Strap that tracks heart rate in pregnancy may predict premature births

Wearing a wrist-strap heart rate tracker during pregnancy may help doctors predict who is at risk of premature labour.

In a previous study, Shon Rowan at West Virginia University and his colleagues recruited 18 women to wear heart-tracking wrist straps from the brand WHOOP throughout their pregnancies.

They all delivered at full term, with their tracker data revealing a distinct decline in heart rate variability – the fluctuation in the time intervals between heartbeats – during the first 33 weeks of pregnancy, followed by a steady increase up to birth.

Curious as to whether the same pattern occurs in those who deliver prematurely, Rowan teamed up with Emily Capodilupo at WHOOP in Boston, Massachusetts, for a bigger study. The pair and their colleagues analysed tracker data provided by 241 pregnant people, aged between 23 and 47 years old, in the US and 15 other countries. It isn’t known if this data included that from transgender men.

All the participants were pregnant with a single child, born between March 2021 and October 2022. Collectively, they provided more than 24,000 heart rate variability recordings.

As in the previous study, those who delivered at full term had a clear heart rate variability switch at about 33 weeks gestation, an average of seven weeks before delivery.

However, for the 8.7 per cent who delivered prematurely, heart rate variability patterns were far less consistent, says Rowan. Their switch from a decrease to an increase in this variability occurred at different periods during the pregnancy, but, as with those who delivered at full term, it still appeared to occur an average of about seven weeks before going into labour, albeit prematurely.

The devices might one day identify pregnancies that require closer monitoring or could benefit from the administration of drugs such as steroids, which help with fetal lung development, says Rowan.

They could also be especially useful for those living in remote areas, so they can plan to stay near hospitals that offer specialised care, he says.

“If we’re able to monitor some parts of their health remotely, such as with WHOOP trackers, and we start to see that inflection [in heart rate variability], then maybe we can be a little more proactive,” says Rowan.