The "reproductive timeline" refers to a timeframe in a woman's life when she is physiologically capable of conceiving and giving birth to children. Generally, a woman's fertility period begins during puberty, at the onset of menstruation, and continues until menopause. Even as a fetus, a woman's ovaries have already completed their development. A woman is born with all the oocytes she will ever have, i.e. approximately one million eggs in her ovaries.
As a woman ages, the number of eggs gradually decreases. By puberty, a woman may have around 300,000 to 400,000 eggs. During the menstrual cycle, only one egg matures and is released each month, while the rest naturally diminish and disappear. This process means a woman's fertility is somewhat predetermined and gradually declines over time. Around the age of 46-50, a woman's menstrual cycle becomes irregular and shortened, indicating the onset of menopause. When the number of remaining follicles in the ovaries falls below a certain threshold, ovulation and menstruation cease, signifying the end of a woman's fertility.
The ideal childbearing years: 20 to 34
The medical community generally recognises the age range of 20-34 as the ideal period for fertility. Women within this age group tend to have better egg quality and quantity, resulting in higher pregnancy success rates. Healthy women within this range have an 80-90% chance of natural conception within a year. Additionally, the body has better regenerative capabilities during younger years, and the physical burden of pregnancy and childbirth is usually lower.
Risks of early and late pregnancy
If a woman becomes pregnant too early, her reproductive organs and pelvis may not have fully matured, which can have negative implications for both the mother and the baby's health. It may increase the risk of complications, difficulties during childbirth, and the possibility of certain complications or long-term effects. Conversely, delaying pregnancy, especially after the age of 35, increases the chances of chromosomal abnormalities in the eggs, leading to miscarriages or fetal abnormalities. There is also an increased risk of complications during pregnancy and childbirth, such as gestational diabetes, hypertension, weakened uterine contractions, prolonged labour, postpartum bleeding, and a higher likelihood of experiencing difficult labour.
What counts as advanced maternal age?
Typically, the medical community considers women aged 35 and above as having an advanced maternal age. As women age, their ovarian function declines, hormone secretion decreases, and the quality of eggs significantly diminishes. After the age of 35, a woman's fertility starts to decline rapidly, and by the age of 45, the chances of natural conception become extremely low. Advanced maternal age also increases the risk of chromosomal abnormalities (such as Down syndrome) and the likelihood of miscarriage or abnormal pregnancies. Research indicates that the rate of chromosomal abnormalities in the eggs of 40-year-old women is over 50%. Additionally, advanced maternal age raises the chances of pregnancy complications such as gestational diabetes and hypertension.
Considerations for family planning
It's important to note that the concept of an "optimal" age for fertility is merely a statistical reference and does not mean that conceiving at other ages is inappropriate or impossible. The definition of advanced maternal age is not absolute. Each woman's physiological and personal circumstances are unique, and some women can still successfully conceive and have healthy children even at older ages. On the other hand, some women may face fertility challenges during their reproductive years. Government statistical data shows a rising median age at first marriage for women, increasing from 26.2 years old in 1991 to 30.6 years old in 2021. The trend of delayed marriage has shortened women's reproductive window. It is crucial for women who plan to have children to consider early life planning and strive to achieve their fertility goals in the best physical and mental condition. For older women or those experiencing fertility difficulties, assisted reproductive technologies such as intrauterine insemination (IUI) or in vitro fertilisation (IVF) may be options to consider, and it is important to have discussions with their partners in advance.
Reference
- Sharma, R., Biedenharn, K. R., Fedor, J. M., & Agarwal, A. (2013). Lifestyle factors and reproductive health: taking control of your fertility. Reproductive Biology and Endocrinology, 11(1), 66. https://doi.org/10.1186/1477-7827-11-66
- ACOG. (2020, October). Having a Baby After Age 35: How Aging Affects Fertility and Pregnancy. Www.acog.org. https://www.acog.org/womens-health/faqs/having-a-baby-after-age-35-how-aging-affects-fertility-and-pregnancy
- Glick, I., Kadish, E., & Rottenstreich, M. (2021). Management of pregnancy in women of advanced maternal age: Improving outcomes for mother and baby. International Journal of Women's Health, Volume 13(13), 751–759. https://doi.org/10.2147/ijwh.s283216
- Thomas, C., Cavazza, T., & Schuh, M. (2021). Aneuploidy in human eggs: contributions of the meiotic spindle. Biochemical Society Transactions, 49(1), 107–118. https://doi.org/10.1042/BST20200043
