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Re: Obstetric growth scans - HELPFrom: Terry J. DuBose (duboseterryj@uams.edu)Tue Dec 3 13:01:35 2002
ultrasound@obgyn.net writes: Can anyone please help me with criteria for requesting Obstetric growth scans!!!!! ----------------------------- Dear Catherina.Laubscher@chelwest.nhs.uk, I am responding to you on the assumption that you are a medical professional. This Forum is for medical professionals to discuss the use of sonography in women's health. As such, as a matter of professional courtesy, we like to identify ourselves. Public questions and discussion are more appropriate on Women's Heath or Pregnancy & Birth forums of OBGYN.net . ----------------------------- ----------------------------- By "Obstetric growth scans", I am assuming you mean study of fetal growth with serial sonographic measurements. Some have referred to this as "serial growth studies", "differential growth analysis", and we first referred to it as fetal "age range analysis" (ARA) (http://www.io.com/~dubose/bbii.html). DuBose TJ, Poole E, Butschek C, et al: Range of Multiple Fetal Parameters. Official Proceedings 1988 World Federation for Ultrasound in Medicine and Biology; J Ultrasound Med, 1988; 7:S205-206. It is an interesting problem that I fear many do not understand. It requires at lease two sonographic studies. The first is the "dating study"; the later studies are the "growth studies" for comparative growth. If you have a good dating study at 10 weeks, then if you do a growth study 20 weeks later, the fetus would be expected to grow in size that will be equivalent to 10 weeks larger during the interval time. The basic idea is that the sizes of fetal parameters grow at a relatively normal rate, and we have a huge number of researchers who have documented these throughout gestation. This growth rate can be interpreted as a relative age; that is, age is used as a surrogate for size. However, in a fat fetus with short legs, " It would be absurd to assume the AC was conceived 4 weeks before the femur, yet that is how many discuss parameter ages. It is more logical to assume the true fetal age is the multiple fetal parameters' average age (MFP AA, after Hadlock) with the femur and AC under the extreme tails of the distribution. We found that the parameter age range distribution for all parameters will be approximately +/- 5.0 percent of the fetal age or +/- 10 % for 2 SD." DuBose, Fetal Sonography, W.B., Saunders Co. 1996, p. 143. About 4 years ago there was a message (on a Midwives' list, not OBGYN.net) from a midwife who was raling about how poorly sonography estimates age and delivery dates. As I tried to defend sonography, it came to light that she had been dealing with an IUGR fetus, and had 3 sonographic studies done… by different laboratories. Each time the report came back "normal fetus", but the estimated delivery date was a couple of weeks later. Because the midwife did not understand sonographic growth studies, they kept moving the delivery date back on the assumption that the last study done would better estimate the delivery date because "it was closer to delivery". Wrong! The baby died during labor and only then was it found to be IUGR. The first study always gives the best dates, the later studies are used to compare the growth to the time interval between studies. NEVER CHANGE THE EDD of the dating study. Is that clear? I hope so, if not ask more questions. You can find a bit more related material at: http://www.obgyn.net/displayarticle.asp?page=/english/pubs/features/dissertations/dejong-summary Good luck, Terry Peace, Terry J. DuBose, M.S., RDMS Assistant Professor & Director, Diagnostic Medical Sonography Program University of Arkansas for Medical Sciences, CHRP 4301 West Markham St. Mail Slot #563 Little Rock, Arkansas, 72205 USA 501-686-6510 DuBoseTerryJ@UAMS.edu http://www.io.com/~dubose/ http://www.uams.edu/CHRP/dmshome.htm http://www.obgyn.net/us/panel/panel.htm
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