Expert: Catherine Beier MS CBE - 2/3/2010

Question
Hi Catherine,
    Thanks for your amazing and informative answer. You have really helped to clarify matters. You mentioned that the most accurate time to have an ultrasound done for dating purposes is between 8-10 weeks. If ultrasounds and taken before this time, say at 6 weeks, then how accurate are they? I had an ultrasound taken at 6 weeks, 1 day, and the crl was about 4.5-5 mm. Does this sound accurate to you? Then at around 9 weeks, the crl was about an inch, and at 11 weeks the crl was around 2 inches. Do these measurements sound like the average measurements of what the crl should be at these times? I gave birth to my wonderful child on 6/26/08, even though my due date was on the 11th or 14th of July if a 32 day cycle is taken into consideration. My lmp was on 10/5/07. I am still confused if since I gave birth a little early, can this mean I conceived in September or even earlier. I received a good answer on this site by another wonderful expert, who said that there is no way I could have conceived in September or earlier, that some babies just come a bit earlier, and that a full term baby is anywhere from 37 to 42 weeks. Do you agree with this answer? Is there even a remote possibility that I conceived in September or even earlier? I worry because my baby was born a bit small,(a little more than 6 pounds), and during labor there were times where the heartrate would drop. Thankfully I gave birth naturally with the help of an amazing doctor, but the umbilical cord was wrapped around my baby's neck. Thankfully my baby is happy and healthy, but since the baby was born a bit small does this indicate iugr, and if I conceived earlier and the ultrasound was off, then I worry that the baby was inside my womb longer than I thought, which is why maybe there was a heart rate drop during labor and why my water broke early? As you can see, I am still confused. Awaiting your answer.

Answer
Hilary,


Ultrasounds around 6 weeks or before vary widely in accuracy because it's difficult to measure the gestational sac accurately (which isn't a very reliable measure under the best circumstances) and a day can make a huge difference in what type of development is seen. One day the sac can still be empty and the next, the fetal pole might be seen. The technician's skill and the quality of the equipment also dictate how reliable the measures are.


But, since you did have another u/s at 9 weeks, then it's really a moot point how accurate the first was - you have a better measure to rely on.


According to the CRL table of information I provided in my last answer, you can see for yourself that the measurements at the 9 week and 11 week ultrasounds correspond well to CRLs at those times. (You have to convert from inches to cm first). They are right in line with what you'd expect.


Again, here is the chart of the typical CRLs (in cm, not mm) at each early week:

6.1 Weeks: 0.4 cm
7.2 Weeks: 1.0 cm
8.0 Weeks: 1.6 cm
9.2 Weeks: 2.5 cm
9.9 Weeks: 3.0 cm
10.9 Weeks: 4.0 cm
12.1 Weeks: 5.5 cm
13.2 Weeks: 7.0 cm
14.0 Weeks: 8.0 cm


Now, having read through the rest of your many questions, I fear you're manufacturing a lot of fears about what sounds like a typical, uncomplicated birth.  Nothing you've indicated is out of the ordinary or suggests true complications of any kind.


I'll address each point separately:


You're putting way too much faith in due dates - babies come when babies are ready.  Less than 1% of babies are born on their due dates.  I do agree with the other answer you received - anywhere from 37-42 weeks is considered term; your baby arrived right in line with normal ranges.


So, the fact that your baby arrived a little early does not change when you conceived - it just means your child was ready to be born sooner than later.  Personally, I've never made it to 38 weeks - my kids are just ready to be born early.  No, I do not see it possible that you conceived earlier or in September (remember, you had a period in Oct - that should make it obvious you didn't conceive in September) - the baby was just ready sooner than later.


It would seem you are also overtly worrying about birth weight.  6lbs is not considered small in the least - it's completely within the average range, especially if you deliver before 40 weeks.  I'm not certain why you're considering this to be small.


In terms of IUGR: absolutely not.  If your baby was 3 lbs at term, yes - but 6lbs = normal birth weight.


It's also completely normal and expected for the heart rate to drop and rise during labor.  We worry if a heart rate is nonreactive, meaning it either stays a flat rate during contractions or doesn't show good rebound after them.  The expected pattern is for the heart rate to dip during a contraction, then rise once the contraction ends. As long as it dips and returns to an average rate, that is what we want to see.  So, again, I think you're concerns here are unfounded as well.


Heart rates can also drop due to your position during labor - if you're lying on your back you can restrict oxygen and blood flow to the baby - or the baby's position.  Also, the use of labor induction methods, such as pitocin, can also cause heart decels.  But again, as long as the heart tones return to average ranges, then there's no overt cause for concern.


And to finally address your last fear - the cord around the neck.  This *is not* by itself, a complication or concern at birth.  25% of all babies are born with the cord wrapped around some part of their body, including the neck, and sometimes it's even wrapped multiple times.


Many people falsely think the baby can't get oxygen if the cord is around the neck in the womb - but they fail to realize the baby is not breathing through its lungs yet - it receives oxygen through the cord.


So, concerns only arise if the cord is *compressed around the neck* or some other part of the baby's body, meaning that blood flow (and thereby oxygen), aren't reaching the baby in full supply.  This can result in lowered heart rates or nonreactive heart tone patterns  - but when true cord compression is occurring, then the heart rate is not likely to return to normal - it stays low.  Maternal positional changes during labor can help alleviate the pressure on the cord and help the heart rate return to normal, but when it is truly compressed, this does not help.


True cord compression is actually quite rare.  The umbilical cord is coated in a substance called Wharton's jelly, which helps to make it resistant to compression.



In summary, I think you worry too much;-)  


Your water broke early because your baby was ready to be born, not because of some complex medical condition or other complications.  Heart rate drops are normal and expected - if the heart rate drop was truly a concern, you'd have been rushed off to the OR for an emergency c-section - that didn't happen, which indicates the decels were within the normal range.  If the cord were truly being compressed, you'd again have been rushed off for a c-section - which didn't happen.


And finally, if IUGR or a post-term baby had even been suspected or considered, then the pediatrician who performed the newborn assessment would have said something about it.  Your fear that the baby was in the womb longer than you thought is also unfounded - there are physical signs when this occurs, such as a lack of vernix on the baby, very long fingernails, dried looking skin and the placenta can also show signs of calcification or other deterioration to indicate that it was aging.  


So, Hilary, my best advice is to relax and enjoy your child - they grow up too fast as it is~


Best,
Catherine