We are in the early phase of a period when the increased numbers of women born during the 1947 to 1965 baby boom are entering their later child-bearing years. They are also part of a generation of women who are increasingly delaying childbirth until their 30s. These two factors will likely increase the proportion of total births accounted for by this 35- to 49-year age group by 72 per cent, from 5.9 per cent in 1982 to 8.6 per cent by the turn of the century. There are important and specific risks related to pregnancies for older women as compared to younger women. It is likely that a woman's ability to conceive declines steadily to where it has been estimated that 34 to 46 per cent of women age 35 and older are unable to become pregnant. Hypertension, preeclampsia, and diabetes mellitus are not only more common but seem to carry an even greater risk for older women, resulting more frequently in fetal demise. Although there are conflicting findings, older women seem to have more babies weighing under 2,500 gm and more over 4,000 gm. It appears that there are more problems with abnormal labor patterns and a definite higher incidence of cesarean section. The literature seems to support the finding of high incidences of late pregnancy bleeding from placenta previa and abruptio placenta. Many of those factors contribute to a several-fold increase in maternal mortality for older compared to younger pregnant women. The fetus, likewise, is at greater risk. There appears to be a greater risk for spontaneous abortion, although the magnitude of the risk is unclear because of the potential confounding from gravidity, birth order, and reduced fecundity. The stillbirth rate seems to double by the late 30s and increases to 3- to 4-fold by the mid-40s. The neonatal mortality rate seems to have a mild association with maternal age. Chromosome abnormalities, especially trisomies 13, 18, and 21, and sex chromosome aneuploidies, increase exponentially with maternal age starting in the 30s, reaching levels of 1.4 per cent at age 35, 1.9 per cent at 40, and 8.9 per cent at 45, according to amniocentesis data. Some of those contribute to the higher stillbirth rate resulting in a slightly smaller incidence of chromosome abnormalities in newborns. Overall, the literature supports the finding that women and their offspring experience significant increased problems as maternal age progresses through the mid-30s and beyond.(ABSTRACT TRUNCATED AT 400 WORDS)