About 45% of people with Down Syndrome have a single palm crease in their hand instead of 2. This is because they did not hold their fist clenched tight in the womb due to hypotonia.
I wasn’t aware of this before I did some reading whilst pregnant. As far as I can tell it doesn’t cause any issues and is just another possible lovely little feature our babies might be born with. Frida doesn’t have a single palm crease, but does have a sandal toe gap between her big toe and second toe on both feet (see website logo for print of her foot at about 4 weeks old). It’s super cute and will make the annoying first few wears of flip flops each year less uncomfortable for her!
When I posted this on Facebook, three friends commented that either they, or family members without Down Syndrome had a single palm crease on one or both hands, so it cannot be all that uncommon across the general population as a whole!