How babies are affected by their mother’s age

Giving birth to a child after 40 is becoming more and more common – but it can entail an increased risk to the child, researchers say. A new study based on registry data from over 300,000 births in Sweden shows that children of older mothers are more often born prematurely or with complications.

‘We could see that for babies born in Sweden, serious complications are rare, regardless of the mother’s age,’ says Sofia Voss, lead author of the paper. ‘But we also found that children of older mothers have a higher risk of stillbirth, premature birth, low birth weight relative to length of pregnancy, and low blood sugar compared to babies born to mothers aged 35–39 years. The study showed that the highest risks of all were to babies born to mothers 45 years and older.’

In Sweden, 4.8% of mothers were 40 years of age or older in 2022. Previous research has shown that older mothers differ from younger mothers in several respects such as having a higher BMI, a higher proportion having utilised assisted reproductive technology, an increased risk of certain diseases during pregnancy, and a higher proportion of births via Caesarean section. With this in mind, the researchers in the current study wanted to investigate how the mother’s age affected the health of her newborn baby.

The study, which is published in Acta Pedriatica and was carried out by researchers from Uppsala University and Linköping University, looked at data from Sweden’s National Medical Birth Register.

A total of 312,221 children born to women over 34 years of age in the period 2010–2022 were included in the study, excluding twin births. The babies were divided into three groups according to their mother’s age: 35–39 years, 40–44 years, and 45 years and older. The researchers were particularly interested in how the health of the child at birth was affected when their mother was older than 39 years. The children born to mothers aged 35–39 thus served as a reference group.

Stillbirth is uncommon in Sweden, but occurred in 0.83% of pregnancies in women who were 45 years or older. This can be compared to a rate of 0.42% in women aged 35–39 years.

Concerning premature birth, 4.8% of these cases occurred in the group of mothers aged 35–39. Among women aged 40 to 44, the corresponding figure rose to 6.1%, and among women aged 45 or older, 8.4% of their babies were born prematurely.

Previous studies have mainly compared babies born to young mothers with those born to older mothers. In the present study, the researchers were interested in getting a more detailed picture of the distribution of risk among the older mothers.

‘By comparing different ranges of advanced age when giving birth, the study can also contribute to better, and better targeted, information for women planning future pregnancies. As the share of older mothers rises, our study can help to target screening and interventions to where they will have the most benefit. But it’s also important to inform the public so that they can make informed choices,’ says Sofia Voss.