Thickening on the margin of the yolk sac of a fetus during pregnancy.
Note: Appearance of the fetal pole is used as the earliest sign of a baby in
ultrasound examination.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 755 (https://doi.org/10.1515/pac-2015-1202)