In fact, due date estimates during the third trimester can be off by as much as 21 to 30 days since fetal development rates vary significantly after the first trimester. Estimates made during the third trimester screening are the least accurate.

Your due date was based on your last menstrual period, but you have a history of irregular periodsĪfter your second trimester, your doctor is unlikely to change your due date.

(For instance, if your doctor believes you’re 16 weeks along, but your AFP levels don’t match standard 16-week levels, it may be the case that your pregnancy was inaccurately dated.)

There are discrepancies between your due date and your levels of alpha-fetoprotein (AFP)-a protein produced by your growing baby that increases and decreases during certain weeks of pregnancy/strong>.

the size of uterus) doesn’t align with standard growth charts

Your baby is noticeably smaller or larger than “the average,” based on her estimated age.

For instance, your due date may change if: This decrease in accuracy is due to the fact that fetuses develop at significantly different rates after about 8 weeks.ĭuring routine ultrasounds in your first and second trimester, your doctor may change your due date based on what they see.

In fact, gestational age assessments that take place between weeks 14 and 21 of pregnancy have an accuracy of between 7 to 10 days (as opposed to the 5 to 7 days of early pregnancy ultrasounds). While your doctor can also take measurements during your second trimester to estimate your baby’s gestational age (and therefore estimate your due date), these estimates are less accurate. With the estimated gestational age, your doctor can then estimate your baby’s due date. This method can also provide a more accurate estimation if your menstrual cycle doesn’t follow a typical 28-day cycle.ĭuring an early ultrasound (which typically takes place between weeks 6 and 8 of your pregnancy), a ultrasound technician can measure the length of your baby’s crown-rump length, and other biometric variables to determine your baby’s gestational age within 5 to 7 days of accuracy. You can still find out your estimated due date by having an ultrasound scan at your doctor’s office. If keeping track of dates and schedules isn’t your thing, don’t worry. For an IVF 5-day transfer date – If you opted to have your embryo transfer take place on day 5 of embryo growth, your doctor can calculate your due date by adding 261 days to the transfer date.For an IVF 3-day transfer date – If your embryo transfer took place on day 3 of embryo growth, your doctor can calculate your pregnancy due date by adding 263 days to your IVF transfer date.the day your fertilized eggs were implanted onto your uterine wall). If you’re one of 33% of Americans who’ve turned to fertility treatments or know someone that has, such as IVF, to conceive, your doctor can easily determine your expected due date by using your IVF transfer date (i.e. or-for our IVF mamas-to-be-by using the date of your IVF transfer. Methods Your Doctor Can Use to Calculate Your Due DateĪside from the methods utilized in this pregnancy calculator, you can also learn your due date by asking your doctor to perform an ultrasound scan. (You add 266 days because the average pregnancy is 280 days, minus the 14 days of your cycle). Ovulation typically occurs on day 14 of a 28-day menstrual cycle, so adding 266 days to your conception date will give you your baby’s due date. The date of conception is essentially the date you ovulated, which can be used to calculate your estimated due date. If fertilization doesn’t occur within this time period, the egg dissolves. This is the part of your menstrual cycle when a mature egg leaves your ovary in the hopes of becoming fertilized in the 12 to 24 hours after release. If you were tracking your cycle you may know your ovulation date and use this date of conception to estimate your due date. So although you won’t be seeing your period for a while, Aunt Flo can actually help you discover your estimated pregnancy due date. You can also count back 3 calendar months from the first day of your last period, then add 1 year and 7 days to that date.īaby center has copy about why it’s 40 weeks + ovulation that could be good to add something similar Find the date that marks the first day of your last period.On average, pregnancies last around 40 weeks, or 280 days. Using the first day of your last menstrual period is the most common method for calculating your due date. Take a look below at how each of these methods works. Our due date calculator gives you the option of two methods to determine when your baby will arrive: the date of your last menstrual period or your conception date, also known as ovulation date. She is the owner of The Genesis Resort for Birth and an Assistant Professor of Nursing at James Madison University.

Heather has 15 years of women’s health and obstetrics experience.

Birth date calculator conception