Pregnancy due date calculators are only as accurate as the person using them and should be taken with a grain of salt. These are certainly not childbirth prediction devices. If you have an accurate record of when your last period was and your cycles are fairly regular; any online calculator will be able to supply you with a date. Your doctor will use essentially the same method; however, it’ll be in the form of a small cardboard wheel that requires the identical information. What this gives you, however, is an estimate rather than an actual date that your baby will be making his or her entrance into the world.
A normal, full-term pregnancy lasts anywhere from 38 to 42 weeks, or roughly 280 days from your last period. Any due date calculator you consult, whether it’s technologically advanced or the cardboard equivalent of a decoder ring from a Cracker Jack box, is going to aim for the middle, or 40 weeks, and is designed to do this basic math for you. There are women who deliver before their ‘due date’ and some that hang in there until they are a solid 42 weeks, but an astonishingly low percentage (about 5%) actually delivers on that magic date provided by the due date calculator.
At your first visit to the OB, your doctor will probably pull out the cardboard wheel and give you a date that you, no doubt, have already figured out after plugging the same numbers into every online due date calculator you could find. Many doctors will do an early ultrasound at this visit, which confirms this date based on the size of your baby, and will likely spit out a date that is either the same, or very close to the one that both, you and your doctor, came up with. Occasionally, some women are shocked when they realized they’re been pregnant for a month longer than they had thought because their last ‘period’ was actually the light spotting of implantation bleeding.
Month after month you will visit your doctor, and several things will be checked to ensure that your original due date is still on track. As long as the fetal heartbeat is strong, and your uterus is growing in proportion with the week of pregnancy you are in things should be moving along swimmingly. Between 17 and 20 weeks, you’ll get the ‘big’ ultrasound that will check on bone structure, organ systems, general fetal health, proper growth and the gender if you want to know it. If you’re paying attention, you’ll see that the due date will change by up to a week or more with each measurement they take, however, actual due dates are rarely changed at this time.
If you haven’t given birth already you may become discouraged when that magical due date comes and goes. If this is your first baby the possibility of delivering later, then that date is a bit higher but not guaranteed. In all three of my pregnancies, this author never saw a due date arrive without already holding a week old newborn in her arms. And then again, there are some women who are habitually ‘late’, giving birth as close to the 42-week mark as possible in every delivery.
Due date calculators, as it turns out, are just another fun thing to do while waiting to meet the little person living in your belly. They’ll give you a day to shoot for but in no way can predict the day your baby will be born. What it can tell you, and your doctor is what to base baby’s growth on during your entire pregnancy. Essentially, if the due date calculator says you’re due on February 17th, you can feel confident telling people that you’re due ‘mid to late February!’