Doctors say that a blood test could detect older mothers at highest risk of stillbirth or premature births.
Pregnant women who give birth in the late 30s or 40s are more likely than others to experience complications.
Manchester University scientists now know how to predict which mothers are most at risk.
Mothers-to-be over the age of 35 tended to have lower levels of placental growth factor — made naturally when the placenta is healthy,
However, they also had more antioxidant capacity — a measure which shows if cells in the organ are degenerating or inflamed.
Professor Alex Heazell, the lead author, stated that “Mothers over 35” are becoming more common in many countries.
“Unfortunately, having a baby later in life has been associated with higher pregnancy risk.
“We already know that pregnancy complications are often linked to changes in oxidative stresses and inflammation, as we saw in this study.”
“But for the first-time here, we discovered they were also present in older moms, which could be damaging to the placenta and may explain why older mothers are at greater risk.”
He said, “If we measure these biomarkers, along with demographic data and clinical variables that affect pregnancy risk, it could help us predict an individual’s risk of an adverse pregnancy outcome at a later age.
Professor Heazell said that further research on the biomarkers was necessary before they could create a risk calculator.
Researchers from the University of Manchester discovered two markers that can be detected in a blood test taken at week 28, which is up to 74% accurate in predicting a woman’s likelihood of having problems during her birth.
According to data from the Office for National Statistics, pregnancy rates in England and Wales among women aged 30 or older have been increasing at an accelerated rate over the past decade. Rates for women aged 20 or younger have been declining or flattening.
Women are becoming more likely to wait until later in their lives to have children. In the UK, 25% of babies are born to women over 35.
Studies have shown that people are more likely to have children later in their lives if they have a strong focus on financial and career concerns.
However, the risk of stillbirth, premature births and infants being admitted to intensive medical care is up to twice as high for older mothers.
Researchers took blood samples from 527 women – based at six hospitals across the UK – at weeks 28 and 36 of pregnancy between March 2012 and October 2014.
Some 158 women were in 20s, 212 in their 30s, and 157 in their 40s.
To determine the impact of age on stillbirth and premature birth, samples were taken from young and old mothers with similar characteristics.
They also determined the risk of the participants’ babies being admitted to intensive care or having a low Apgar score – a test that determines how well a baby copes immediately after birth.
Their study, published in the journal BMC Pregnancy Childbirth, found placental growth factor was the best way of predicting a negative pregnancy outcome, with 74 per cent accuracy, while antioxidant capacity gave accurate predictions 69 per cent of the time.
Analysis of blood samples showed that antioxidant capacity was higher in older women than normal. However, placental growth factors were lower at week 36.
Women who gave birth to healthy babies were half as likely as those who had problems with their pregnancy.
The risk of adverse pregnancy outcomes for women over 35 who smoked prior to and during pregnancy was four times higher than that for women who had not smoked. It was twice the risk for ex-smokers.
Jane Brewin, chief executive of pregnancy charity Tommy’s, which funded the study, said it could help doctors spot vulnerable mothers and ‘avoid unnecessary medical treatment for those with lower risks’.
She added: ‘The tendency to start families later in life now means there’s a real and urgent need for better ways to predict how a mother’s age will affect her pregnancy health.
‘Mums over 35 face higher risks of their babies being born too early, too small, or even stillborn – but if we can identify those in need of help, we can prevent these problems and save babies’ lives.’