Health problems 'more common for babies with older fathers'

Thursday November 1 2018

"Health risk to babies of men over 45, major study warns," The Daily Telegraph reports.

A study of more than 40 million births in the US found babies born to men aged 45 or older were more likely to be born prematurely, have a low birth weight and need intensive care after birth than babies with younger fathers.

The increase in risk was small, but because more men and women are having children later in life, the researchers say men should be aware that delaying fatherhood is not risk-free.

Women have been warned for many years about the potential risks of delaying motherhood, but there's been less research looking at the impact of men's age on their children's health.

Researchers believe the increase in risk may be because of changes to the sperm of older men, which could affect the growth of the embryo.

But we can't be sure that the men's age was the only factor influencing the outcomes.

While the researchers took the age of the mothers into account, the health and lifestyle of both parents could still have had an influence.

Following a healthy lifestyle is indeed important for men thinking about trying for a baby.

Cutting down on alcohol, avoiding recreational drugs and not smoking are keys ways men can keep their sperm healthy.

Where did the story come from?

The researchers who carried out the study were from Stanford University School of Medicine in the US.

The study received no specific funding.

It was published in the peer-reviewed British Medical Journal on an open access basis, so it's free to read online.

The Mail Online repeatedly said that older age raised the risk of "birth defects".

They didn't define what they meant by this, but the term is often used to refer to abnormalities in the newborn, such as a hole in the heart. The study didn't actually look at newborn abnormalities.

The Guardian ran a more balanced story, which stressed that the risk to individuals was small and factors other than fathers' ages might have been involved.

The Daily Telegraph accurately reported the results, but didn't discuss any of the potential limitations of the study.

What kind of research was this?

This was a cohort study.

Researchers wanted to see how paternal age related to a range of possible health outcomes for newborn babies and the mother during pregnancy.

Cohort studies are good for spotting links between factors (in this study, between mens' ages and pregnancy and birth outcomes), but can't show that one directly causes another.

Other factors, such as the age of the woman, or the man's lifestyle, could be involved.

What did the research involve?

Researchers accessed birth certificates and registrations from the US National Center for Health Statistics, which gave them information about all live births reported in the US between 2007 and 2016, a total of 40,429,905.

They categorised the births according to the father's age:

  • younger than 25
  • 25 to 34
  • 35 to 44
  • 45 to 54
  • 55 or older

They looked at the number of births in these age categories that resulted in:

  • premature birth (less than 37 weeks)
  • low birth weight (less than 2.5kg)
  • low Apgar score (a test of the overall health of a newborn baby measured 5 minutes after birth, from 0 to 10; scores less than 8 are considered low)
  • need for admission to a neonatal intensive care unit
  • need for antibiotics
  • seizures
  • gestational diabetes (diabetes in pregnancy) in the mother
  • pre-eclampsia or eclampsia (complications from maternal high blood pressure in pregnancy)

The researchers used the age group 25 to 34 as a reference point, and looked to see if risks for other age groups were higher or lower in comparison.

They adjusted their figures to account for potential confounding factors, such as the year of birth, maternal age, parental ethnicity and education, antenatal visits attended, tobacco use and marital status.

What were the basic results ?

Compared with fathers aged 25 to 34 years, babies born to men aged 45 to 54 had:

  • a 14% increased chance of being born prematurely (odds ratio [OR] 1.14, 95% confidence interval [CI] 1.13 to 1.15), representing 14.2% of babies born to men in this age group versus 10.4% of younger fathers
  • a 14% increased chance of having a low birth weight (OR 1.14, 95% CI 1.12 to 1.15), representing 9.9% of babies born to men in this age group versus 7.0% of younger fathers
  • a 14% increased chance of needing intensive care (OR 1.14, 95% CI 1.13 to 1.16), representing 8.2% of babies born to men in this age group versus 6.0% of younger fathers
  • a 18% increased chance of having a seizure, although the numbers for this result were so small the results could have come about by chance (accounting for less than 0.05% of all fathers, OR 1.18, 95% CI 0.97 to 1.44)
  • a 4% increased chance of having a low Apgar score (3.9% versus 3.4% with younger fathers; OR 1.04, 95% CI 1.02 to 1.06); older fathers 55 or over had a higher risk (4.4% versus 3.4%; OR 1.14, 95% CI 1.08 to 1.2)

Women pregnant by men aged 45 or over had a 28% increased chance of gestational diabetes (OR 1.28, 95% CI 1.27 to 1.30), affecting 9.6%, compared with 5.3% pregnant by younger fathers.

How did the researchers interpret the results?

The researchers said: "While it is important to note that the absolute risk of advancing paternal age on adverse perinatal conditions remains modest, our findings emphasise the need to further investigate the public health implications of increasing paternal age."

They also said "preconception counselling guidelines" might need to change to warn men of the possible risks of delaying fatherhood.

Conclusion

Headlines like the one in the Mail Online, saying that "men should start a family before they are 35 to avoid their children having birth defects", are not just scaremongering, but wrong.

The study found a small increase in some risks to babies born to fathers over 45, and didn't look at birth abnormalities.

The study's main strength is its size and the amount of information available to researchers. But it has some limitations.

Because it's an observational study, it can't show that paternal age directly caused conditions such as prematurity.

It's hard to disentangle the possible effects of confounding from the mothers' age and from the health and lifestyle factors of both parents.

Even though the researchers tried to take account of these factors, they may not have been able to do so completely.

As 1 expert commented in a linked editorial in the BMJ, age may be less of an issue than lifestyle.

Some studies have shown that older fathers may have less healthy lifestyles than younger fathers – for example, drinking more alcohol, and being more likely to be overweight or have chronic diseases. This could have influenced the results.

The risks to individual babies shown in the study aren't high, and they don't increase greatly with parental age. The absolute difference in numbers was fairly small, typically only a few percent different.

While ideally couples would have children while they're both healthy and likely to have the best chance of fertility, personal factors mean this isn't always possible.

We can't be sure that fathers' age directly accounts for the slight increase in risk, so it's important that expectant older parents aren't too concerned about this research.

Analysis by Bazian
Edited by NHS Website