The fundus is the upper portion of the uterus,  opposite from the cervix.

Fundal height, measured from the top of the pubic bone, is routinely measured in pregnancy to determine growth rates. If the measurement is smaller or larger than what would be expected for gestational age, it can be a crude indicator of an abnormality (for example, a breech or sideways presentation, twins, or a placental issue), requiring further tests such as ultrasound to determine the exact nature of the problem, if any.

The female reproductive system. Public Domain

The female reproductive system. Public Domain