Baby Measuring Small

[People_Person]

I went for my initial ultrasound several weeks ago - based on my LMP and the u/s measurement the baby measured right on target for 7 weeks.  When I went for my first trimester screen last week the ultra sound neck measurment seemed good (1.3) but the baby measured small (11.0 weeks versus 12.3 weeks - baby 4.5 centimeters).  Ironically, I had volunteered to come in for an utrasound the following day for a training session at my doctor's satellite office and once again, the baby measured small (11.3 versus 12.4).  So, there's no question in terms of there being some sort of error in the u/s reading - it was accurate.  I've read that generally babies should measure right about on track at least through the first 4 months or so in terms of being a certain size for their gestational age.  Therefore, when we look at my baby being about 7-10 days behind, it seems fairly significant even though it's only a few millimeters.  What's most scary is that I understand this may be an indicator of a chromosome abnormality.  Since I'm just over 13 weeks now, I'm told I am too late for the CVS test.  But, I'm too early (by 3-4 weeks or so) for the amnio.  So, I have to wait for a month to find out if there is a problem.  Can a baby measure small at 12 weeks after measuring right on target at 7 weeks and still go on to be healthy?  Is a chromosome problem likely??  Please note that I do not have the full results from the 1st trimester screen (blood work due back later this week).  Also, I am 38 and am due in August.  This is a first pregnancy.  All other health is good except for having been on medication for blood pressure which I have been taking for over 10 years (Procardia XL)...BP is controlled at approx 118/75.  Any info is appreciated!

[People_Person]

Thank you for your response!  Just one point of clarification...I'm pretty sure the ultrasound(s) was (were) accurate given the fact that I had 2 (one on Monday and one on Tuesday).  They were done at different offices on different machines with different techs.  The first one measured the baby at 11.0 weeks and the one the day later was 11.3 weeks.  Anyway, I just wanted to point that out just in case it made a difference in your assessment.  I am impatiently waiting for the First Trimester Screen results which I am will receive later this week.  For now, I'm planning on the amnio but if the full screen comes back good (u/s and bloodwork) and a follow up u/s is good I may decide against it.  I'm not even sure I would be this worried except for the fact that my doctor sounded so alarmed...nearly morbid.  Perhaps he's just being extra careful which I can understand.  But for a worried Mom to be...it's very scary!

[Elaine Brown, MD]

Hi!
I would be more concerned if you hadn't mentioned that the neck measurement is so good.  The nuchal translucency is fairly sensitive, and the fact that it is normal is very reassuring.  Your measurements are close to being within the margin of error for the ultrasound--which should be 5-7 days in the first trimester. so I am going to guess that is what the problem is--the ultrasound, not the baby.

If you are concerned, though, carefully consider your own personal risk benefit ratio for a genetic amniocentesis.  I would recommend having the procedure done by a perinatologist (as opposed to a general OB/gyn)--they can sometimes do them a little sooner than 16-17 weeks, and their complication rate is lower.  The procedure is not nearly as awful as it sounds.  (I've been through three),  Also, you can get the FISH studies with a turn around time of 2-3 days.

In the mean time, a follow up ultrasound for another point on the graph would be useful--

I'll bet your baby is just fine!  Congratulations!
Dr B