One of the first things that every pregnant couple needs to let go of as soon as possible is the expectation of having their baby be born on a specific day. This is just not something you can count on. When you, your provider, or an internet application attempts to calculate your due date some very big assumptions are being made.
First, that you know the exact date of your LMP – or last menstrual period. You find that date by using the first day you began bleeding on your last menstrual period. Some folks will know this without question. They’ve been trying to get pregnant, or may even be using IVF or other means of getting pregnant that really require a heavy amount of tracking in order for conception to take place within a certain timeframe.
But, remember the window for conception is a little bit bigger than you think! You can get pregnant any time from about five days before ovulation occurs right up to the actual day of ovulation. So knowing exactly when you conceived your little bundle of joy might not be as predictable as you think. And then don’t forget all the other people who, quite honestly, have no idea what their LMP is! “Umm… I think it was the 15th. Maybe?!”
The second assumption is that you have a 28-day menstrual cycle. Some of us do – but only about 10-15%. The rest have cycles that can vary anywhere from 21-35 days in length. And then even that number can vary from month to month. Life events, varying degrees of stress or illness can mean that the number of days between periods fluctuates and doesn’t always remain consistent or regular.
But what if we use ultrasound to determine the almighty due date? How accurate is that?
Well, it ends up being slightly more accurate than using the LMP calculation, but it’s not perfect, either! According to this great article from Evidence Based Birth, there’s an optimal time to receive an ultrasound to determine gestational age, and that range is between 11-14 weeks.
The most common time for a pregnant person to receive an ultrasound, however, is somewhere between 16-20 weeks. The study referenced here showed a significant decline in accuracy happening at that 20 week mark. And 3rd trimester ultrasounds are even less accurate than earlier ultrasounds and LMP.
But even if a pregnant person has an ultrasound at the optimal range of 11-14 weeks, this study found that about 68% of pregnant people gave birth + or – 11 days of their estimated due date via ultrasound! If you were a betting person, these are not good odds for putting any amount of money down that a baby will be born on a specific day.
Calculating a due date can be helpful, I guess. It allows your provider to have a guide by which to measure the growth and development of your baby in relation to your gestation. And it also allows pregnant folks and their partners to have some idea of when pregnancy will finally be over! And it can be a helpful planning tool! It lets friends know when they should send out invites to the baby shower, and it allows the Grandmas to figure out when they should be flying out to help after baby is born. It’s helpful. It is.
But, unfortunately, by the time I see couples in my classes this due date has long been cemented in their minds as “The Day The Baby Will Be Born.” As if any other date will be off somehow.
In reality, only 3-5% of babies arrive on their actual due date. If yours is one of them, I’d start playing the lottery, my friend!
You’re actually considered “due” for about 2 weeks before that due date and about 2 weeks after that due date. So, it would be wise for you to start considering your due month, rather than your due date. Why is this so important?
The exact trigger for spontaneous labor is not really well understood. But it’s widely regarded that there’s a complex interaction between the baby and the pregnant person that causes the uterus to begin contracting and labor to start.
Some ideas that have persisted over time include the following: a significant shift in the estrogen/progesterone ratio prior to labor beginning. When estrogen levels increase toward the end of pregnancy, it increases the levels of prostaglandin production which is known to assist in the ripening of the cervix. These heightened levels also increase the number of oxytocin receptors that exist on the uterus, as well as increase the contractility of the uterus overall. The baby’s adrenal glands and pituitary glands may actually play a significant role in controlling the timing of labor. The fetal production of the hormone cortisol can lead to increased levels of prostaglandin, as well increase the maturation of their lungs which in some way might trigger that babies are ready to be born.
In “normal person speak,” the hormones of the pregnant person and their baby play an important role together in signaling the start of labor. If and when it is possible, we should honor this natural, normal and physiological start to labor. It benefits both the parent and the baby – not just in pregnancy and birth, but also in their immediate postpartum experience.
Folks who get very attached to their due date as the day their baby will arrive have a couple of potential issues from the get-go. If the baby comes anytime in those two weeks prior to the due date, couples can find themselves either caught completely off-guard or risk feeling and acting as though they have had a pre-term birth. This, in turn, might cause them to parent with unnecessary caution, concern or added anxiety, when in fact – their baby was born term, just a little bit before the estimated due date.
Folks who deliver on the other side of their due date, who are already sick of being pregnant, face an even bigger challenge in my opinion. Because, let’s face it, at 38 weeks gestation most pregnant people begin to repeat this mantra daily, “Get it out of me – now!” They start counting not only the days they go past their due date, but the hours, and then the minutes and then the seconds… It’s a slow and painful kind of self-inflicted torture.
It’d be great if much earlier in pregnancy, a couple could realize the futility of trying to determine the actual date that the baby will be born and instead focus on the due month.
So try this little exercise…
Your estimated due date as determined by LMP, ultrasound or what your provider has told you is: (A)_____. The date on the calendar 14 days before this due date is: (B)_____. The date on the calendar 14 days after this due date is: (C)_____. Now you know the approximate timeline in which your baby will make their arrival, their due month.
Begin to look at your calendar in this new way. Tell everyone you know that you now understand that your baby will arrive sometime between dates B & C. Get a marker and highlight those dates on the calendar if it will help you to get rid of the idea that your baby will come on a certain and particular day. It is, and has always been, only an estimate.
And that is something you can count on.
Experienced Parents Please Share: When you were pregnant, how invested were you in your due date? Did your baby actually arrive on that date? Was your baby “early” or “late”? What would you have done differently if you’d considered your due month instead of a particular date?