Bartholomews rule of fourths

if the uterine fundus is one-fourth of the way from the pubic symphysis to the umbilicus, the pregnancy is of two months' duration; one-half of the way, three months' duration; three-quarters of the way, four months' duration; at the umbilicus, five months' duration. The fundus then rises one-quarter of the way to the ensiform process each month until the ninth, when it sinks to the level it occupied at eight months.