A child's heart, even before birth, already listens to chemical signals from the mother. When mothers are given the hormonal drug betamethasone to help the fetus's lungs mature early, this signal can leave a lasting mark on the heart rhythm for years to come. Researchers studied 49 children aged 8 to 15: 12 received a low dose of the hormone (less than 5 grams total), 13 received a high dose, and 24 received none. During a short stress test, solving mental arithmetic problems, the children's electrocardiograms were recorded.

It turned out that children with the high dose showed a notably faster rate of heart rhythm complexity increase compared to those with the low dose. It's like comparing two runners: both are running, but one accelerates faster. Other complexity measures did not show such a difference. Interestingly, the effect appeared specifically during mental arithmetic, when the brain is actively working, not at rest. The researchers checked whether the result depended on the signal processing method and confirmed that the main indicator remained stable regardless of the approach.

These findings are like a mosaic: prenatal hormone exposure leaves two traces on the heart. One is like a shape imprint, independent of dose. The other is like a dynamic adjustment that strengthens with higher doses. These are only initial observations from a small group of children, but they hint at where to look next.