For many women who plan to conceive a child at some point, 35 has been perceived as the magic age when they suddenly enter the risk group. But new research from Sweden suggests this “risk zone” begins much earlier, starting as a woman leaves her 20s.

The study, published in the journal Obstetrics and Gynecology, was conducted by investigators from Karolinska Institutet in Stockholm, Sweden.

They note that increasingly, women in the world’s wealthiest countries are giving birth at later ages, which has led to an increased risk of preterm birth, hindered growth and stillbirth.

To analyze risks among age groups of women giving birth for the first time, the researchers used data from the Swedish and Norwegian medical birth registers, yielding information on nearly 1 million women between 1990 and 2010.

They adjusted odds ratios of certain categories, including very preterm birth, moderately preterm birth, small for gestational age, low Apgar score, fetal death and neonatal death, after separating the women into four age groups:

  • 25- to 29-years-old
  • 30- to 34-years-old
  • 35- to 39-years-old
  • 40-years-old or higher.

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Though 35 has long been considered the start of the risk zone for women to have children, this recent study suggests women are at risk of complications as early as age 30.

Although the investigators say women in the age group of 30-34 have not normally been considered as a risk group, their results tell a different story.

Compared with the 25-29 age group, first-time mothers between the ages of 30 and 34 had a higher risk of having a premature birth – in weeks 22-31 – or having a stillbirth.

The team notes that other factors, such as smoking or being overweight or obese, “significantly increased” the risk of experiencing serious pregnancy complications.

“We were surprised that the risk for certain outcomes increased at such a relatively early age,” says Ulla Waldenström, professor at the Department of Women’s and Children’s Health at Karolinska Institutet.

Prof. Waldenström continues:

“For women individually, the risk is small, but for society at large there will be a significant number of ‘unnecessary’ complications with so many women having children just after 30. It would therefore be advisable to inform both women and men, even at schools, of how important age is to childbirth.”

When asked about suggestions for women over 30 who are contemplating having a baby, Prof. Waldenström told Medical News Today:

The best advice is to avoid smoking and overweight/obesity, if that is possible. I would also point at the very low risk for the individual woman. The prevalence of very preterm birth increased from 6/1000 women in a low-risk group aged 25-29 years to 10/1000 at age 30-34, and the corresponding figures for stillbirths were from 2/1000 to 4/1000.”

The researchers say they will soon assess the possible ramifications of giving birth to a second or third child in so-called advanced years in a registry based on 2.2 million women.

A recent study suggested that pregnant women who have pre-existing diabetes have a higher risk of stillbirth or infant death.