Genetic variants controlling length of pregnancy identifed

Genetic variants linked to the timing of the onset of labour have been identified, and suggest a tug-of-war between the effects of genes expressed by the mother and those by the fetus.

A genome-wide association study of 190,000 women of European ancestry, who went into labour spontaneously, without medical intervention investigated whether there was an association between timing of birth and genetic variants. The paper published in Nature Genetics revealed 24 variants associated with timing of birth, and six closely related loci associated with pre-term delivery, which is the single biggest driver of neonatal death globally. Fifteen of these acted through the maternal genome, two through the fetal genome and seven through both.

First author, Dr Pol Solé-Navais, from the University of Gothenburg, Sweden explained: 'What we see is that there might be a conflict between the genomes of the woman and unborn child respectively when it comes to the duration of pregnancy. Genetically, the woman's genes favour earlier onset of labour to expel the child, for her own survival, while those of the unborn child favour extension of the pregnancy to gain weight. So, they reach a kind of compromise deal'.

Despite the impact of the timing of birth on infant health, the understanding of how genetics controls the timing of birth is largely unresolved.

The leader of this study, Professor Bo Jacobsson, professor of obstetrics and gynaecology at Sahlgrenska Academy, University of Gothenburg said 'The results have given us more routes to understanding how labour is initiated, both at full term and in premature labour. In samples, we were able to identify numerous previously undiscovered genetic variants associated with the timing of parturition, and these provide unmatched insights into the underlying biological mechanisms.'

Variants identified that were associated with timing of birth were found to be correlated with genes known to to be associated with age at first birth, first menstrual period and menopause, as well as hormone levels, endometriosis, polycystic ovary syndrome and miscarriage.

Women who conceive using IVF are more likely to experience pre-term labour and give birth to babies with lower birth weights, though the reasons are unclear. Previous research has suggested that this is not a side-effect of treatment, but rather the mothers' overall health including underlying conditions that could be linked to fertility (see BioNews 1128). Black women have a four-fold increased risk of pre-term delivery following fertility treatment (see BioNews 1164).