Pregnancies that require a little help from your friendly gynecologist can complicate using a due date calculator because of a few factors, even if you know your exact conception date. What If I’ve Had IVF or Was Otherwise Medically Assisted? That said, while knowing gestational age is a huge help in predicting when your baby will be done cooking, it’s still just an estimate, and your baby may come before or after the provided date.
Ideally this occurs at or before 13.85 weeks of gestation. Are Ultrasounds the Most Accurate Method?Īccording to ACOG (the American College of Obstetrics and Gynecology), the most accurate way to establish or confirm gestational age is an ultrasound where precise measurements are taken of the embryo or fetus. Studies suggest it is twice as accurate as Naegel’s Rule, but again, all due dates are a rough estimate of when the baby will be here, rather than a hard and fast rule. The Mittendorf-Williams rule predicts the average due date to be 288 days from your LMP, and uses 16 factors that may have an influence, like age, medical history, and ethicity to name a few. Just like any due date calculator, this one isn’t exactly perfect since it makes the assumption that you have a 28-day cycle, but it’s a fairly good place to start.
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There are a few schools of thought about how to get the most accurate due date, but the most common method, Naegele’s Rule, is made by counting out 280 days from the start of your last menstrual period. A due date calculator uses these numbers and gives you a rough estimate that doesn’t take into account any other factors that can influence your due date.įortunately, this is just one calculation method, with several others that can produce more accurate estimates. But for those who have longer or shorter luteal phases, conception can happen several days in either direction of this window, moving the due date accordingly. This is your window of opportunity, and is the time frame where fertilization generally occurs. But if you’re a ways out from that appointment and want to get a general idea, a due date calculator can help! How a Due Date Calculator WorksĪssuming your cycle is 28 days, that means your luteal phase - the time after ovulation, where an egg travels down the fallopian tube chancing an encounter with a sperm - typically happens around day 12-14 of your cycle. Of course even not knowing any of these things, your medical practitioner should be able to give you a pretty good idea of how far along you are either by performing a first trimester ultrasound, or a blood test at your first prenatal appointment. If you’re carrying a single embryo, or if there are twins (or triplets!) in there First day of your last menstrual period When it comes to calculating your due date, there are a few key factors that will help give you an idea of when the big day might be.
Naturally one of the first things you’re going to want to do - after washing your hands - is figure out when this little babe is going to make their grand entrance. In fact, only 6% of women deliver on their due date, Cackovic said.Okay, so you got your positive pregnancy test (insert whatever emotion you are currently feeling here). Once you go past about five or six days, then you have to start considering that your dates really may be off." How reliable is my due date?Įven once your doctor has established a due date, there's no guarantee that your baby will come that day. "If it's all within a week, it's consistent. "Often we get a due date based on the last menstrual period and then do a sonogram and there's a discrepancy we have to address," Auguste added. (And why I probably shouldn't be taking my second "due date" very seriously.)Īs much as technology has improved, this is all still an imperfect science. "Pretty much all pregnancies are equal at that stage."Īs a woman's pregnancy progresses, fetuses develop at different rates, which is why an estimated due date from an ultrasound measurement during the second trimester is less accurate.
"The reason why is there's very little variation that can be detected in a measurement from that time," he said.
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