Usual positioning of the developing fetus with the back curved forward, head bent forward, and limbs drawn in towards the body.
Note: This position arises from the natural positioning of the embryo as the
germ layers develop.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 722 (https://doi.org/10.1515/pac-2015-1202)