Age and fertility

Advanced maternal age

The developed world has seen a gradual increase in child-bearing age of women throughout the last three decades. The term ‘advanced maternal age' is used to define women age 35 or older at the time of delivery.

Fertility, ovarian ageing, and chromosomal abnormalities

Although there are many factors that contribute to decreased fer­tility, a significant factor in age-associated infertility appears to be ovarian ageing and the diminishing ovarian follicle count. There appears to be less contribution from the uterine endometrium, as this has the capacity to maintain a pregnancy throughout a woman's reproductive years.

When a girl enters puberty, there are approximately 300,000­500,000 oocytes available in the ovaries, however only approximately 400-500 eventually undergo ovulation (1) (Figure 6.1). Due to a bi­exponential decline in the ovarian pool of follicles with advancing age, there is an accelerated loss of follicles from the age of 35 (2). For example, a woman at age 38 will have only approximately 25,000 fol­licles available, with a further decline to approximately 15,000 at age 40, and by 51, only a few hundred remain (2, 3).

Advanced maternal age increases the baseline risk of chromo­somal abnormalities and Down syndrome (trisomy 21) (4, 5). The risk of having a baby with Down syndrome rises with maternal age, essentially doubling from approximately 1 in 1000 at age 30 to ap­proximately 1 in 400 at age 35 (6). This risk continues to climb to approximately 1 in 30 at the maternal age of 45 years (6) (Table 6.1).

Biopanic

Although the average age of women conceiving is increasing, there remains a considerable societal pressure for women of this age group to achieve success in areas of life such as occupation, financial sta­bility, and relationships. Many women find themselves feeling pres­sure to balance the desire to achieve successes in their profession, while expecting to conceive spontaneously, which has led to an emerging public health effect of ‘biopanic'. As can be seen in Figure 6.2, the largest increase in conception rates has occurred in women age 35 and older, which unfortunately coincides with the same age at which there is an accelerated loss of follicles, and subsequent re­duction in fertility (7).

Fertility techniques

This sense of ‘biopanic', with the conflicting desire to achieve spontaneous conception has led to increased rates of women older than 35 years undergoing advanced fertility techniques, including in vitro fertilization and donor insemination, as can be seen in Figure 6.3 (8).

Embryo cryopreservation is the process in which eggs are re­trieved from a woman's ovaries, followed by fertilization with sperm either from a partner or donor, and then stored at freezing temper­atures for a period of time.

Oocyte cryopreservation is the process in which eggs are retrieved from a woman's ovaries and stored at freezing temperatures for a period of time. While embryo cryopreservation is a technique of fertility preservation that has been used for decades, oocyte cryo­preservation is a relatively new technique.

Societal changes have led to new developments and unique uses of fertility techniques for women in the workforce. Companies such as Apple and Facebook have been reported to offer their female em­ployees fully-compensated oocyte cryopreservation (9). As can be seen in Figure 6.4, there is an increase in the percentage of women starting fertility treatments after age 35 since 1997 to 2009. However, in 2013, there appears to be a bimodal distribution of women's age less than 35 and greater than 35 at the time of starting treatment, which is likely contributed in part to women in the workforce starting this process earlier in their careers.