As days go by, the doctor measures the height of the uterine bulge during every consultation. If growth is normal and as expected, with the correct height being reached, the week calculation for measuring the baby’s growth would be correct.
In the 12th week, the uterus starts growing out of the pelvic bones. In 16th week it raises between the naval and the pelvic bone. By the 22 to the 24th week the raise is still the naval. By the 36th week, the raise expands to the stomach and the lower portion of the diaphragm. This is the maximum it should reach. By then the circumference of the stomach reaches about 36 inches. On the penultimate 14th day, it shrinks by one inch.
Increasing height of the uterus is a good guide for the doctor. Any abnormality in it like excess height or below normal height indicates something is wrong and that immediate examination is required.
Doctors use the term LMP for calculating the delivery date. This means Last Menstrual Period. The delivery date is calculated from this date. This is called EDT i.e. Estimated Date of Delivery.