The third trimester is the least accurate time to date a pregnancy. In the second trimester, an ultrasound is less accurate and your doctor probably won’t adjust your date unless the estimates vary by more than two weeks. This is most likely to occur in the first trimester, especially if the date estimated by the ultrasound differs by more than one week from the date estimated by your doctor based on your LMP. Your doctor may change your due date based on the ultrasound measurement. Generally, your doctor orders an ultrasound to determine the gestational age of your baby when there’s a history of irregular periods, when the date of your LMP is uncertain, or when conception occurred despite oral contraceptive use.Īn ultrasound allows your doctor to measure the crown-rump length (CRL) - the length of the fetus from one end to the other.ĭuring the first trimester, this measurement provides the most accurate estimation for the age of the baby. Your doctor may change your due date if your fetus is significantly smaller or larger than the average fetus at your particular stage of pregnancy. What does it mean if my doctor changes my due date? Some pregnancy wheels may allow you to enter the date of conception - which occurs within 72 hours of ovulation - instead of the date of your LMP. Subtract 14 days to find your adjusted LMP date (November 8).Īfter you calculate your adjusted LMP date, simply mark it on the pregnancy wheel and then look at the date where the line crosses.Once you have a general idea of when you ovulated, you can use an adjusted LMP to find your due date with a pregnancy wheel.įor example, if your menstrual cycle is usually 35 days long and the first day of your LMP was November 1: If your cycle is 35 days long, for example, then you probably ovulated on day 21. This is the time from ovulation to the next menstrual period. The second half of a woman’s menstrual cycle always lasts for 14 days. In these cases, a pregnancy wheel can still be used, but some simple calculations are necessary. Some women have cycles that are consistently longer than the average 28-day cycle.

What if I have irregular periods or long cycles? The chances of actually having your baby on that exact date are very slim. Remember that the due date is only an estimate of when you will deliver your baby. When you line up that date with the indicator, the wheel displays your due date. The first step is locating the date of your LMP on the wheel. It’s very easy to estimate your due date if you have access to a pregnancy wheel. This is the method that most doctors use. The other way to calculate your due date is to use a pregnancy wheel. In this example, the due date would be August 8, 2018.

Change the year, if necessary (to the year 2018, in this case).

Subtract three months (August 8, 2017).

Naegele’s rule involves a simple calculation: Add seven days to the first day of your LMP and then subtract three months.įor example, if your LMP was November 1, 2017: We have created a slew of pregnancy calculators and tools to help you through your pregnancy.If you have regular 28-day menstrual cycles, there are two ways to calculate your due date. Pregnancy Calendarįollow your baby's development week by week in our article series. If you want to, you can view a sample due date report.

Timeline of Significant Milestones in Embryo/Fetal Development.

Due Dates for Multiples (Twins, Triplets, Quads).Each due date report contains the following data: A normal pregnancy can last anywhere between 38 and 42 weeks. Most are born within a week either side of the estimated due date.

On average only 5% of births take place exactly on the estimated due date. Be sure to talk to your health care provider about your due date. Every pregnancy is unique and your baby will come when it's ready. Please remember that your due date is only an estimate. If you deliver on your due date, your baby is actually only 38 weeks old, not 40. Note that your menstrual period and ovulation are counted as the first two weeks of pregnancy. Your due date is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (assuming a 28 day cycle). Pregnancy induced hypertension How is my due date calculated?

Due date predictor