Estimates of Pregnancy

References:

1. Dr. RPS Maternal and Newborn Care: A Comprehensive Guide and Source Book for Teaching and Learning, 2nd Edition, ISBN 978-971-98-2265-3, by Rosalinda Parado Salustiano (Ch. 5, pp. 99–103)
2. Lecturers (V)

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Estimated Date of Delivery/Confinement

1. Naegele’s Rule (EDC, EDD): add seven days to the first day of the last menstrual period (LMP), and subtract three months, and one year.
   • Ex: $04/10/2023+-03/07/0001=01/17/2024$
2. Mittendorf’s Rule (EDC, EDD): a method that takes into account the woman’s race and gravidity:
   • Caucasian and G1: $\text{EDC/EDD}=(\text{LMP}+15\text{ days})-3\text{ months}$
   • Non-Caucasian and G>1: $\text{EDC/EDD}=(\text{LMP}+10\text{ days})-3\text{ months}$
3. Date of Quickening ($Q$): taking into account quickening only,
   • Primigravida: $Q+4\text{ months and }20\text{ days}=\text{EDC/EDD}$
   • Multigravida: $Q+5\text{ months and }4\text{ days}=\text{EDC/EDD}$
4. Fundal Height (FH): using fundal height (measured from the top of the symphysis pubis to the palpable fundus) estimate EDC/EDD. Prior to examination, the mother needs to void.
   • FH at Symphysis Pubis: 12 weeks (3 months)
   • FH at Umbilicus: 20 to 22 weeks (5 months)
   • FH at Xiphoid Process: 36 weeks (early 9th month)

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Age of Gestation

1. LMP/Gestational Age/Menstrual Age: calculation of the duration since the last menstrual period. Ovulatory age or fertilization age is calculated from the time of ovulation or fertilization. These are two weeks shorter. LMP dating has a 95% prediction interval of ±4.65 weeks (Lee et al., 2020). Mothers may also be unsure of their last menstrual period.
2. Ultrasound: a better (Self et al., 2022) determination of gestational age; cerebellar measurement appears to be the most accurate. The American College of Obstetrician and Gynecologists, the American Institute of Ultrasound in Medicine, and the Society of Maternal-Fetal Medicine recommend first-trimester sonography as the most accurate method to establish or reaffirm gestational age.
3. McDonald’s Rule: determination of AOG based on fundal height (FH) used in the second and third trimesters. Measure the distance from the top of the symphysis pubis over the curve of the abdomen to the top of the uterine fundus using a tape measure.
   • AOG in lunar weeks: $\text{FH in cm}\times 8/7$
   • AOG in lunar months: $\text{FH in cm}\times 2/7$
4. Bartholomew’s Rule of Fours: estimates gestational age based on fundic height. Prior to examination, the mother needs to void.
   • FH at Symphysis Pubis: 3 months
   • FH between the symphysis pubis and umbilicus: 4 months
   • FH at Umbilicus: 5 months
   • FH just above umbilicus: 6 months
   • FH between the umbilicus and xiphoid process: 7 months
   • FH just below the xiphoid process: 8 months, or late 9th month due to lightening.
   • FH at Xiphoid Process: early 9th month
5. Gestational Age Calculator (Michalowska & Smialek, 2023): assessing gestational age by estimated due date (EDD).
   • $\text{LMP}=\text{EDD}-280\text{ days}$
   • $\text{Current Date}-\text{LMP}=\text{GA}$
6. Ultrasonography: measurement of the biparietal diameter. A biparietal diameter of 9.5 cm is found in a mature fetus, often obtained at the 36th week.
7. X-ray: done only at the 16th week onwards; the distal femoral ossification is present at 36 weeks, and proximotibial ossification is present at maturation.
8. Date of Quickening: felt at the 20th week.
9. Identification of FHT: at 12 weeks by Doppler.

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Fetal Dimensions

1. Estimated Fetal Weight (EFW):
   • Johnson’s Rule: utilizes fundal height to estimate fetal weight, and varies based on engagement.
     • $\text{EFW in grams}=(\text{FH}-11)\times 155$ if not engaged
     • $\text{EFW in grams}=(\text{FH}-12)\times 155$ if engaged
2. Estimated Fetal Length (EFL):
   • Haase’s Rule: utilizes gestational age to estimate the fetal length in centimeters.
     • First five months of the pregnancy: ${\text{AOG in months}}^2$
     • Second half of the pregnancy: $\text{AOG in months}\times 5$