The concept of a due date was first established in the early 1800s. At that time, Franz Carl Naegele officially declared that pregnancy was full term at 10 lunar months past the first day of a last normal menstrual period. These days, due dates are determined in much the same way, with the exception that 40 weeks is considered full term.
Unsurprisingly, a lot of stock seems to be put on the Due Date. However, the calculations that lead us to a date can often be deceiving. For instance, several factors seem to play into a finding a correct calculation. Even measurements in the first trimester are capable of having an error bar of plus or minus five days by the time the pregnancy has reached the second trimester, and plus or minus 22 days by the third! There are also suggestions that whether a woman is on her first or subsequent pregnancy will affect the EDD, as will ethnicity. Studies show that multipara women had a shorter gestational length than first-time moms, as did African-American woman when compared to Caucasians.
In addition to the above, ultra-sound determined due dates aren’t as accurate as we have been led to believe. Since many practitioners may not appreciate the limitations of technology, they readily change due dates by a few days if they detect a discrepancy. If a woman has been told she will be induced if she goes past a certain date, changing a due date by even a day or two is no trivial alteration! Since the accuracy of a due date is not an exact science, induction should not be taken lightly.
Going “Over-due”
Since due dates are easily miscalculated, it’s not possible to tell for certain if a woman is over-due from the date. Other factors need to be taken into account before induction is considered, so as not to risk a low-birth weight or under-developed lungs in the baby. Calculation methods are actually a generalization derived from the median duration of pregnancy of women at the time the method was established.
So, not only have we conceded that certain motherly characteristics have an affect on these medians, but we must also take into account the unique variations of the individual as well. Since not all women menstruate on the average 28 days cycle, this can alter the accuracy of an EDD as well. I myself know that at the time of conception for my second pregnancy, my cycle was longer than 28 days. I had one due date that was “normal”, and another four days later in case my cycle played a factor. Guess what? She came three days after the second date! According to a normal calculator, she was 8 days late. Each mom and each baby have a different internal clock, and may require more or less gestation time than a similar duo would.
A recent report in the OB/GYN Journal (Dec ’01) states that eliminating the concept of a due date, “may be helpful to all involved.” When you stop insisting on a specific date for a decision to induce or not, you can start relying on the wisdom inside you. Listening to your body instead of checking the calendar may give you more insight to the birthday than you can imagine. Focusing on external “danger signs”, such as a passing due date, may distract you from noticing important inner cues.
For my first pregnancy, I knew the exact date of conception and still I went over my due date by ten days. Had I been under the care of an OB, I may have received pressure to induce labor. As it turns out, I delivered a very healthy, alert 6 lb. 9 oz. girl on what I believe was her true due date, and consequently threw the notion that I delivered “past due” out the window. Since I don’t hold stock in the exact date anymore, for my second pregnancy I adopted a practice of telling curious people a due week, and not due day.
If you are overdue, ask yourself if you are feeling anxious because you don’t want to be pregnant anymore, or because you truly think something may be wrong. Considering the fact that only 5% of babies come on their EDD, expecting a baby to be done gestating, and inducing a woman for not delivering “on time” is truly one of the more absurd practices of our culture.
Try the Wood’s Method:
Carol Wood is a Yale nurse-midwifery professor who came up with a method to calculate the due date, that takes into account individual variations in the menstrual cycle as well as number of previous pregnancies.
1. Add 1 year to the first day of the last menstrual period, then
For first-time mothers, subtract 2 months and 2 weeks
For multi-paras, subtract 2 months and 2.5 weeks (18 days)
2. Add or subtract the number of days her cycle varies from 28 days
*1st-time mothers with 28 days cycles: LMP + 12 months – 2 months, 14 days = EDD
*Multiparas with 28-day cycles: LMP + 12 months – 2 months, 18 days = EDD
*Cycles longer than 28 days: EDD from above calc. + (actual length of cycle – 28 days) = EDD
*Cycles shorter than 28 days: EDD – (28 days – actual length of cycle) = EDD
Don’t forget to visit the Pregnancy Due In Groups forum to chat with others that share your “Due Month”!