A Dynamic Model of Amniocentesis

V. Joseph Hotz, University of California at Los Angeles
Seth G. Sanders, University of Maryland

Medical Practitioners have clear advice on amniocentesis for women as they age. Doctors advise women to be tested for Downs Syndrome and other genetic disorders after age 35. Prior to age 35, these tests are discouraged as it can cause a miscarriage. The logic appears compelling. The rate at which amniocentesis causes miscarriages is age-invariant while the rate of genetic disorder rises substantially over a woman's reproductive years. Hence the potential benefit (by terminating an unwanted fetus with a genetic disorder) from testing rises as well. This paper argues that this logic is flawed. We develop a dynamic model of a couple's timing of births, decision to have an amniocentesis and have an induced abortion. We show that under reasonable parameters for the growth rate of chromosomal abnormalities, fertility rates and the rate of miscarriage following amniocentesis, optimally chosen amniocentesis can imply a falling rate of amniocentesis as women age.