Estimates in Pregnancy
A good preparation for the upcoming labor and delivery prevents life threatening risks to the mother and the baby. To have an idea when the estimated date of delivery (EDD) is, the nurse should have knowledge on the different estimates used for pregnant women. These techniques may or may not exactly point out the EDD or age of gestation, but it tries to estimate the age of pregnancy and possible date of delivery for the mother to be prepared.
Nagele’s Rule
Nagele’s rule is used to determine the EDD on the basis of the first day of the last menstrual period or LMP. To calculate the date of birth in this rule, subtract 3 months from the first day of LMP then add 7 days and change the year. For example the last menstrual period (LMP) began July 30, 2010. To determine the EDD follow the following steps:
- Subtract 3 months (June 30, May 30, April 30) = April 30, 2010
- Add 7 days then change the year = April 30 + 7 (April has 30 days only, thus, adding 7 days would make the EDD May 7) = May 7 (change the year) = May 7, 2011
Modified McDonald’s Rule
measuring the fundic height in mcdonald's rule
McDonald’s Rule or method is used to determine the age of gestation by measuring from the fundus (obtaining the fundal height) to the symphysis pubis.The distance in centimeters will determine the age of gestation from 16-38 weeks. (From Benson and Pernoll’s handbook of obstetrics and gynecology)
Johnson’s Rule
Johnson’s rule is used to estimate the weight of the fetus in grams. To determine this, a standard formula is used.
Formula: fundic height in cm – n x k
k is constant, it is always 155
n is 12 if the fetus is engaged. It is 11 if the fetus is not yet engaged.
Example:
A fundic height of 28 cm, and the fetus is not engaged.
28 cm – 11 x 155 = 17 x 155 = 2635 grams
Bartholomew’s Rule of fourths
This method estimates the age of gestation relative to the height of the fundus of the uterus above the symphysis pubis.
By 3rd lunar month (12 weeks), the fundus is slightly palpated above the above the symphysis pubis.
By the 5th lunar month (20 weeks), the fundus is palpable at the level of the umbilicus.
On the 9th lunar month, the fundus is at the level of the xiphoid process.