Address correspondence to: Molly S. Chatterjee, MD, University of New Mexico, School of Medicine, Dept. of Ob-Gyn, 2211 Lomas Blvd., NE, Albuquerque, NM 87131-5286. Ph: 505-272-6381, Fax: 505-272-6385

Introduction

Accurate assessment of gestational age and evaluation of fetal growth is fundamental to perinatal care^1-6. Multiple fetal anatomical measurements have been used for ultrasound evaluation of gestation. These include fetal crown-rump lengths, biparietal diameter, head circumference, abdominal circumference, and femoral length⁶.

Streeter¹⁶, in 1920, showed that the fetal foot has a characteristic pattern of normal growth. He proposed that the fetal foot could be used to estimate gestational age. Goldstein et al found that the fetal heel ossification centers could serve as an adjunct for estimation of gestational age.Campbell et al ⁵ evaluated the fetal femur/foot length ratio and found that it was a useful parameter to help differentiate fetuses that have dysplastic limb reduction from those whose limbs are short because of constitutional factors or intrauterine growth retardation. The purpose of this study was to determine the accuracy of fetal foot length in estimating gestational age and possibly diagnose dysplastic anomalies.

Materials and methods

A prospective study was conducted in 53 normal pregnant women evaluated at the prenatal diagnosis and therapy unit of the University of New Mexico Hospital in Albuquerque, New Mexico. All the patients were certain of their last normal menstrual period, had a regular menstrual cycle, and had not experienced any vaginal bleeding since becoming pregnant. No one had taken oral contraceptives for at least three months before conception. In all patients, the gestational age was confirmed by an early abdominal or vaginal ultrasound as early as 14 weeks, either by crown rump length or by measuring biparietal diameter (BPD), head circumference, and abdominal circumference. The ultrasound measurements were made using a linear-array real-time system (ADR, Bothell, Washington) with 3.5 and/or 5 MHz transducers. We measured the fetal foot from heel to end of the big toe on plantar and lateral views (fig. 1 and 2).

Results

The gestational age ranged from 14 - 40 weeks. The relationship between fetal foot length and gestational age is shown in figure 3 and table. A significant linear relationship between those parameters (R²= 0.89, p<<0.0001) was present.

Discussion

Ultrasound has been an indispensable tool in assessing gestational age. Estimation of fetal age using multiple parameters has been described by others¹⁴.

In 1987, Munsick¹⁸ found no significant racial difference in the foot, leg, or arm measurements between nine and 20 weeks of gestation. Advances in ultrasound technology have made possible accurate measurement of fetal boots and assessment of fetal extremities. In 1987, Mercer et al⁴ described the ultrasonographic measurement of the fetal foot to estimate gestational age. They concluded that fetal foot length was a reliable parameter for estimating gestational age and was particularly useful when other parameters did not accurately predict gestational age, e.g., in cases of hydrocephalus, anencephaly or short-limb dwarfism. Two other groups^4,6 have also demonstrated that the measurement of the fetal foot by ultrasound provides a reliable estimate of gestational age.

Visualization of the foot is useful to find or exclude anomalies such as club foot⁶ and arthrogryposis. Fetal foot polydactyly has been seen in trisomy 13. Campbell et al¹⁷ found that the femur versus foot length ratio was approximately unity throughout 14 and 40 weeks of gestation. Our study demonstrates a statistically significant linear correlation between the fetal foot length and gestational age.

Acknowledgment

We are grateful to Clifford Qualles, MD, of the Clinical Research Center at the University of New Mexico, for the statistical analysis of the data.

Table 1: Nomogram of foot size against gestation

References

1.Chervenak F et al.: Antenatal Sonographic Diagnosis of Club Foot. J Ultrasound Med 4:49, 1985.

2.Mercer BM, Sklar S, Shariatmadar A, Gillieson MS and D"Alton ME: Fetal foot length as a predictor of gestational age. Am J Obstet Gynecol. 156:350-5, February, 1987.

3.Munsick RA: Similarities of Nero and Caucasian fetal extremity lengths in the interval from 9 - 20 weeks of pregnancy. Am J Obstet Gynecol 156:183-5, 1987.

4.Shalev E, Wener E, Zuckerman H, and Megory E: Reliability of sonographic measurement of the fetal foot. Journal of Ultrasound in Medicine. (JC:kbu) 8(5):259-62, May, 1989.

5.Campbell J, Henderson A, Campbell S: The fetal femur/foot length ratio: a new parameter to assess dysplastic limb reduction. Obstetrics & Gynecology. (JC:0c2) 72(2):181-4, August, 1988.

6.Streeter GL: Weight, sitting height, head size, foot length, and menstrual age for the human embryo. Contrib Embryol 11:143, 1920.

7. Chattergjee, HS , Adhate A: Ultrasonic imaging of fetal foot for evaluation of gestational age. Preceeding of the WFUMB, p. 206, July 14-19, 1986.