The Lowdown On Due Dates
I have chosen to leave this 2020 image here to reiterate the message of this blog. A reminder that clinging rigidly to dates and attempting to control all outcomes creates pain.
Silly season is here. A time of year when, deep down, we know we simply want (and need) to slow down and connect with our loved ones, yet everything around us is ringing in the message that we need to read our lists and check them twice to make sure we have everything wrapped up and the turkey cooked by the 25th.
If you’re pregnant and planning a hospital birth, you’re probably feeling the pressure even more. While there’s nothing like advent calendars everywhere to make you feel like you’re on a countdown, it’a pressure that is not exclusive to Christmas. It plays in the minds of most expectant mothers who are “due” around the time of any major religious or public holidays. In all truth, it plays in the mind of any woman from the minute her obstetrician spins the wheel on the date predictor and says, “You’re due on….”
The advice I always give my clients, however, is this:
You don’t have a due date, you have a due month.
Telling friends and family the month, rather than a precise date will take a whole lot of unnecessary pressure off you in the final trimester as you nest in and tune in to your body’s signals.
The reality is that the little wheel of fortune that your doctor spins is far from being a crystal ball. In fact, the idea that it is a scientifically sound tool for predicting birth is… well… more than slightly off the mark.
How is your due date calculated?
Since the 1800s, practitioners have been trained to use Naegele’s Rule when calculating a due date. The rule assumes a gestational age of 280 days at childbirth. They take the date of the start of a woman’s last menstrual period (LMP), add a year, subtract three months and add seven days. Today, women will usually also have a dating scan which measures the baby and gestational sac. This can at times result in a new date being given. In 2016 ACOG also created the EDD app which aims to address discrepancies between dating scan dates and LMP date. Each one of these techniques exists for practice “management”. Are you frowning a little like I am typing this?
Given the overwhelming need of most women today to have things diarised and dotted and schedules scheduled, this date becomes cemented in the minds of most mothers-to-be. The result is not only self-imposed pressure to perform and have that baby out by set date, but also pressure from others who know the date and can’t help but asking “Is it here yet!!!!?” and “Are you STILL pregnant!?” when the big day arrives.
But there’s a very important word, however, is usually left off when that due date is given.
ESTIMATED (n) an approximate calculation or judgement of the value, number, quantity, or extent of something.
The date is precisely not precise. It’s an estimation, and studies today reveal that the variation in dates is significant.
In a study published in the journal Human Reproduction in August 2013, scientists who were able to track precise time of ovulation and implantation discovered that the average length of pregnancies varied by as much as 5 weeks… 37 days! The conclusion of the research: “That natural variability may be greater than we have previously thought, and if that is true, clinicians may want to keep that in mind when trying to decide whether to intervene on a pregnancy."
Flaws in the figures
Naegele’s Rule was based on the assumption that a lunar month is 28 days. All you moon goddesses out there will know that it is in fact 29 days 12 hours and 44 minutes (and even this varies slightly throughout the year). A quick calculation reveals that this mean gestation can (in a healthy mother with a healthy, functioning placenta) safely be around 290 days as opposed to 280… 42 weeks.
Naegele’s Rule also assumes that all women have a 28 day cycle and ovulate on day 14. This is certainly not the case. Cycles can range from 24 to 35 days, which means that ovulation can occur APPROXIMATELY anywhere between day 10 and 23.
The current predictor also fails to take into consideration the reality that every woman is unique and that the variables go far beyond length of menstrual cycle. A study by Harvard’s department of Epidemiology revealed that maternal parity, age, and race also has an influence on the length of human gestation. Multiparous women, women aged < 19 or > 34 years, and women of colour were found to have shorter gestations than primiparous women, women aged 19 to 34 years, or Caucasian women.
All this taken into consideration, “due” dates can vary from 37 to 42 weeks. This variation means that an unnecessary induction (ie an induction chosen purely on date rather than any indications that a baby is in distress, not thriving or that the placenta has indeed started to lose function) could result in a baby being born a month early. A significant amount of time when one considers lung and brain development that occurs in the final month of gestation. Growing research on the maternal and infant microbiome also suggests that changes in a mother in the final weeks may also be significant in ensuring healthy seeding of the infant microbiome, thus impacting future health.
Despite this evidence, it is widely known that, when public holidays loom, calls for induction and intervention become all too common.
Factors that should not affect your gestation period
Your obstetrician’s holiday plans
Your family’s holiday plans
Don’t be pushed to hurry. Everyone else’s mince pies can wait for your little pudding. Surround yourself with people who honour the blessing of a birth that happens in its own sacred time. Remember, Mary had no idea when she was due. And it turned out just perfectly.
Sources:
Length of human pregnancies can vary naturally by as much as five weeks - https://www.sciencedaily.com/releases/2013/08/130806203327.htm Predictors of Human Gestation Length - https://www.ncbi.nlm.nih.gov/pubmed/8438913 Practice Management: The Pregnancy Wheel Reinvented — Tap, Instead of Spin, Your Way to a Date https://www.acog.org/About-ACOG/ACOG-Departments/ACOG-Rounds/February-2016/Estimated-Due-Date-Calculator?IsMobileSet=false