Fertility in the 40s: the trend and the threat
According to the 2023 National Demographic and Health Survey (NDHS), women aged 40 to 49 are the only age group in Nigeria showing an increase in fertility rates, while fertility rate declines across all younger age groups.
However, biologically, fertility naturally declines with age. According to the American College of Obstetricians and Gynecologists (ACOG), female fertility begins to decline more sharply around age 32 and drops significantly after 37, with natural conception becoming rare by the mid-40s.
The rise in 40 to 49 fertility has been attributed to the shift in the average age women get married, which is often due to their pursuit of higher education, careers, or personal growth, which eventually leads to delayed family formation.
While the fertility rate for this 40 to 49 age group is still significantly lower than 15 years ago, the current upward turn is noteworthy in a country like Nigeria where early motherhood has historically dominated.
In the mid-2000s, Nigeria's age-specific fertility rate for women aged 40 to 49 was higher than today but steadily declined over the years. The 2018 NDHS and earlier rounds showed consistent decreases across all age bands, including 40 to 49.
However, recent data from the 2023 NDHS shows moderate growth in the fertility of women aged 40-44 and 45-49.
According to Oxford Academic Research, the shift in fertility trends is being driven by the education of women and an accompanying shift in life’s purpose away from procreation
Consequently, motherhood is occurring later in life than in previous generations, a pattern aligned with the gradual rise in the average age at first marriage
Over the past decade, Nigeria has seen a steady rise in the age at which women marry for the first time. In 2014, the average stood at 19.6 years, increasing to 21.4 years by 2023. While this 1.8-year increase may seem modest, it marks a meaningful shift in societal norms around marriage and family planning, potentially contributing to the increase in childbirth among older women in Nigeria.
Globally, data shows a rising trend in the average age at which women marry, particularly in high-income countries where delayed marriage is often linked to higher levels of education and economic opportunity.
In contrast, countries like Bangladesh and Niger where child marriage remains prevalent continue to report low average ages of marriage, with little to no change over the years. This pattern is also observed in several sub-Saharan African countries, where traditional norms and limited access to education contribute to persistently early marriages.
This increase in the age of first marriage aligns closely with the rising fertility rates among women aged 40 to 49 in Nigeria, as previously noted. If marriage is being delayed until the early 20s or beyond, childbearing naturally shifts forward as well.
The Biology of Fertility and the Age Factor
This trend deserves cautious optimism. On one hand, it suggests greater autonomy among women to make reproductive choices aligned with their life goals. On the other, it raises public health considerations.
Pregnancies in the 40s carry higher health risks and demand more sophisticated maternal care. This is due to the decreasing quantity and quality of eggs. In Nigeria, where access to fertility diagnostics is limited, many women may not be aware of these biological constraints until later in life, often after several failed attempts to conceive or carry a pregnancy to term.
According to a New York Times article, while assisted reproductive technologies like in vitro fertilization (IVF) offer alternatives, their success is similarly age-dependent. CDC data shows that the likelihood of a successful pregnancy through IVF drops from 36% for women under 35 to about 6% for those over 42. In Nigeria, the high cost of IVF ranging between ₦1.3 million and ₦2 million per cycle makes it largely inaccessible for most women, especially in the absence of widespread health insurance coverage.
Pregnancy risks also increase with age. Older women are more prone to complications such as miscarriages, gestational diabetes, and pre-eclampsia. Women aged 40–44 face a one-in-three chance of miscarriage, largely due to chromosomal anomalies in ageing eggs.
In Nigeria, where prenatal screening and high-risk obstetric care remain unevenly distributed, especially in rural areas, these risks are compounded by poor access to emergency care and inadequate maternal health infrastructure.
Stillbirth risks also rise among older mothers, often exacerbated by late or missed antenatal care. Studies have linked this to conditions like high blood pressure and gestational diabetes, which become more common with age.
Thanks for reading this edition of SenorRita. It was written by Adijat Kareem.
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