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Early Human Development 41 (1995) 159-166

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Penile tumescence in the human fetus at term - - A preliminary report Hiroaki Shirozu a, Takashi Koyanagi *b, Takeshi Takashima a, Naoki Horirnoto c, Kouhei Akazawa d, Hitoo Nakano a aDepartment of Gynecology and Obstetrics, Faculty of Medicine, Kyushu University 60, Maidashi 3-1-1, Higashi-ku, Fukuoka 812-82, Japan bMaternity and Perinatal Care Unit, Kyushu University Hospital, Fukuoka, Japan CDepartment of Physiology, School of Medicine, Akita University, Akita, Japan aDepartment of Medical lnformatics, Kyushu University Hospital, Fukuoka, Japan Received 7 November 1994; revision received 12 December 1994; accepted 24 December 1994

Abstract The aim of this study is to reveal whether the penis per se actually becomes tumescent and flaccid, in time sequence, in the human fetus at term. We observed the fetal penis with realtime ultrasonography in 50 male human fetuses at 36-39 weeks' gestation and measured the penile length once at a given time per l-min epoch for each case during the 60-min window of examination. Thirty-eight were excluded due to a lack of continuous ultrasound visualization of the penis. Penile length changes were statistically analyzed for the remaining 12 fetuses using the 'least median of squares regression'. Penile length was seen to be significantly stratified into two groups: 22.5% at tumescence (group median = 20.8 mm) and 77.5% at flaccidity (group median = 16,0 mm). Penile tumescence was found to occur at the following frequency during the given observation period: once in 41.7%, twice in 50.0% and three times in 8.3% with durations ranging from 5 to 17 min, These findings indicate penile tumescence exists in the term fetus. The frequency and duration of penile tumescence are in good correlation with neonates.

Keywords: Penile tumescence; Penile length; Human fetus; Real-time ultrasonography

1. Introduction Birnholz first reported that real-time u l t r a s o u n d could visualize fetal genitalia at as early as 15 weeks' gestation onwards [1]. * Corresponding author, Tel.: +81 92 641 1151 ext. 2354; Fax: +81 92 641 8110. 0378-3782/95/$09.50 © 1995 Elsevier Science Ireland Ltd. All rights reserved

SSDI 0378-3782(95)01618-D

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In a pilot study, we previously described that, in the assessment of fetuses from 36 to 41 weeks' gestation, when observing penile length, the total duration of penile tumescence during the eye-movement period was significantly longer than that during the no-eye-movement period, thereby suggesting a strong in utero association between penile tumescence and the eye movement period [10]. Those results were in line with the same phenomenon during extrauterine life in the neonate, and also in the human adult, where nocturnal penile tumescence is closely related to rapid eyemovement sleep [4-91. There still remains, however, the problem of applying Karacan's criteria, originally established for evaluating human adults, to the fetus, in an identical fashion, in which after standardizing the range of penile circumference measurements in each case with minimum and maximum values at 0% and 100%, respectively, values less than 20% are considered flaccid, and those of 20% and greater indicate tumescence

[51. In this study, we therefore attempted to reveal, without prior knowledge of its existence, and depending solely on statistical analysis, whether the penis per se truly becomes tumescent and flaccid, in time sequence, in the human fetus at term under conditions of real-time ultrasound observation, and if so, to determine also the proportion of penile tumescence vs. flaccid duration during the examination period. 2. Material and methods

2. I. Fetal population Fifty male fetuses in cephalic presentation, from 36 to 39 weeks' gestation, fulfilling the following criteria were selected and examined once: (1) Gestational age was calculated from the first day of the last menstrual period (LMP) and confirmed by crown-rump length at 9-11 weeks' gestation to be within -4-2-3 days of the LMP deduced age. (2) Biparietal diameter, femur length and abdominal circumference were within the mean value -4- 1.5 S.D. for the corresponding gestational week by Japanese standards [15]. (3) Fetuses were without detectable anomaly. (4) Mothers were nonsmokers, with neither maternal complication nor incidence of drug administration. Thirty-eight of the 50 fetuses were excluded due to a lack of continuous ultrasound visualization of the penis: 20 cases reportedly had repeated sporadic 1- to 5-rain data-loss epochs and 18 had continuous data losses lasting 6-20 min. The remaining 12 cases were the subject of subsequent analysis. All mothers were cared for in the Maternity and Perinatal Care Unit, Kyushu University Hospital and gave informed consent to participate in this study. 2.2. Variable definition and data acquisition Real-time ultrasonographic equipment (Model SSA-270A, Toshiba, Tokyo) with a 3.75-MHz convex transducer was used. The study was conducted in a quiet room with the mother placed in the semirecumbent position, where a 60-rain examination was conducted after 15 rain of bed rest. The observational plane during the ultrasound examination was achieved with the transducer directed toward the penis so

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as to obtain an image of the penis longitudinally transecting the urethra at the midline of the penile shaft. Penile length was defined as that from the radix penis to the tip of preputium and used as a variable [10] (Fig. 1). By freezing the standard ultrasound image, we measured penile length once per minute at a given time, using an electric calliper, producing 60 measurements for each case. The condition observed at the m o m e n t of measurement was considered to be representative of that l-rain epoch.

2.3. Reproducibility of this experimental system A simulation experiment was made on five randomly selected fetuses (not included in the main frame study). The entire process was repeated 10 times on each fetus, with 10 penile length measurements obtained each time. The mean value for the coefficient of variation was found to be 4.1% (range 3.3-4.6%) (Table 1).

Fig. !. Ultrasound image for observation of the penis in a fetus at 37 weeks' gestational age. Curved and straight arrows show the tip of preputium and the radix penis, respectively; S, scrotum.

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Table 1 Reproducibility of ultrasound measurement of penile length Case

Number of measurements

Mean (ram)

S,E.M, (mm)

(S.D./mean) x 100 (%)

A B C D E

10 10 10 10 10

18.2 21.5 22.6 19.4 23.7

0.2 0,3 0.3 0.3 0.4

3.3 4.2 4.0 4.6 4.6

Mean value of coefficient of variation = 4.1 S.E.M., standard error of the mean; S.D., standard deviation.

2.4. Data processing and statistical analysis A scattergram of penile length vs. elapsed time from the start of observation was made from the data of each case. The scattergram was then analyzed using the least median of squares (LMS) regression analysis [13], yielding a regression line and standardized residual, defined as the LMS residual divided by the LMS scale estimate (aLMS) for each measurement. The 'outlying' and 'non-outlying' points, among the measurements herein, in each case, were defined as those with standardized residuals of > 2.5 and _