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Parents’ fertility may influence child’s asthma risk

Lengthy time to conception and fertility treatment may affect child’s asthma risk

Ingrid Torjesen

Wednesday, 05 December 2018

Children whose parents take more than a year to get pregnant and who use fertility treatment may be at heightened risk of developing asthma, suggests a study* published online in the journal Thorax.

The risk of asthma also seems to rise in line with the number of previous miscarriages early in the mother’s pregnancy, suggesting that common factors underlying poorer fertility and recurrent miscarriages might be influential, the authors propose.

Previous research suggests that children conceived with the aid of fertility treatment (assisted reproductive technologies- ART) may be more prone to asthma, but it is not clear whether it’s the ART procedures themselves or factors associated with subfertility that might be behind this heightened risk.

To try and find out, researchers linked birth and prescription data from national Norwegian health registries (involving 474,402 children born between 1998 and 2009) and from the Norwegian Mother and Child Cohort Study (75,797 children).

The data included information on fertility treatment; time to conception; number and timing of any previous miscarriages; and potentially influential factors, such as maternal age, asthma, smoking during, and weight before, pregnancy. Childhood asthma was defined as use of asthma drugs in the preceding 12 months when the child was seven years old.

Just over 4% of children in the registries group (20,189) and mother and child study (3229) had asthma.

Children in the registries group had more risk factors for asthma than those in the mother and child study: they were more likely to have been born early or small; and to have younger mothers, who smoked and had asthma themselves. But children in either group who had been conceived with the aid of fertility treatment were up to 42% more likely to have asthma.

When children born using fertility treatment were compared with those whose parents had spontaneously conceived but had taken more than 12 months to do so, they were 22% more likely to have asthma.

This suggests that poorer fertility doesn’t by itself completely explain the observed heightened asthma risk among children conceived with the aid of fertility treatment, and that aspects of ART itself may have a role, say the researchers.

The number of previous miscarriages was also associated with an incrementally heightened risk of asthma, rising from 7% for one, to 24% for three or more, although this was only observed for miscarriage during the first 12 weeks of pregnancy.

Several procedures involved in ART might affect the embryo and natural course of foetal development: for example, the drugs used to induce ovulation and maintain the pregnancy; the freezing and thawing of fertilised embryos; the hormonal environment; and embryo manipulation, the researchers said, and the immune system might also have a role.

“We propose that common immunological mechanisms might plausibly underlie the increased risk of asthma we observed both among children of mothers who suffer from subfertility and miscarriages, since immunological mechanisms contribute both to problems conceiving and repeat pregnancy losses,” they said.

Dr Jane Stewart, chair of British Fertility Society, and consultant in reproductive medicine and gynaecology, Newcastle Hospitals NHS Foundation Trust, said: “Whilst this study raises some interesting questions, there are many variables involved in both infertility and the development of asthma. This is an observational study and, as the authors state, a direct link cannot be shown between infertility, assisted reproduction and asthma. Much more investigation would be required to establish any causal link.”

*Magnus MC, Karlstad Ø, Parr CL, et al. Maternal history of miscarriages and measures of fertility in relation to childhood asthma. Thorax Published Online First: 04 December 2018. doi: 10.1136/thoraxjnl-2018-211886

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