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Posted on October 4, 2019 at 1:06 AM

Readers of this blog may have seen the report in the general press that,
after three decades of increases, the rate of twin births in the U.S. has
declined by 4% from 2014 to 2018.

Those three decades correspond to the era of IVF, since the birth of
Louise Brown in England in 1978.  It
seems likely that changes in IVF practice contributes at least in part, if not
substantially, to the trend in twin births.

Specifically, doctors at IVF clinics are more commonly implanting only
one, rather than more than one, embryo back into a prospective mother’s womb with
each attempt at a live birth.  Multiple
pregnancies—even twins, not just “Octomom” scenarios—carry
increased risk for mother and babies. 
Previously, two or more embryos were implanted in an effort to increase
the chance that at least one would make it to live birth.  Sometimes, “selective abortion” was
practiced to reduce the number of initially multiple pregnancies to one.  Now, it appears that gradually increasing
success rates of IVF are supporting single-embryo transfer as a standard
practice.

The Centers for Disease Control and Prevention (CDC), which provides a substantial
amount of information
on the current status of IVF on its website, summarizes
the changes
in the percentage
of single-embryo transfers in recent years—increasing from
11.6% of non-donor-egg transfers in 2007 to 39.9% in 2016.

To the extent that this reduces the practice of selective abortion and,
one hopes, decreases the number of embryos created but kept frozen, never to be
born, at IVF clinics, this is a welcome development.  The Christian Medical Dental
Association takes the position
that, in IVF, the number of embryos should
be kept to a minimum, and all embryos created should be so created with the
intent of having the genetic mother carry all of them in pregnancy, to live
birth one hopes.

IVF remains a transformative enabling technology that facilitates
contractual arrangements for reproduction, profound changes in the structure of
families, and the use of pre-implantation genetic diagnosis to control what
sort of people are allowed to be born. 
One might view these developments as non-physical harms, that alter our overall
experience of being human in ways that may properly be subject to question.

And: the rate of twin birth is still twice what it was in 1980.  If one sees a mom or dad pushing a stroller
with fraternal twins, chances are they are IVF kids.

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