An old mattress stops bouncing back: the filling clumps together and the springs lose their give. A woman's ovary ages in much the same way, except that instead of filling it is stiff connective tissue that proliferates, and the springs are played by the cells that support the eggs. For the first time, scientists have measured that stiffness in living women using ultrasound, and tied it to the odds of a successful round of IVF.
The study included 32 women under 33 and over 37, plus 100 women between 24 and 45 for validation. Ovarian stiffness was measured with an ultrasound technique that sends vibrations through the tissue and reads its elasticity from how fast they travel. It turned out that in women over 37 the ovary is considerably stiffer than in younger ones. At the same time, the protein collagen accumulates in the fluid around the eggs, making the tissue stiff, while connective tissue cells become activated and set off inflammation.
Until now, ovarian fibrosis in humans could not be measured without surgery, and now it can be done quickly and safely. A doctor can use this measurement to predict in advance how a woman will respond to ovarian stimulation in an IVF cycle. You cannot fix an old mattress, but you can learn to predict when it will stop springing back, and choose the right treatment strategy ahead of time.
Ovarian stiffness in women over 37 reaches values comparable to those of a cirrhotic liver (up to 40 kPa), even though the ovary is far smaller. What is more, the spread of stiffness within a single ovary is wider in older women than in younger ones, reflecting the patchy nature of fibrosis.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.