When LMP and Ultrasound Dates Don’t Match: When to Redate?

Throughout my pregnancy , I’ve received two different due dates — one came from my very first ultrasound, when my baby was barely the size of a blueberry, the date that was then subsequently stamped on my record as “the” due date. But then there was a second date, the one that showed up on my next couple of ultrasound scans. This date was a few days earlier. It’s also the date that I prefer, not only because I’m now 38 weeks pregnant and ready to get this baby out, but because it matched the date I’d calculated on my own using information I looked up. And how much does it really matter? After all, as many moms know, due dates are just educated guesses. Traditionally, estimated due dates are calculated by taking the start date of a woman’s last menstrual period and adding a year, subtracting three months and adding seven days, a method known as Naegele’s rule. But that method doesn’t account for irregularities in a woman’s menstrual cycle — if she has a longer or shorter cycle than 28 days or any variability with ovulation, for example. That’s why the American College of Obstetricians and Gynecologists recommends doctors use ultrasound measurement in the first trimester to establish an estimated due date.

Accuracy of Ultrasound in Dating your Pregnancy

The role of ultrasonography in obstetric practice has continuously evolved since its introduction more than 40 years ago. Indeed, it is difficult to imagine a modern obstetric practice without access to the information provided by real-time ultrasound. Using this imaging technique, clinicians can detect pregnancy as early as 3 weeks after conception, confirm or revise gestational age with reasonable accuracy, diagnose multiple gestation in early pregnancy, confidently diagnose fetal death at any gestational age, assess fetal well-being, evaluate amniotic fluid volume, and diagnose a broad variety of fetal malformations.

Advances in sonographic imaging in the past decade are attributable to both improved image resolution and to better clinical interpretation of ultrasound findings. It is reassuring that in human pregnancy no adverse bioeffects appear to be caused by diagnostic ultrasound.

How reliable is ultrasound accuracy for pregnancy? Let’s find out. How Accurate Are They for Predicting Due Date? This is a top-of-mind.

If you were having regular periods before pregnancy, your doctor will calculate your due date based off of your last menstrual period. This goes back to the fact that in order to get pregnant, your body ovulated—or released an egg—roughly in the middle of your cycle and it was fertilized by sperm. That was the moment of conception. Is an ultrasound a more accurate way of finding out my due date?

If you are having irregular cycles before getting pregnant, an ultrasound is usually done to find out how far along you are. An ultrasound is actually the most accurate way to date a pregnancy because all fetuses grow at a consistent rate during the first trimester and early second. Your doctor will go with the due date obtained from your ultrasound. What happens if my baby is measuring big or small later on?

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MFM mums share their stories plus expert sonographers explain why it happens and what to do if you’re told your due dates are wrong. By Rachel Mostyn. Original date given was 18 December but at the scan it was moved to 31 Dec. Unless you have an early pregnancy scan most of you will be given your estimated due date at the week scan. Of course you have probably already used an online due date calculator.

Gestational age is also estimated by using ultrasound measurements of the fetus by up to 2 weeks, even with an accurate LMP date confirmed by other tests.

The first trimester is defined as the first 13 weeks of pregnancy following the last normal menstrual period some authors refer to early pregnancy as weeks. It can be divided into a number of phases, each of which has typical clinical issues. These phases are:. For a more detailed look at the stages of the first trimester see: ultrasound findings in early pregnancy. The earlier in pregnancy a scan is performed, the more accurate the age assignment from crown rump length.

The initial age assignment should not be revised on subsequent scans 5. Please Note: You can also scroll through stacks with your mouse wheel or the keyboard arrow keys. Updating… Please wait. Unable to process the form. Check for errors and try again.

Viability Ultrasound

Pregnancy math can be a little murky. After all, unless you went the IVF route, your physician has no way of knowing the exact time of conception. Because of this, pregnancy is calculated from the first day of your last menstrual period or LMP. From that day, weeks of pregnancy is officially counted, and your doc or midwife busts out the red pen and marks your due date on the calendar.

Sometimes, however, the due date may be revised. It can be pretty difficult to determine a due date using the date-of-last-period method for women with irregular cycles — which is why an ultrasound exam is often required to determine gestational age.

“Definitely agree that dates from early scans are not accurate. Just half a millimetre at such an early stage can change your date by a week. Your.

Obstetric ultrasound, also known as prenatal or pregnancy ultrasound, uses high-frequency sound waves to produce images of a developing embryo or fetus. Your doctor will use information from obstetric ultrasounds to track pregnancy progress, gestational age and help predict delivery dates. During an obstetric ultrasound, you will be on a bed, usually on your back. You may be asked to change position during your scan. Changing position helps move your organs and the fetus into a better position so the sonographer can capture high-quality images.

If you have an Alberta Health Care card or valid health care card from out of province, there is no cost for an obstetric ultrasound except in Quebec. An obstetric ultrasound scan lasts approximately 45 to 60 minutes. If you have multiple fetuses, the exam will take longer, usually about 90 minutes. One significant other is welcome to join you in the room for the entire duration of the exam.

How accurate is my ‘due date’?

It is common to be given a single ‘estimated due date’ EDD which corresponds the point at which it is estimated that your pregnancy will have lasted 40 weeks. It may be more helpful to be prepared for you baby arrive some time after 37 weeks, and to focus on 42 weeks as the time by which you have a good chance of having given birth. Many women with longer pregnancies find that everyone is asking whether they have had their baby yet, and that health care workers start to suggest inducing labour.

Research seems to dating that early ultrasounds are accurate to within three or four days. By a 20 week ultrasound, they are ultrasound accurate to within a.

Read terms. Pettker, MD; James D. Goldberg, MD; and Yasser Y. This document reflects emerging clinical and scientific advances as of the date issued and is subject to change. The information should not be construed as dictating an exclusive course of treatment or procedure to be followed. As soon as data from the last menstrual period, the first accurate ultrasound examination, or both are obtained, the gestational age and the estimated due date EDD should be determined, discussed with the patient, and documented clearly in the medical record.

Subsequent changes to the EDD should be reserved for rare circumstances, discussed with the patient, and documented clearly in the medical record. When determined from the methods outlined in this document for estimating the due date, gestational age at delivery represents the best obstetric estimate for the purpose of clinical care and should be recorded on the birth certificate. For the purposes of research and surveillance, the best obstetric estimate, rather than estimates based on the last menstrual period alone, should be used as the measure for gestational age.

For instance, the EDD for a pregnancy that resulted from in vitro fertilization should be assigned using the age of the embryo and the date of transfer. As soon as data from the last menstrual period LMP , the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record. For the purposes of research and surveillance, the best obstetric estimate, rather than estimates based on the LMP alone, should be used as the measure for gestational age.

An accurately assigned EDD early in prenatal care is among the most important results of evaluation and history taking.

Can your pregnancy scan give the wrong due date?

NCBI Bookshelf. John A. Morgan ; Danielle B. Authors John A. Morgan 1 ; Danielle B. Cooper 2.

Is an ultrasound a more accurate way of finding out my due date? If you are having irregular cycles before getting pregnant, an ultrasound is.

A dating scan is an ultrasound scan to determine how many weeks pregnant you are and your due date. Read on for more information about what a dating scan offers. A dating scan might be recommended before 12 weeks to confirm your due date if you are unsure of your last menstrual period or your date of conception. The scan is optional and not everyone will have it. You can discuss whether you want or need a dating scan with your doctor or midwife.

If you choose to have a dating scan, it will most probably be your first scan. You will need to get a referral from your doctor or midwife for a dating scan. Most women can instead have their first scan at 11 to 13 weeks — this is usually called the week scan. A dating scan is carried out by ultrasound. A sonographer, who is usually a radiographer or a midwife trained in ultrasound, will complete your scan.

If the scan is after 10 weeks, ultrasound recordings are usually made through your abdomen. The sonographer will put gel on your abdomen and move a hand-held device called a transducer, back and forward over your skin. In some situations, such as when the scan is completed before 10 weeks of gestation or you are overweight, you may also need a vaginal scan.

Gestational Age Determination by Ultrasound