Getting pregnant at a later age is often considered a risky pregnancy as many previous studies have found that there is an increased risk of children being born preterm or with a low birth weight in women 35 years and older.
Low weight babies have higher risk of respiratory, cognitive, and neurological problems than those born with normal weight. Preterm babies suffer from an increased risk of heart defects, lung disorders, brain damage, and delayed development.
More and more women are getting pregnant at a later age especially in high income countries, making these risks very relevant.
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But according to a new study, conducted by the Max Planck Institute for Demographic Research (MPIDR) and the London School of Economics, the advanced age of mothers does not seem to be the cause for the increased birth risks.
For this study the researchers compared between-family models (comparing children born to different mothers at different ages) with within-family models (comparing children who are born to the same mother at different ages) and used Finnish population registers of 124,098 children.
The researchers analysed Finnish families with at least two children 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.
When they compared this to children born to different mothers at different ages, risks went up significantly with the age of the mother. For example, the probability of a low weight birth for a mother age 40 and above is 4.4 per cent when compared to a woman between 25 and 29 years at 2.2 per cent.
So on the whole advanced age of the mother is still a predictor for preterm deliveries and low birth weight and more likely to occur when the mother is older.
But for an individual mother, age does not seem to be the real cause of increase in birth risks but may be associated to individual circumstances in the life of the parents or behaviours that are common in older adults.
Such potential risk factors could be fertility problems which are associated with poor birth outcomes and with older maternal age, level of maternal stress and other unhealthy behaviours.
The researchers were able to isolate the effect of pure age on the risk of poor birth outcomes in children born to the same mother by excluding potentially influential factors in this analysis, as they did not vary between pregnancies of any individual woman. But they did vary between different families.
Factors that do change for the same mother from one birth to the next, such as family income and birth order could be excluded as reasons for increased risks by controlling for them statistically.
When the age of the mother was the only factor that changed in their statistical calculation, the increase in birth risks disappeared.
The researchers say that more research is needed to understand the true reasons for increase in birth risks for older women but it seems that women should not be concerned about their age as such but rather their individual circumstances and behavioural choices at that age.
Source: American Journal of Epidemiology
