794 Correspondence

vaginal candidiasis with oral ketoconazole. Eur J Obstet Gynecol Reprod Bioi 1983;14:399-407.

3. Pietrogrande MD, Tortorano AM, Viriani MA, et al. Keto­conazole treatment of candidiasis in children's clinico­pharmacokinetic study. Pediatr Med Clin 1983;5(3): 91-94.

4. Anonymous. Ketoconazole: drug information. American Hospital Formulary Service 1984;8(2):49.

5. Anonymous. Ketoconazole investigators' brochure. Jans­sen Pharmaceutica, April, 1980.

6. Pont A, Williams PL, Azhar S, et al. Ketoconazole blocks testosterone synthesis. Arch Intern Med 1982;142:2137-2149.

7. Pont A, Williams PL, Loose DS, et al. Ketoconazole blocks adrenal steroid synthesis. Ann Intern Med 1982;97:370-372.

8. Pont A, Trachtenberg J. Hormonal changes in patients on chronic high dose ketoconazole therapy [Abstract]. Clin Res 1984;32:271A.

Fetal femur length and its relationship to birth weight

To the Editors: In a recent report by Seeds et a!. (AM J 0BSTET

GYNECOL 1984;149:233) it was suggested that a deriva­tive of the fetal femur length might be used in place of the biparietal diameter for a sonographic estimate of fetal weight. While the proposal is fascinating, further investigation is required. The concept assumes a con­stant relationship between biparietal diameter and femur length. Though each parameter individually correlates well with weight, the correlation between the twomay not be as high, especially where the possibility of growth retardation exists. Table I shows values ob­tained from three fetuses scanned within 48 hours of delivery. Their biparietal diameters and abdominal cir­cumferences are identical, yet their birth weights dif­fered by as much as 900 gm. Much of the difference results from a difference in femur length. The pro­posal by Seeds and associates ignores this possibility. Perhaps it is premature for the authors to conclude the femur-equivalent biparietal diameter is an accurate enough basis for the clinical decision of viability.

Carl P. Weiner, M.D. Division of Maternal Fetal Medicine Department of Obstetrics and Gynecology The University of Iowa Hospitals and Clinics Iowa City, Iowa 52242

Table I. Influence of head circumference and femur length upon birth weight in fetuses with similar biparietal diameters and abdominal circumferences

Biparietal Birth diameter weight (gm)

8.0 30.0 31.7 6.0 2150 8.0 30.0 29.0 6.1 1790 8.0 30.0 29.3 5.3 1290

Reply to Weiner

To the Editors:

November 15, 1984 Am J Obstet Gynecol

We appreciate the opportunity to respond to the comments of Dr. Weiner and thereby clarify the clinical utility of a femur-equivalent biparietal diameter in the estimation of fetal weight.

The limited number of references allowed with a Communication in Brief prevented us from fully doc­umenting previous work establishing a linear rela­tionship between fetal biparietal diameter and femur length. This close relationship was not an assumption, but has been shown in our laboratory1 and others.2-

4

Obviously, individual clinical exceptions do occur. In all cases it must be clearly borne in mind that an

estimation of fetal weight from ultrasonic dimensions carries a definable chance of inaccuracy. Table I clearly documents our experience and the risk of an inaccu­racy resulting from cases such as Dr. Weiner's. There­fore, the results as presented do not igiwre the possi­bility of error due to disproportionate growth but rather document the risk in our experience of inaccu­racy greater than the stated limits. Finally, we indi­cated that an estimated fetal weight based on femur­equivalent biparietal diameter might be included in the clinical estimate of viability only in the absence of an accurate gestational age and in the absence of an accu­rate biparietal diameter. It is for the reader to judge whether the observed level of accuracy justifies utiliza­tion of the method in clinical practice.

John W. Seeds, M.D. Robert C. Cefalo, M.D., Ph.D.

Watson A. Bowes, M.D. Department of Obstetrics and Gynecology Division of Maternal and Fetal Medicine 214 MacNider Building 202H University of North Carolina School of Medicine Chapel Hill, North Carolina 27514

REFERENCES

1. Seeds JW, Cefalo RC. Relationship of fetal limb lengths to both biparietal diameter and gestational age. Obstet Gyne­col 1982;60:680.

2. Jeanty P, Kirkpatrick C, Dramaix-Wilwet M, et al. Ultra­sonic evaluation of fetal limb growth. Radiology 1981; 140:165.

3. O'Brien GD, Queenan JT. Growth of the ultrasound fetal femur length during normal pregnancy. AM J OBSTET GYNECOL 1981;141:833.

4. Farrant PF, Meire HB. Ultrasound measurement of fetal limb lengths. Br J Radio! 1981;54:660.

Hemoglobin A1c levels and variant hemoglobins

To the Editors: Merrill and Trupin (Merrill P, Trupin S. Hemoglobin

A 1e levels and variant hemoglobins. AM J OBSTET Gv­NECOL 1984;149:88) have reported apparently normal levels of hemoglobin A1e despite significant elevation of blood-glucose levels in a patient with hemoglobin S. The influence of variant hemoglobin on hemoglobin A1 values measured by cation exchange column chro-