The estimation of conception date is based on this, but is rarely ever exact since it is difficult to know exactly when ovulation occurs. Estimating conception date can also be more difficult for women who have irregular periods, or for those who don't remember the first day of their last period. In cases like these, one of the more accurate ways to estimate gestational age is through the use of an ultrasound.
An estimated due date, usually based on a sonogram, is typically obtained from a healthcare provider during a prenatal visit. Based on this due date, a range of possible conception dates can be calculated. An ultrasound, on a basic level, uses sound waves to create images of internal body structures. An ultrasound used in the context of examining the progress of the fetus in pregnant women is referred to as an "obstetric ultrasound.
Ultrasounds can be used to measure a fetus as early as five or six weeks following the mother's last menstrual period. If you had a Day 3 embryo transfer, count days. Your healthcare provider might revise your due date if your baby is measured during a first trimester ultrasound scan and found to be much bigger or smaller than expected for gestational age.
This is more likely to happen if you have an irregular menstrual cycle length that makes it hard to pinpoint the date of conception. Your healthcare provider will measure your baby during that ultrasound exam to figure out how far along your baby is and then provide you with a new due date. If you already know your due date, you can use this calculator to see your pregnancy calendar. It will tell you when you'll hit various milestones, like when your baby's heart starts beating, and when you may be due for prenatal tests and prenatal care.
You'll also find what your baby's sign and birthstone will probably be and which famous people were born on your due date. Of course, a due date calculation is always approximate, whether it's from our tool or from your doctor or midwife. Only 1 in 20 women delivers on her due date. You're just as likely to go into labor any day during the two weeks before or after.
Want more information about how the weeks, months, and trimesters of pregnancy are counted? See our pregnancy timing chart. BabyCenter's editorial team is committed to providing the most helpful and trustworthy pregnancy and parenting information in the world.
When creating and updating content, we rely on credible sources: respected health organizations, professional groups of doctors and other experts, and published studies in peer-reviewed journals. We believe you should always know the source of the information you're seeing.
Learn more about our editorial and medical review policies. Join now to personalize. Choose a calculation method Last period Conception date I know my due date. First day of my last period. See your timeline. Sources BabyCenter's editorial team is committed to providing the most helpful and trustworthy pregnancy and parenting information in the world. PMID 2. PMID 3. PMID 4. Clinical management guidelines for obstetricians-gynecologists. Number 55, September replaces practice pattern number 6, October Management of Postterm Pregnancy.
Obstet Gynecol. PMID 5. JAMA ; PMID 6. Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol. PMID 7. Birth weight from pregnancies dated by ultrasonography in a multicultural British population.
Sep 4 ; PMID 8. Ultrasonography in Pregnancy. American College of Obstetricians and Gynecologists. Conceptional age, menstrual age, and ultrasound age: a second-trimester comparison of pregnancies of known conception date with pregnancies dated from the last menstrual period. PMID: Trauma in pregnancy. Emerg Med Clin North Am. Hay DL, Lopata A. Chorionic gonadotropin secretion by human embryos in vitro.
J Clin Endocrinol Metab. Wilcox AJ, et al. Time of implantation of the conceptus and loss of pregnancy. N Engl J Med. Lohstroh P, et al. Daily immunoactive and bioactive human chorionic gonadotropin profiles in periimplantation urine samples. Biol Reprod.
Cervical insufficiency. The American College of Obstetricians and Gynecologists. Berghella V, et al. Ultrasound Obstet Gynecol ;
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