Blood type linked to risk of premature birth, study suggests

A woman’s blood group may influence her risk of premature birth, according to research examining over 74,000 maternity records.

The study found women with blood groups B and O faced higher risk of spontaneous preterm birth, while those with group A had lower risk.

Preterm birth means labour starts naturally before 37 weeks of pregnancy.

 Dr Lynne Sykes is lead researcher and clinical associate professor at Imperial College London, and consultant obstetrician at Imperial College Healthcare NHS Trust.

She said: “Although we did not establish causation, we have identified a genetic link that can influence the risk of spontaneous premature birth in women.

“This could potentially impact women in the future by identifying risk earlier in pregnancy and by offering more tailored interventions.

“While we need further research, the prospect of moving towards personalised care in this area is hugely exciting.”

Researchers analysed anonymised maternity records, including high-risk pregnancies.

They believe women with blood group A are more likely to carry higher proportions of Lactobacillus crispatus, a protective bacterium, and show less inflammation – both factors linked to healthier pregnancies.

Risk patterns varied depending on other medical factors.

For women whose only risk was previous cervical surgery, blood group B was linked to a greater chance of preterm delivery. Among women with a history of late miscarriage or prior premature birth, group O showed the highest risk.

Microbiome analysis of 596 high-risk women revealed possible biological mechanisms.

Women with blood group A were more likely to carry Lactobacillus crispatus. Groups B and O were linked to more diverse bacterial patterns.

In women with group O, this bacterial profile was directly tied to inflammation and spontaneous preterm birth.

The researchers also showed that blood group sugars are secreted into vaginal fluid and can bind to certain vaginal bacteria.

But they lacked “secretor status” data – a genetic factor affecting whether these sugars are present. About 80 per cent of people are “secretors”, while 20 per cent are not.

The findings suggest ABO blood group, routinely tested early in pregnancy, could help assess preterm birth risk when combined with other clinical factors.

The team controlled for ethnicity, which affects both blood group prevalence and preterm birth risk.

Dr Sykes said: “What excites me most is the opportunity this presents for truly personalised medicine in pregnancy, something that has been sorely lacking in our field.

“The treatments we currently offer to prevent preterm birth have barely changed in decades. This research opens the door to more targeted, biologically-informed interventions.”

A clinical trial starting this autumn, funded by March of Dimes in the US, will test whether probiotic treatment with Lactobacillus crispatus (Lactin-V) can reduce premature birth in high-risk women – and whether response varies by blood group.