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8th June 2017
10:25am BST
The average age of women becoming mums has been rising for decades in high income countries. A number of scientific studies have found that among mothers 35 or older, there is an increased risk that their babies will be born preterm (less than 37 weeks of pregnancy) or with low birth weight (less than 5lbs).
Low birth weight children have more respiratory, cognitive, and neurological problems than those born with normal weight. Meanwhile, preterm babies have elevated risks of heart defects, lung disorders, brain damage, and delayed development. However, new research that has just been published in the American Journal of Epidemiology, suggests that advanced maternal age per se does not seem to be causing the increase in birth risks.
The study, conducted by Mikko Myrskylä, director of the Max Planck Institute for Demographic Research and Alice Goisis from the London School of Economics, looked at thousands of Finnish families where at least two children were born to the same mother between 1987 and 2000. They found that within the same family the advancing age of the mother did not increase the risk of poor birth outcomes.
In contrast, when they compared children born to different mothers at different ages, risks went up notably with the age of the mother. For example, the probability of a low weight birth for a mother age 40 and above is twice as high (4.4 percent) as compared to a woman between 25 and 29 (2.2 percent).
Goisis says that, on the whole, preterm deliveries and low birth weights still occur more often when the mother is older, but are more likely to be based on individual factors:
"A doctor who only knows the age of a pregnant woman can still use her age to predict the birth risk. However, for the individual mother, age is not the real cause of the increase in birth risks. The true reasons are more likely to be individual circumstances in the life of the parents or behaviours that are more common in older adults."The authors say that potential individual risk factors could include fertility problems, which are associated both with the risk of poor birth outcomes and with an older maternal age at birth, levels of maternal stress, and unhealthy behaviours. By looking at children born to the same mother, the researchers were able to isolate the effect of pure age on the risk of poor birth outcomes. Myrskylä notes that when only the age of the mother changed in the statistical calculations, the increase in birth risks disappeared:
"Our findings suggest that women should not be concerned about their age per se, when considering to have a child. It seems that individual life circumstances and behavioural choices are more important than age."
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