Due Dates are Rarely Accurate - So Why Do They Matter?

July 13, 2021
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First things first, if you’ve just found out you’re pregnant — Congratulations!

No doubt, one of your first questions is: when will I meet my little one?

The easiest way to estimate your due date is with a pregnancy calculator. All you need to do is enter a few bits of info and it will quickly calculate your estimated due date (emphasis on ‘estimated’).

Why due dates are rarely accurate

While it seems like figuring out your due date should be easy (nine months, right?), the truth is only about 5% of babies arrive on their expected due dates. And in fact, only 35% will arrive the week of their estimated due date.

Why so few on-time arrivals? Turns out, most moms-to-be aren’t even aware they’re pregnant until their first missed period. While for some that may be just a few days after conception, in some cases, it can actually be up to five weeks.

Even if you know the exact date you conceived, other factors will influence when the big day will arrive. Studies have found that some babies simply develop faster in utero.

Other studies suggest that snug quarters, especially in women under 5’3”, will contribute to an early arrival. On the flipside, babies of tall moms-to-be (5’6”+) may linger a little longer in the spacious quarters of a bigger womb.

Kind of makes you wonder why due dates even matter.

The imperfect — but important — science of your due date

While rarely precise, due dates are important in tracking your baby’s development and planning for their arrival.

According to Kimberly Congden, program manager of Lactation Services and Parent Education at Baystate Medical Center in Springfield, “Due dates are vital to tracking the progress of a pregnancy. Many of the tests your OB provider orders and the recommendations they make are based on the week of a pregnancy, rather than a specific day. A due date, even if it’s off by a week, allows them to assess a baby’s development and determine if other tests are warranted, or, later in the pregnancy, they may intervene and induce labor or, in some cases, take steps to delay it.”

Congden also notes the importance of making an appointment with your midwife or OB/GYN to begin prenatal care as soon as you learn you’re pregnant. She notes, “Early prenatal care is important to getting your pregnancy off to a good start and keeping you and your baby healthy throughout the experience. Signing up to take childbirth classes is also recommended by the 4th month of pregnancy. These classes prepare you and your partner no matter when your little one chooses to arrive.”

Support for Parents

Learning that you’re pregnant is just the start of your parenting journey. Baystate Health’s Parent Education program provides a variety of resources for every stage of pregnancy, childbirth, delivery, and beyond. Classes are available virtually, as well as tours of our birth centers in Greenfield and Springfield.

Once you know your due date, we recommend signing up for our email newsletter. This email provides information based on your stage of pregnancy (and your child’s age up to three years).


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