Background

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Since 2000, the fertility rate in Canada has been on the rise, reversing a trend of declining fertility that began in the early 1990s. The total fertility rate in 2005 was 1.54 children per woman, which was a significant increase from the low rate of 1.48 set in 2000 (Statistics Canada, 2007). This rise in the fertility rate has been primarily attributed to increased fertility among Canadian women in their thirties (Statistics Canada, 2007).

Many women are also postponing childbearing until later ages. Over the past 20 years, Canada has seen a substantial increase in the proportion of first births occurring among women age 35 and older. While only 4% of first births in 1987 occurred among women aged 35 and up, by 2005 the rate had nearly tripled at 11% (Figure 1). Over this same period, the proportion of first births occurring among women in their early thirties also increased, from 15% in 1987 to 26% in 2005.

The trend towards older motherhood is not unique to Canada. The mean age of women having their first child in the United States rose from 21.4 in 1970 to 24.9 in 2000 (Matthews & Hamilton, 2002). Nevertheless, Canadian women are more likely to have their first child in their thirties than their American counterparts. In 2004, more than a third (35%) of births to Canadian women in their thirties were first births, while the proportion in the United States was only 27% (Statistics Canada, 2006).

Risks of advanced maternal age

Advanced maternal age is associated with a number of risks. Older mothers are at increased risk of fetal loss such as miscarriage or stillbirth (de La Rochebrochard & Thonneau, 2002; Fretts, Schmittdiel, McLean, Usher, & Goldman, 1995; Nybo Andersen, Wohlfahrt, Christens, Olsen, & Melbye, 2000), decreased ability to conceive (Broekmans, Knauff, te Velde, Macklon, & Fauser, 2007; Gougeon, 2005; Rizzi, Rossina, & Colombo, 2005) and complications of pregnancy (Astolfi & Zonta, 2002; MacNab, Macdonald, & Tuk, 1997; Prysak, Lorenz, & Kisly, 1995; Ziadeh & Yahaya, 2001). There are also increased risks of birth defects (Reefhuis & Honein, 2004) and birth complications (Astolfi & Zonta, 2002; MacNab et al., 1997; Prysak et al., 1995; Ziadeh & Yahaya, 2001). However, less is known about the relationship between advanced maternal age and children's development.

Among studies that have examined maternal age and children's outcomes, the majority have focused on the health and development of children of teenaged mothers (Levine, Pollack, & Comfort, 2001; Pogarsky, Thornberry, & Lizotte, 2006; Spieker, Larson, Lewis, Keller, & Gilchrist, 2006). Findings from such studies suggest that, in early childhood, children of teenaged mothers tend to have higher levels of behaviour problems, while cognitive and academic problems become pronounced as they enter adolescence (Brooks-Gunn & Furstenberg, 1986). Furthermore, children of teenaged mothers are more likely than other youth to become teenaged parents themselves (SmithBattle & Leonard, 2006; SmithBattle, 2007). In most such studies, maternal age is characterized as teenaged or not teenaged, and is not examined as a continuum.

Among the studies that have examined advanced maternal age, Fergusson and Woodward (1999) found that the risks of youth's educational underachievement, involvement in crime, substance misuse and mental health problems at age 18 decreased with increasing maternal age. This study also found that, while increased maternal age was associated with more nurturing and stable home environments, controlling for such factors did not fully account for the effect of maternal age on children's later outcomes. However, Fergusson and Woodward did not distinguish between maternal age at the birth of a specific child (which was the measure in the Fergusson and Woodward study) and maternal age at first birth. Other studies have shown that a child's behavioural and cognitive development is better predicted by mother's age at first birth than age at the child's birth (Lopez Turley, 2003). This distinction is important because early age at first childbirth may have an impact on the life opportunities available to young mothers (SmithBattle, 2007), thereby affecting the well-being and development of all subsequent children, regardless of the woman's age at future births.