The techniques of the Ballard scale for physical examination of estrogen responsive tissues in infants are readily taught, and breast bud diameter is validly assessed. Vaginal cytology specimens are easy and atraumatic to collect. All examinations appear precise enough for research protocols.
Not all tissues that show developmental response to estrogen reverted when maternal estrogen was withdrawn at birth. Although breast tissue was maximal in newborns and smaller in older children, external genitalia showed few differences by age. Vaginal bleeding, from withdrawal of maternal estrogen’s trophic effect on the infant’s endometrium, was not observed. Infants synthesize some estrogen, and it may mitigate the effects of withdrawal of maternal estrogen. Vaginal wall cells are responsive to maternal estrogen, appear to lose that effect by 1 month, and then may respond both to estrogen synthesized by the girl and to soy formula. We looked for milk secretion in infants because we thought exogenous estrogen might inhibit prolactin’s promotion of milk synthesis (Guyda and Friesen 1973
), but milk secretion was rare. We propose that a longitudinal set of physical examinations of girls aimed at detecting the effects of exogenous estrogen should be performed weekly to fortnightly for the first 1–2 months. Vaginal cytology specimens need to be collected for > 6 months. Milk secretion or vaginal bleeding should be asked about because they have a plausible endocrine basis, but will be infrequent.
Our physical findings, like those of others (Alexander et al. 1992
; Donovan et al. 2007
), show more variability than Ballard reported (Ballard et al. 1979
) in term infants. Ballard reports labia majora cover the clitoris and minora at term, which we saw in all girls older than 17 days but only in half of the younger girls. Ballard saw deep scrotal rugae at term, but most of our boys had “good” rugae, only one had “deep” rugae.
We measured testicular volume in infants 48 hr to 6 months of age using orchidometer beads that were smaller and in smaller increments (0.5 mL) than the norm. Mean testicular volume (0.7 mL) in our younger age intervals was less than others report, but was similar by 6 months of age (1.04 mL). Average testicular volume from tissue sections in 1-year-olds was 1.1 mL (range 0.3–1.9 mL) in autopsy material from 36 Danish children who died accidentally (Müller and Skakkebæk 1983
). Orchidometric assessment in Taiwanese newborns showed mean volume of 1.3 ± 0.3 mL (Chin et al. 1998
). Chemes (2001)
and Sak et al. (1993)
reported infant testicular volumes of approximately 1 mL. In a small but longitudinal study, Cassorla et al. (1981)
measured testicular volumes with orchidometer beads of the same sizes as ours monthly in 10 U.S. boys from birth to 6 months of age. Volume increased from birth (1.1 mL) to 2–3 months (2.0 mL), and then declined (1.5 mL at 6 months) (Cassorla et al. 1981
). The increase is plausibly related to the reported peak in testosterone at 2 months (Grumbach 2005
). Assuming the peak occurs regularly, detecting it may require the smaller variability in longitudinal data, and will require monthly, or more frequent, exams.
Ballard reported that term infants of both sexes had breast buds of 5–10 mm diameter and palpable adipose breast tissue (Ballard et al. 1979
). Among 21 term infants followed by McKiernan and Hull (1981)
, mean breast bud diameter was 9 mm at birth, 13 mm at 2 weeks, and receded to 10 mm at 1 month, with breast buds in girls larger than in boys. We did not observe an increase in breast bud size postnatally nor a sex differential, and can offer no explanation for these differences. Among 1,126 Danish infants with median age of 3 months, 79% had breast buds, girls more often than boys; buds were larger in girls (5.7 vs. 4.9 mm) and associated with endogenous estradiol levels (Schmidt et al. 2002
). McKiernan and Hull (1981)
observed that most infants still had palpable adipose breast tissue at 6 months, as did ours, and that most 1-week-old term infants had some milk secretion, but ours did not.
We know of no other studies that report vaginal maturation index from vaginal wall cells in infants, although it can be used both in the diagnosis and the evaluation of treatment for precocious puberty in girls (Comite et al. 1981
), and should have a shorter response time than, say, breast size. The components of vaginal maturation index are usually used as a measure of estrogen effects in adult women (Hammond 1977
; van der Laak et al. 1999
). In a “normal child,” one would expect almost 100% parabasal cells, few intermediate, and 0% superficial cells, for a vaginal maturation index of nearly 0%, whereas a peripubertal girl may have a virtually no parabasal, 90% intermediate, and about 10% superficial for a vaginal maturation index of about 55%. Infant girls’ cells responded as expected to their in utero
exposure to maternal estrogen (Farage and Maibach 2006
); at 1 month, this effect was not apparent. Older girls had higher vaginal maturation index values, which may represent the effect of their own synthesis of estrogen. Older soy-fed girls had somewhat higher vaginal maturation index values than girls of the same age on other diets. This observation, though perhaps a chance occurrence, is plausible and deserving of follow-up. We recommend use of vaginal maturation index in infant girls. A possible parallel measure in boys, called the urocytogram (Preeyasomba and Kenny 1966
), exploits the hormonal responsiveness of urethral cells from spun urine. We did not evaluate this end point but now would consider using it.
Our study, although small and primarily cross sectional, suggests choices among responses for further studies. For example, our data suggest that genitalia do not vary much by age and thus will not respond to exogenous estrogen with delayed regression. Breast tissue did appear responsive, as did vaginal wall cells. Withdrawal vaginal bleeding and breast milk are worth noting but are infrequent. This study was a pilot and too small for reliable inference about feeding regimens. Our results indicate that these methods can be used validly and repeatably in infants; they may allow more direct, interpretable investigations of the infant’s response to estrogen-like compounds.