Volume 179, Number 5 Am] Obstet Gynecol

occur in dichorionic pregnancies, yet the authors' pre­senting symptom of "rapidly increasing fundal height," as well as a single placenta on ultrasonography, same-sex fe­tuses, and significant differences in both fetal weight and amniotic fluid volume, can all occur in dichorionic preg­nancies.

Only a first-trimester sonogram or careful postpartum examination of placental membranes can differentiate between monochorionic and dichorionic placentation. Even deoxyribonucleic acid studies would not be helpful because monozygotic (identical) twins can be either monochorionic or dichorionic.

In the Discussion that follows the article, Christmas asks " ... why a 'syndrome' would behave so differently from patient to patient." How can we be sure that all of the authors' cases were truly at risk for the syndrome?

Douglas W Hershey, MD Prenatal Diagnosis of Northern California Medical Group, Inc, 1315 Alhambra Blvd, Suite 210, Sacramento, CA 95816

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Estimating date of confinement in in vitro fertiliza­tion pregnancies To the Editors: Chervenak et al (Chervenak FA, Skupski DW, Romero R, Myers MK, Smith-Levitin M, Rosenwaks Z, Thaler HT. How accurate is fetal biometry in the as­sessment offetal age? Am] Obstet GynecoI1998;178:678-87) have demonstrated persuasively just how accurate fetal biometry can reflect fetal age. There has been much debate in the past about whether ultrasonic biometry should completely override certain menstrual dates, 1, 2

because most ultrasonographic charts themselves were generated from certain menstrual dates.3 Charts gener­ated from data provided by studies of in vitro fertilization pregnancies cannot be subject to this particular criticism when used to date natural conceptions. However, how would the authors handle the dating of in vitro fertiliza­tion pregnancies in the future? It is unlikely that ultra­sonographic biometry will fall precisely on the mean for the calculated fetal age. Would the authors entirely ig­nore (at least for the purposes of dating) any differences between the measured and expected biometry? Or would they only accept the calculated fetal age if the biometric value falls within the 95% confidence intervals? Their data show that a small number of fetuses will fall outside the 95% confidence intervals. Should these fetuses' ages be reassigned? In other words, can these charts now be used to date in vitro fertilization pregnancies in the same way that menstrual charts have been used to date natural conceptions?

David JR Hutchon, MB Department of Obstetrics and Gynaecology, Memorial Hospital, Darlington, United Kingdom DL3 6HX

Letters 1381

REFERENCES

1. Mongelli M, Wilcox M, Gardosi J. Estimating the date of con­finement: ultrasonographic biometry versus certain menstrual date. Am] Obstet Gynecol 1996;174:278-81.

2. Hutchon DJ. Estimating the date of confinement [letter]. Am] Obstet GynecoI1996;175:510-1.

3. Hall MH. Definitions used in relation to gestational age. Paediatr Perinatal EpidemioI1990;4:123-8.

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Reply To the Editors: We thank Hutchon for his thoughtful let­ter and question. In our view, if there is a difference in gestational age based on in vitro fertilization data and ul­trasonographic data, this difference should be resolved in favor of the in vitro fertilization data, which determine the "true" gestational age. This is not the case for men­strual age, which is subject to several sources of varia­tions.

Frank A. Chervenak, MD, Daniel W Skupski, MD, Rnberto Rnmero, MD, Michelle Smith-Levitin, MD, Zev Rnsenwaks,

MD, and Howard T. Thaler, PhD Department of Obstetrics and Gynecology, New York Hospital-Cornell Medical Center; 525 E 68th St, New York, NY 10021

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Hyperemesis gravidarum is not associated with hypofunction of the pituitary-adrenal axis To the Editors: We read with interest the recent paper by Safari et al (Safari HR, Alsulyman OM, Gherman RB, Goodwin TM. Experience with oral methylprednisolone in the treatment of refractory hyperemesis gravidarum. Am] Obstet Gynecol 1998;178:1054-8) on methylpred­nisolone in the treatment of hyperemesis gravidarum.

There have been several recent reports of successful use of corticosteroids in this disorder. The rationale for this treatment is based on the observation of relative adrenocortical insufficiency as a secondary effect of adrenocorticotropic hormone deficiency. 1 Alternatively, corticosteroids may act on a vomiting center in the brain (chemoreceptor trigger zone). However, it was shown >20 years ago that hyperemesis is not associated with pi­tui tary-adrenal deficit. 2

To clarify whether adrenocortical impairment exists in hyperemesis gravidarum, we began a study to explore the pituitary-adrenal axis in pregnant women who had this disorder and in pregnant women who did not. We now take this opportunity to report the results of our study so far.

The subjects recruited to date are 5 women with hy­peremesis (age 26 ± 3 years, last menstrual period, 11 ± 2.5 weeks) and 7 normal pregnant women (age 27 ± 4 years, last menstrual period 10.5 ± 2.7 weeks). Blood sam­ples for assay of adrenocorticotropic hormone and corti­sol were obtained every hour for 24 hours. The data were analyzed by Student t test for unpaired data.

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The mean 24-hour plasma concentration of adreno­corticotropic hormone was significantly higher in women with hyperemesis than in women without (19.8 ± 3.2 pg/mL and 14 ± 2.2 pg/mL, respectively; P< .05), as were mean 24-hour cortisol concentrations (220 ± 30 ng/mL vs 150 ± 25 ng/mL, P< .05).

Analyzing the data divided into 4-hour periods, we found that plasma cortisol concentrations were signifi­cantly different between groups at 8 PM to midnight, mid­night to 4 AM, and 4 to 8 AM.

These results show no impairment of adrenocortical function in hyperemesis but rather hyperfunction of the hypothalamic-pituitary-adrenal axis. This means that cor­ticosteroid replacement therapy has no basis in this disor­der.

The mechanism by which corticosteroids suppress the

November 1998 Am] Obstet Gynecol

severe vomiting is probably a direct effect on a vomiting center in the brain.

Antonio la Marca, MD, Giuseppe Morgante, MD, and Vincenzo De Leo, MD

Department of Obstetrics and Gynecology, University of Siena, Policlinico Le Scotte, 53100 Siena (SI), Italy

REFERENCES 1. Wells eN. Treatment of hyperemesis with cortisone. AmJ Obstet

Gynecol 1953;66:598-601. 2. Kauppila A, Ylikorkala 0, Jarvinen PA, Haapalahti J. The func­

tion of the anterior pituitary-adrenal cortex axis in hyperemesis gravidarum. Br J Obstet Gynaecol 1976;83: 11-4.

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