Estimated Due Date {EDD} Inaccuracies

estiamted due date esali birth

Due Date Inaccuracies and Methods of Guessing Baby's Birth Time

First things first, EDD actually doesn't mean "Due Date" it means Estimated Date of Delivery.  That's just as disgusting though, really, all the numbers just point to a big jumbled mess of misinformation.  However, an estimate is sometimes very helpful because it not only allows a birth team to guess when they might be needed, but it also helps a provider compare gestational development with other babies of the same age to increase their ability of ruling out complications.  Ultimately, though, what happens more often than not is the provider simply uses it as a tool to schedule interventions and make their life more manageable.  Having 200 prenatal clients per year for a care provider attending hospital births is a pretty normal number, and the better they're able to schedule means the more sleep they get and ultimately they can provide better care from their perspective.  This doesn't always play out well for mothers and babies, especially in the long term.

Average Length of Pregnancy

In historical cultures, pregnancy was known to last 10 lunar months and was really not specific.  A woman would look at the full or new moon cycle closest to conception and count 10 cycles and she would know her baby would be born by then.  She wasn't picking a date, just figuring out a birth season.

OK... pause.

This is actually really important.  Most people believe the moon has a 4 week, or 28 day cycle.  10 months * 28 days = 280 days.  280 days / 7 days of the week = 40 weeks.  OK, that makes sense, right.  Most modern people have been led to believe a pregnancy is full term at 40 weeks.  But in fact, this is wrong.  The moon's cycle is actually 29.5 days.  If we're going to get calculators out and start trying to pinpoint, let's at least get the beginning numbers correct.  So, if the moon has a 29.5 day cycle, that actually means it should be calculated to last 295 days (10 * 29.5 = 295) and 295 days / 7 days in a week = 42+ weeks.

Is it any wonder most women birth closer to 42 weeks?

However there are so many factors that play into modern pregnancy lengths, physical and emotional health being the biggest contributor, that average lengths of pregnancy vary by 5 weeks according to some reviews, and are averaging 266 days from ovulation (this is not the same as the amount of time from LMP, we'll get to this below). There is yet other information that says primips (primiparous women - or those carrying their first babies) averaged 288 days and multips (multiparous women or women gestating a subsequent child) averaged 283 days.  We must consider the cultures these estimates are coming from, too, as most civilized and modern cultures have drastically different activity levels and emotional health from tribal cultures.

Imagine if your 37 week old baby was induced and he really wouldn't have been ready for another 5 weeks...  whew, that's a big difference!

Methods of Calculating the Estimated Due Date {EDD}

What is incredibly frustrating is that the estimated due date isn't calculated from conception; it is calculated from the first day of the last menstrual period (LMP).  In a woman with a 28 day cycle this is about 2 weeks prior to conception.  In a woman with a longer cycle this could be 2 to 4 weeks prior to conception... or who really knows if the woman's cycles are really kind of all over the place.  While we're not going to get into the cycle lengths here, this is a huge difference when we're talking gestational development and interventions for "overdue" babies.  Keep in mind, if the mother is doing well and baby is doing well, a date is just a date... an estimate... a guess.

A few historical methods of calculating the due date include:

Naegele's Rule (for a 28 day cycle - but used modernly for women of all cycle lengths)

  • Determine the first day of your Last Menstrual Period
  • Add 1 year
  • Subtract 3 months
  • Add 7 days

I get confused every single time I read that description...  but it equals out to about 280 days (from LMP)

Wood's Method (for variable cycle lengths)

  • Determine the first day of your LMP
  • Primips: add 1 year, subtract 2 months & 14 days (now if you have a varied cycle, add the difference between your actual cycle length and 28 days) = estimated due date
  • Multips: add 1 year, subtract 2 months & 18 days (now if you have a varied cycle, add the difference between your actual cycle length and 28 days) = estimated due date

Are you just as confused as the first?  Why are we still trying to pinpoint a date???

Lunar Method

Is this an actual method?  Historically, yes.

  • Determine your first symptoms of pregnancy, your date of conception or ovulation or IVF
  • Determine the full moon prior and count to the 10th full moon following
  • (If you only know your LMP, use the full moon after LMP)

Makes much more sense.  So much easier to remember.  Lunaception is historically a common occurrence because artificial lights and adequate activity levels would have made women's cycles match more closely with the moon cycles.  Some modern trends are starting to focus on family planning using this "method" that aligns so closely with nature.  With 5 weeks of variation in births actually occurring around an estimated due date, you're going to get just as accurate counting moon cycles and have a much better sense of not freaking out over interventions.  You may learn a lot about your body and your cycle (and overall health) in the process when you start noticing how your body reacts to changes in the environment.

Gestational Age vs Fetal Age

Remember that most modern methods of calculating the estimated due date focus on LMP.  Even many "alternative" or traditional or midwifery providers still use modern EDD methods for scheduling and development purposes.  Your gestational age is calculated from LMP.  When you say "I'm 20 weeks," you're referring to gestational age.  Fetal age is from the date of conception, and for all intents and purposes is guessed to be 2 weeks after your LMP.  This is still focusing on a 28 day perfect cycle with ovulation occurring 14 days after LMP.  Either way, if you're 20 weeks from LMP or 20 weeks from conception, all babies develop differently.

Your Pregnancy Length is Unique

You cannot determine when this baby is going to be ready.  You cannot determine when your body for this pregnancy will be ready.  Everything is an estimate, so never get caught up in numbers.  It does not matter if you are 36 + 3 days.  Not at all.  The more you try to pinpoint these numbers, the more stress you're going to feel when 40 weeks comes and goes, or you're measuring 42 weeks when you're only 38 weeks.  It doesn't matter.  What matters is how you feel and how you live.

Eat well.  Move well.  Be well.

If your friends and family, and provider, just can't get on board with this method of thinking - just send them to this website and turn off your screens.  Take a walk in the woods, go swimming, connect with nature and free your mind.  Focus on you and not a number.  Your baby will likely never stay in those rigid lines we like to imagine we can create.  Now is the first step to learning your unique child and your unique self.  #lifelessons