Because the majority of women and their OBGYNs/midwives do not know when ovulation occurs, a method has been established to provide an estimated due date. A doctor/midwife counts back 3 months from the last menstrual period (LMP) and adds a year and a week to that date. wisegeek.com
If a mother is not sure of her LMP, then an ultrasound is used to determine the estimated date of birth. This estimation is based on the size of the fetus. Estimated due dates are... well...estimations at best, yet so many doctors treat EDDs as "do or die".
The truth of the matter is pregnancy lasts for 266 days or 38 weeks from conception. Due date calculations are based upon a 28 day menstrual cycle. In reality, a woman's cycle can range from 28 to 40 days. Lending further into a potential erroneous due date. Now, having your due date estimated is not a bad thing in and of itself, if it was actually treated as predicted due date. Normally, such is not the case. Inductions and cesareans are insisted upon, if you go past your "predicted" date, even though your baby is showing no signs of distress.
I learned just how off such predictors can be. While pregnant with my 4th baby, my midwife referred me to a clinic for a routine ultrasound. The doctor took measurements of baby and told us we were expecting a boy. At the end of the session, he informs us that based upon his measurements our son was due July 20th.(we never asked him to determine our due date, we just wanted to make sure there was one baby in there!) At that point, I was 7 months along (this took place in June) and I had determined my due date to be August 15, based upon the date of ovulation, but he was pretty insistent that July 20th was the EDD. My midwife said she had a due date of July 27th or so.
I did the worse thing possible, I believed him! I believed the doctor who had never met me before in my life, who had no history or knowledge of my cycle as I did. By the end of July, we figured out that the doctor AND midwife was wrong! Even more, my son was born August 20th, a FULL month after the doctor's EDD. Now, I'm sure, you can appreciate what the ramifications would have been, if I went along with the dates of my doctor and midwife. There would be no way a doctor would let me go "past my date" without some serious intervention. By the way, my beautiful son was perfectly healthy...and HUGE! He was 9lb 11oz. 22 inches long, that's why he measured so big in June. And to this day he is built like a linebacker and stands eye to eye with his older brother.
I cannot help but wonder how many premature births, or babies born with complications are related to estimated due dates. If mothers do not know or understand how their cycle works, then it is up to a medical professional to determine that. Medical professionals who do not have the same passion, commitment and love that a mother has for her child. Medical professionals who are more inclined towards policies, charts, and avoidance of lawsuits. No one loves your baby more than you do, that's why fear is such a powerful force that drives a mother to consent to procedures that carry risks and dangers without FULL knowledge of what it entails. And that's what I'm referring to knowledge, to know and understand your body. Undoubtedly, knowledge is the power a loving mom can have to protect her unborn child.
I learned how to predict ovulation and menstruation and the different hormones a woman has at different times of the month, through this wonderful book called "Taking Charge of Your Fertility" by Toni Weschler, MPH. Every woman needs to read this book. Now, I'm not promoting natural family planning as something everyone must do...everyone is free to live their lives as they see fit. However, the knowledge a woman should have of her cycle is a must...after all it could save lives, or at least prevent lives from being born too early.
What can you do if you are unsure of your ovulation date? Ask your doctor about his/her opinions on EDDs. Find out if they are flexible on going "past it" if your baby is thriving and well in the womb. If not, you may want to find a doctor that is suitable to your baby's needs. If your EDD is predicted based upon an ultrasound, I warn you, do tread with caution in regards to a given EDD. Babies come in all shapes and sizes. Sizes and charts can be erroneous when it comes to YOUR baby's size. Especially if your doctor insists on interventions upon passing your "due" date, when baby is showing signs of health and wellness.
You can quote these facts found on wisegeek.com to your healthcare provider:
10% deliver on their EDDs
1/2 deliver within a week of their EDDs
90% deliver within 2 weeks of their EDDs
I cannot end this post with a shout out to midwives. I love them! They provide a much needed relief to women who have mishandled by the medical society. However, not all midwives are created equal. Some of them can be just as medically minded towards birth as doctors. Like a pair of jeans, you need find one that fits.