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 Gillian Goddard at the NYU Grossman School of Medicine in New York, who wasn’t involved in the research.
Our fertility window could be extended by making ovaries softer 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.
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, Wei Gao at the California Institute of Technology and his colleagues demonstrated that a wearable patch could detect levels of oestradiol, the primary type of oestrogen produced in ovaries, in sweat. Now, they have developed a patch that also measures progesterone. 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. 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.
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