A patch that measures oestrogen and progesterone in sweat could give wearers insight into their reproductive changes. This may be particularly helpful when predicting ovulation if they are trying to become pregnant.
The patch “has the potential to be less invasive than blood tests and sonograms [for gauging ovulation], and to provide more useful information than currently available wearables”, says at the NYU Grossman School of Medicine in New York, who wasn’t involved in the research.
Reproductive hormones, such as oestrogen and progesterone, regulate the menstrual cycle. For instance, high levels of oestrogen cause a surge in another hormone, luteinising hormone, that leads to ovulation. Progesterone prepares the lining of the uterus for a fertilised egg to implant and grow.
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Existing fertility trackers generally rely on signals such as body temperature, which rises after ovulation, or a series of blood or urine tests to assess hormone levels. More accurate tests include transvaginal ultrasound, which tracks the growth of ovarian follicles that will release an egg and helps determine whether ovulation has occurred. However, this is invasive, requires a clinic visit and only provides a snapshot of someone’s reproductive status.
In 2023, at the California Institute of Technology and his colleagues demonstrated that , the primary type of oestrogen produced in ovaries, in sweat. Now, they have developed a patch that also measures progesterone. “Monitoring [oestradiol and progesterone] together could potentially provide a more complete picture of the hormonal trajectory before and after ovulation, rather than a single event,” says Gao.
The patch, which uses a mild electrical current to induce sweating, contains a sensor with two DNA molecules engineered to bind to either oestradiol or progesterone. Each molecule then generates a distinct electrical signal. This gives an estimated level of both hormones, which is transmitted to a smartphone app.
Detecting hormones in sweat is difficult because the composition of the liquid varies. To get around this, the researchers added a dried buffer to the sensor that is rehydrated by sweat, bringing the sample’s pH and salt concentration into a consistent range. “You can think of it as standardising the sweat before we measure the hormones,” says Gao.
The researchers tested the patch – which requires about 9 microlitres of sweat and takes 90 minutes to produce a reading – on nine women. Some of these women were of reproductive age, while the others were postmenopausal.
The team found that the hormone levels measured by the patch closely tracked those from blood tests, with correlations of 0.83 for oestradiol and 0.93 for progesterone. A score of 1 would mean the two measurements matched perfectly.
In another part of the experiment, the researchers tested the patch on three women – one of reproductive age, one who was perimenopausal and one who was postmenopausal – over 28 days, .
The changes in hormone levels detected by the patch broadly matched those seen in the women’s blood samples and what would be expected for their ages. For instance, the patch worn by the woman of reproductive age showed the expected oestradiol and progesterone fluctuations across the 28 days, while the patch worn by the postmenopausal participant showed consistently low levels of these hormones.
The next step is to test the patch on a larger group, and to see how reliably hormone levels in sweat track those in blood across different ages and reproductive stages, says Gao. The team also plans to compare the patch against established ovulation measures, such as urine tests, he says. We need to know whether the patch can predict ovulation early enough to be useful, given that hormonal changes vary between people and over time, says Goddard.
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