Oral polio vaccination during pregnancy: lack of impact on fetal development and perinatal outcome.

Prompted by a nascent epidemic of poliomyelitis in Finland, a mass vaccination program with live oral poliovirus vaccine (OPV) was implemented in February and March 1985. The final rate of coverage was approximately 94%. Pregnant women were included, and a cohort study was launched to evaluate any harmful effects of OPV on the developing embryo. All records of births to mothers who were pregnant during the period of vaccination and whose infants were delivered at the three major hospitals in the Helsinki area were reviewed. Within the study cohort, mothers were grouped into three categories according to their trimester of pregnancy during the program. In addition, two reference cohorts were evaluated; these cohorts consisted of infants delivered at the same hospitals during the second half of 1984 and of 1986, respectively. Each of the three categories in the study cohort included approximately 3,000 children, while each reference cohort included approximately 6,000 children. Data were analyzed on the rate of intrauterine growth and the prevalences of stillbirth, neonatal death, congenital malformation, premature birth, perinatal infection, and neurological aberration. No differences were documented among the study and reference cohorts or among the three categories within the study cohort. Thus, under the conditions described here, the inclusion of pregnant women in programs of mass vaccination with OPV appears to be safe.