When did I conceive?
Question
I cannot exactly remember the first day of my last period before I got pregnant, but I am guessing it is roughly around the last 2 weeks of July. My baby was born after completion of 40 weeks exactly on 27 April. Can you please let me now what day did I conceive?
Answer
Last Updated: July 17, 2013
While you cannot pinpoint the exact day of ovulation, and therefore conception, with your fertility signs, the temperature pattern in your pregnancy cycle gives you the most accurate way to estimate your baby’s due date, and a clue to the approximate date of conception. Using the rule developed by Dr. Konald A. Prem when he was professor of Obstetrics and Gynecology at the University of Minnesota School of Medicine, your Estimated Date of Childbirth (EDC) is determined as follows:
EDC = First day of overall thermal shift minus 7 days plus 9 months.
1. Identify the first day of your upward thermal shift pattern.
2. Subtract 7 days.
3. Add 9 months.
The result is your Estimated Date of Childbirth (EDC) by the Prem Rule.
However, no formula can be completely accurate, including the Naegle Rule generally used by doctors, which estimates the EDC using the date of your last menstrual cycle and assumes ovulation occurring around Day 14.
In a small study of 26 deliveries conducted by the Couple to Couple League, all babies were born within 12 days before and 9 days after the Prem EDC. So even using this more finely tuned method, there is a wide range of “normal” delivery dates. This uncertainty extends to calculating a probable date of conception based on actual delivery date.
We would note that if your doctor gave you an April 27 due date using the Naegle Rule, his or her estimation of your last menstrual cycle as that it probably began around July 20. As teachers of the Sympto-Thermal Method of NFP, we would simply add that your date of conception is best determined by reference to your temperature record.
The Gronskys
EDC = First day of overall thermal shift minus 7 days plus 9 months.
1. Identify the first day of your upward thermal shift pattern.
2. Subtract 7 days.
3. Add 9 months.
The result is your Estimated Date of Childbirth (EDC) by the Prem Rule.
However, no formula can be completely accurate, including the Naegle Rule generally used by doctors, which estimates the EDC using the date of your last menstrual cycle and assumes ovulation occurring around Day 14.
In a small study of 26 deliveries conducted by the Couple to Couple League, all babies were born within 12 days before and 9 days after the Prem EDC. So even using this more finely tuned method, there is a wide range of “normal” delivery dates. This uncertainty extends to calculating a probable date of conception based on actual delivery date.
We would note that if your doctor gave you an April 27 due date using the Naegle Rule, his or her estimation of your last menstrual cycle as that it probably began around July 20. As teachers of the Sympto-Thermal Method of NFP, we would simply add that your date of conception is best determined by reference to your temperature record.
The Gronskys
Answered By:
Andrea and Ron Gronsky
Andrea and Ron Gronsky, PhD, Professional Members of CANFP,now retired, taught the Sympto Thermal Method through the Couple to Couple League, in the Oakland Region.
