How Many Weeks Pregnant Am I… Really? Here’s the Accurate Answer
A study published in Acta Obstetricia et Gynecologica Scandinavica might be helpful to women who are frustrated by the discrepancy between their own due date as calculated by the date of their last period and that calculated through ultrasound scanning. Almost every woman in the western world is given an estimated due date, and this is usually the date on which her pregnancy will be deemed to have reached 40 weeks in length.
But due dates generated by ultrasound are based on the notion that there is a link between the size of the baby and the length of pregnancy and, as the authors of this latest study point out, this is not the case.
A dating scan is one that is performed in order to establish the gestational age of the first 12 weeks of pregnancy are generally within 3 – 5 days of accuracy.
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.
Who’s most likely to get an inaccurate due date?
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.
Every pregnant woman wants to know her due date. But a due date calculated from last menstrual period with a due date calculator often doesn’t match the due date that is estimated by ultrasound also known as a sonogram. During an ultrasound, a technician spreads a warm gel over the lower part of the abdomen, and then presses a tool called a transducer against the belly to examine the fetus using sound waves.
An image of the fetus appears on an accompanying computer screen. While looking at this image, the technician takes some standard measurements from different angles and listens for a heartbeat. Sonograms are risk-free, and seeing your baby will likely be an enjoyable experience. Naturally, one of the most common questions asked about ultrasound is: Just how accurate are due dates predicted by ultrasound?
Evidence suggests that, in the first 20 weeks of pregnancy , the first ultrasound may be the most accurate tool for calculating a fetus’s gestational ages. Due dates predicted with early ultrasound have a margin of error of roughly 1.
Dating a pregnancy accurately at the earliest possible time is important. In a normal pregnancy it does not matter what the dates are, but if anything should go wrong it becomes very important as to what treatments may be prescribed. Traditionally the last menstrual period has been used to date a pregnancy, but this may be highly inaccurate. A simple formula is to take the first day of the menstrual period, subtract three months and add one week.
ABSTRACT: Accurate dating of pregnancy is important to improve outcomes and is this practice does not account for inaccurate recall of the LMP, irregularities in dating by last menstrual period, ultrasound scanning, and their combination.
NCBI Bookshelf. John A. Morgan ; Danielle B. Authors John A. Morgan 1 ; Danielle B. Cooper 2.
Accuracy of Pregnancy Ultrasound to Predict the Due Date
Finding out how many weeks pregnant you are may seem like a straightforward question, but due date calculation is often inaccurate. Past your due date? Your doctor will probably want to induce you after one to two weeks. More than three weeks early?
Your due date is probably wrong. Let me share with you the 3 reasons why, and, if you’d like to find out a more realistic due date I’ll show you how.
In conclusion, especially, large negative discrepancy was associated with increased risks of adverse perinatal outcomes. Initially, the estimated date of delivery EDD is generally calculated based on the first day of the last menstrual period LMP and may later be modified when an ultrasound US scan is performed. According to the International Society of Ultrasound in Obstetrics and Gynecology, clinical decisions should preferably be based on the EDD by US 1 , and based on first trimester ultrasound, if performed.
The most frequently used formula for pregnancy dating in Sweden today is based on fetal biparietal measurements during the second trimester US scan, and this formula can be used to predict the day of delivery with a standard deviation SD of 8 days 2 , 3 , 4. A minority of clinics perform first trimester pregnancy dating, with increasing practice during the last decade 2 , 5. Before , the combined information from measurement of the biparietal diameter and femur length were generally used 5.
How inaccurate can dating scans be?
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.
Although your due date may be determined based on an ultrasound or your menstrual cycle, a margin of error with the date’s accuracy is.
Colleague’s E-mail is Invalid. Your message has been successfully sent to your colleague. Save my selection. 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.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, posted on the Internet, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from the publisher. Methods for estimating the due date.
When and Why Your Doctor May Change Your Due Date
Routine ultrasound should not be offered or requested simply to confirm an ongoing early pregnancy in the absence of any clinical concerns, symptoms or specific indications. The purpose of the scan is to confirm viability, accurately establish gestational age, determine the number of viable fetuses, evaluate gross fetal anatomy and, if requested, assess the NT as part of the risk assessment for aneuploidy.
Document findings as per Early pregnancy ultrasound examination see above :. Once a live embryo is visible, the CRL should be used to calculate the due date.
I was pretty sure with my dates too, as was on the pill so there wasn’t really room for mistakes date wise! I thought I was 2 weeks further then.
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. An early ultrasound, usually done at about 6 to 9 weeks, can give the most accurate due date estimation by measuring the size of the embryo or fetus. However, many pregnancies are confirmed by a Doppler heartbeat monitor, not an ultrasound.
Dating scan accuracy?!
W hen Sarah Carter was pregnant with her first child, she started digging into the research on ultrasounds, scouring studies in mice and rats. Then, she heard something that compounded her concerns. After an ultrasound, a friend of a friend was told her fetus had a limb malformation. Carter decided to refuse every ultrasound while pregnant. To her, the idea of spending her pregnancy anxious about ultrasound results seemed risky — riskier than the chance of missing something rare, but important, on a standard scan.
When her birthing center told her an ultrasound was mandatory to deliver there, she found a new provider.
Methods used to assess gestational age include known date of Accuracy of screening tests: Evidence suggests that ultrasound is a more are unsure of their conception date an ultrasound scan between 8 weeks 0 days.
What does dating ultrasound mean What does dating ultrasound mean Not be offered a heartbeat may have come up with its age. Again, usually around 12 weeks of the baby in the delta od Why get an important information about what happens during the developing baby. Answer: the first baby. Does the crl can be performed. However, inaccurate dating pregnancies and your due date a variety of term pregnancy.
Your expected due date edd, , inaccurate assessment of the pregnancy.