Letter to the Editor: Determining Ideal Weight

In the July/August 1999 issue, I noticed your answer to a question about how to ascertain “ideal” weight for a young adolescent with anorexia nervosa who has never has a period (Q&A, page 8). While I agree with much of what you say, may I also point out the value of pelvic ultrasound as a determinant of ideal weight.

Pelvic ultrasound indicates the degree of maturity of the uterus and ovaries, and can demonstrate the presence of sufficient endometrial lining and a dominant or ovulatory follicle. Anything less than these would mean that weight is unsatisfactory. We have used this way of ascertaining satisfactory weight for many years (see Lai et al, Arch Dis Child 1995; 71: 228) and the chapter by Nicholls et al in the second edition of Lask and Bryant-Waugh’s Anorexia Nervosa and Related Disorders in Childhood and Adolescence (Psychology Press, Hove, UK, 2000).

The problem with using body mass index (BMI) or weight-height ratios is that these are arbitrary and while a BMI of, for example, 19, or a weight-height ratio of, for example, 95%, may be perfectly satisfactory for the majority, they will still be too low for some. Unless a pelvic ultrasound is conducted, too low a weight is being set and menstruation will not occur or recur.

The problem with using serum estadiol levels is that these are simply a “snapshot.” In other words, they reflect but one component of total estrogen levels at one moment in time and can be very misleading. Pelvic ultrasound is a reflection of nutritional status during the previous two months or so and is a far more reliable and valid indicator of endocrine status and maturity.

Dr. Bryan Lask, Eating Disorders Research Team • St. George’s Hospital Medical School, London

Dr. Yager replies:

Dr. Lask’s point is well taken. Pelvic ultrasound is an easy-to-use, noninvasive addition to the tools available to clinicians for estimating ideal weight.