Fewer U.S. Twins and the Development of IVF

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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