Pregnancy lasts an average of days 40 weeks from the first day of your last menstrual period LMP. Read our report on the 13 best pregnancy iPhone and Android apps of the year here.
The other way to calculate your due date is to use a pregnancy wheel. This is the method that most doctors use. The first step is locating the date of your LMP on the wheel. When you line up that date with the indicator, the wheel displays your due date. Remember that the due 8 rule for pregnancy dating calculator is only an estimate of when you will deliver your baby.
The chances of actually having your baby on that exact date are very slim. Some women have cycles that are consistently longer than the average day cycle. In these cases, a pregnancy wheel can still be used, but some simple calculations are necessary.
This is the time from ovulation to the next menstrual period. If your cycle is 35 days long, for example, then you probably ovulated on day 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.
For example, if your menstrual cycle is usually 35 days long and the first day of your LMP was November After you calculate your adjusted LMP date, simply mark it on the pregnancy wheel and then look at the date where the line crosses. That is your estimated 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.
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.
An ultrasound allows your doctor to measure the crown-rump length CRL — the length of the fetus from one end to the other. During 8 rule for pregnancy dating calculator first trimesterthis measurement provides the most accurate estimation for the age of the baby.
Your doctor may change your due date based on the ultrasound measurement. 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.
The third trimester is the least accurate time to date a pregnancy. Estimates based on an ultrasound can be off by as much as three weeks, so doctors rarely adjust dates during the third trimester. A repeat ultrasound provides valuable information about the growth of the fetus and may reassure you and your doctor that the change in due date is reasonable.
Ultrasound measurements for estimating the age of a fetus are more accurate during 8 rule for pregnancy dating calculator early stages of pregnancy. In the first few weeks, fetuses tend to develop at the same rate.
However, as pregnancy progresses, the rates of fetal growth begin to vary from pregnancy to pregnancy.
Ultrasounds are not a necessary part of prenatal care. Avoid numerous scans and have ultrasounds for medical reasons only.