An early ultrasound, which can more accurately date the pregnancy. Just be aware, however, that not all women get an early ultrasound. Pregnancy milestones such as the first time the baby's heartbeat is heard around week 9 or 10, though it can vary and when you first feel fetal movement on average between 18 and 22 weeks, but it can be earlier or later , can give clues as to whether your due date is accurate.
Your fundal height, which is the measurement from your pubic bone to the top of your uterus, is checked by your practitioner at each prenatal visit and helps confirm your due date. Whether you're trying to avoid being very pregnant in the middle of summer or are a teacher who wants to maximize time off with your little one, you can try to time when you conceive in order to "plan" your due date.
But even if you're one of the lucky ones who's able to get pregnant when she really wants to, just remember that you probably won't be able to map out exactly when you'll give birth to the day or even the week or month! Still, you can try our Ovulation Calculator , which uses the date of your last menstrual period and your typical cycle length to discover the days you're most likely to be fertile and increase your chances of conceiving.
Yes, your due date can change. It may be that you have irregular periods and your early ultrasound dating was off, or that your first ultrasound was in the second trimester. It could also be because your fundal height is abnormal, or your levels of alpha-fetoprotein AFP , a protein made by the baby, are outside the usual range.
Talk to your practitioner if you have any questions or concerns. At the point of 42 weeks, births are commonly considered 'post-term'. If you reach this point, your hospital will likely induce labour for the safety of the baby. You can learn more about this and about due dates in this article by the Essential Parent website. The due date charts show possible due dates based upon data from a birth survey carried out by Spacefem.
It's important to remember that your birth date probability will vary based upon many factors, including your age, health, ethnic origin and whether you've given birth before.
If you have any problems using this pregnancy calculator, please contact me. Warning: It is necessary to enable JavaScript for full calculator functionality. Here are some instructions for how to enable JavaScript in your browser. Popup calculator Copy a link to this page Print this page Email a link to this page Scroll up to form What does this mean? Quick Search:. First day of last period:. The Pregnancy Calculator can estimate a pregnancy schedule based on the provided due date, last period date, ultrasound date, conception date, or IVF transfer date.
Related Ovulation Calculator Conception Calculator. Childbirth usually occurs approximately 38 weeks after conception, or about 40 weeks after the last menstrual period. The World Health Organization defines a normal pregnancy term to last between 37 and 42 weeks. During a person's first OB-GYN visit, the doctor will usually provide an estimated date based on a sonogram at which the child will be born, or due date. Alternatively, the due date can also be estimated based on a person's last menstrual period.
While the due date can be estimated, the actual length of pregnancy depends on various factors, including age, length of previous pregnancies, and weight of the mother at birth. This initial estimation may then be superseded or confirmed by an ultrasound. Read more about ultrasound on this page or our due date page. Pregnancy is counted from a women's last menstrual period because the start of a period is easily observable and usually known to a woman whereas the date of conception is much less likely to be known.
Historically, the first day of the last menstrual period LMP became the date from which pregnancy is counted even though conception occurs about two weeks later. The LMP formula is good for working out an initial age of pregnancy but ultrasound is more accurate. Ultrasound in the first trimester is the most accurate method of dating pregnancy. If there is a significant difference between gestational age according to LMP and gestational age according to the ultrasound, you may be given a new gestational age and due date based on the ultrasound measurements.
Your pregnancy may also be dated by ultrasound measurement if an LMP formula was not appropriate for your pregnancy for any reason. LMP formulas are not suitable in several situations including the following: LMP is not known or is not certain, birth control pills were taken in the two months before LMP, the menstrual cycle is irregular, you are carrying multiples twins or more.
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