately 139,816 twins or higher multiples.
The majority of identical twins
share a common (monochorionic) placenta, and of these approximately 15% go on to
develop TTTS.
.·
By extrapolating the number of expected identical twins (about one-third) from annual multiple
births, and the number of twins with monochorionic placentas (about two-thirds), and from these
the number thought to develop TTTS (about 15%), there are at least 4,500 TTTS cases per year
in the U.S. alone:
139,816 X .33 X .66 X .15 = 4,568 cases of TTTS per year in U.S. (involving 9,500 or more
babies)
Since spontaneous pregnancy loss
(spontaneous abortion) and pregnancy terminations (elective abortions or embryo
reductions) that occur prior to 20 weeks go uncounted in the USA, this estimate
of TTTS may be conservative.
Although infertility treatments
have increased the rate of multiple birth, they have not diluted the expected
incidence of identical twins even though multiple embryos are often produced and
implanted. Studies show a higher rate of identical twins (up to 20 times with IVF)
in women having these treatments than occur naturally.
| There is approximately a 1 in 1000 chance of having TTTS
in a given pregnancy. |
|
