Immunosuppressive therapy is commonplace in the modern practice of med
icine. For some conditions, such as organ transplantations, new and mo
re aggressive treatments have improved the feasibility of pregnancy in
women who are invariably taking immunosuppressive agents. For other c
onditions, such as moderate-to-severe asthma or systemic lupus erythem
atosus, better immunosuppressive regimens and a shift in medical opini
on regarding the advisability of pregnancy have led to increased numbe
rs of affected women who choose to become pregnant. One of the most dr
amatic advances in modern medicine, a combination of high-dose chemoth
erapy with allogenic or autologous bone marrow transplantation, has gr
eatly improved the survival of women with certain neoplastic diseases
such that pregnancy is a realistic option. In these times, obstetricia
ns face the task of caring for women who have used or are currently us
ing one or more potent immunosuppressive medications. The purpose of t
his article is to assess and summarize our current knowledge regarding
the use of immunosuppressives in pregnancy, focusing primarily on the
ir effects on the mother and fetus. The reader should understand, howe
ver, that most of our current knowledge in this area is derived from l
imited animal studies, case reports, and small case series. It is like
ly that pregnancy-induced immunologic changes alter both the response
and the potential adverse effects of many immunosuppressive agents. Fo
r example, pregnant women have lower peripheral CD4 lymphocyte counts,
depressed interleukin-2 production and natural killer cell function,
and increased circulating levels of complement proteins compared to no
npregnant women.(10) Both the dose and timing of drug exposure may be
important, and effects of immunosuppressive agents on immunologic inte
ractions at the critical maternal-fetal interface may be pivotal.