Can 6 Days Really Make A Difference?

I have a client who had an initial early ultrasound and based on that test and her last menstrual period, giving her a due date of the 26th. When she had a second ultrasound a couple of months later, the technician said that the baby was measuring a week older due to length. So, the next person she saw in her care providers' office changed her due date- decreasing it by 6 days! 


I discussed with her how important those six days may really be. In her practice they consider their patients late at 41 weeks and I knew she was shaving almost a week off of missing an induction! So, are six days really a big deal?



Your baby is considered premature if it is born before the completion of 37 weeks. Premature babies tend to need more nursery care due to "wet" lungs and do not often nurse as well as a full term baby. At that point they are usually just fine and need very little extra care. They often do not suffer the same issues as a very premature baby- more sickness in the first year, developmental delays, etc. I am amazed at the moms who seem to think as long as they have reached the end of the 36th week they are not considered premature. But it is the completion of the 37th week that is the key. So if your guesstimate of your due date is off by a week- you can see how inducing can cause some real issues for babies.


Remember due dates are estimates. But the ACOG statement says, "Most women give birth between 38 and 42 weeks of pregnancy. But very few babies are born on their due dates. It is normal to give birth as much as 3 weeks before or 2 weeks after your due date. "  So, shaving a week off on the front end means increasing your chance of an induction that is absolutely not necessary and definitely has risks associated with having one.


So how accurate is an ultrasound for determining due dates? Here is a site that explains things extensively. Gestational age is determined using  The Crown-rump length - "This measurement can be made between 7 to 13 weeks and gives very accurate estimation of the gestational age. Dating with the CRL can be within 3-4 days of the last menstrual period. "  The Biparietal diameter or The Femur length can also be used. " Dating using the BPD and FL should be done as early as is feasible." So the earlier the more accurate!  The Abdominal circumference, "reflects more of fetal size and weight rather than age. "


So the sooner the US the more accurate. http://www.ob-ultrasound.net/joewoo3.html#5a , "You should always use the result of a scan that is done earlier on in pregnancy for 'dating' purposes as it will be more accurate. In the later part of pregnancy the measurements will be affected by growth variations and will no longer reflect the fetal 'age' correctly." So don't let them change your date based on a later ultrasound! "A scan is generally booked at about 7 weeks to confirm pregnancy, exclude ectopic or molar pregnancies, confirm cardiac pulsation and measure the crown-rump length for dating. 


Remember that, "In the third trimester, fetal ultrasound does not accurately determine fetal age or weight." per http://www.webmd.com/baby/fetal-ultrasound?page=4  Also, "the effects of prolonged fetal ultrasound exposure have not been determined. So the U.S. Food and Drug Administration (FDA) does not recommend fetal ultrasound for nonmedical reasons, such as for identifying the sex of the fetus or as personal keepsakes."


Suite 101 states, "The reality is that all medical testing, including ultrasound used to determine the weight of your baby, is not 100% accurate. Not only is it recommended that you ask your provider about the accuracy of ultrasound testing to estimate weight before you make any decisions, but remember that the size of your baby may not be prohibitive in having a vaginal birth. It is important to be informed about ways to encourage labor to happen spontaneously and how to work with your body even if there is suspicion that your baby is big.

Read more at Suite101: Ultrasound and Weight of Your Baby: Reviewing the Accuracy of Ultrasound to Measure the Infant's Weight  Ultrasound should not be used to scare women into induction due to a "large" baby. Women give birth to large babies without incidence all the time! And the ultrasound measurement could be off by as much as two pounds!

I often ask a mom how she will feel if she is induced for a large baby and the induction fails. She is in the OR for a cesarean and the baby is delivered and weighs in at 7 pounds. This estimated over 9 pound baby did not loose two pounds during the labor!