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    Neonate with bilateral breast enlargement

    The Case

    A 10-day-old female infant presented to the clinic for a weight check. She was feeding well, but her mother was concerned about her newly swollen breasts.

    The infant was born at 40 weeks’ gestational age via uncomplicated spontaneous vaginal delivery to a gravida 1/para 1, 24-year-old mother. The mother was positive for group B Streptococcus and received peripartum antibiotics, so both mother and baby were observed in the hospital for 48 hours. The patient's birth weight was 3209 grams; Apgar scores were 8 and 9 at 1 and 5 minutes, respectively. At discharge, her weight was 3008 grams. Her total serum bilirubin was 6.5 mg/dL, and she was breastfeeding well. Her chest appearance was normal.

    In clinic, the infant's vital signs were normal, and she had normal weight gain. Upon review of systems, the infant was breastfeeding well with no fussiness or fever. Physical examination was significant only for engorged breast buds that were symmetric, erythematous, and nontender (Figures 1 and 2). The breast buds were 6 cm in diameter with nipple indentation due to engorged areolae. With gentle pressure, scant white milk was expressed. There was no increased heat, nodularity, cording, or tenderness to the breast tissue. There was no vaginal discharge, axillary hair, pubic hair, or acne found on examination. Physical exam was otherwise normal.

    Differential diagnosis

    Newborn gynecomastia is most often a natural reaction to falling maternal estrogen levels toward the end of pregnancy. However, the clinician must consider other etiologies (Table). Certain drugs can cause gynecomastia when passed through maternal breast milk or the placenta.1-4 Other less-common etiologies for gynecomastia in newborns include mastitis, lipomas, and breast cancer.5-8

    Drugs that alter the baby’s estrogen and androgen levels may induce gynecomastia and, in the case of a pregnant or breastfeeding mother, may be passed from mother to child, triggering breast enlargement. Estrogens may stimulate breast growth by increasing prolactin production by the pituitary gland.1

    Recommended: Rapidly growing nodule on infant's posterior thigh

    Antiandrogens also can cause gynecomastia. For example, antifungals (ketoconazole and metronidazole) and H2 antagonists (cimetidine and ranitidine) have antiandrogenic effects, most importantly on testosterone.2 Testosterone normally functions to inhibit breast tissue proliferation, so drugs that reduce its synthesis may cause gynecomastia.1 Spironolactone is another drug that affects steroid balance. It competitively binds aldosterone receptors to induce its diuretic effect, but it also blocks androgen receptors. Cytotoxic chemotherapy drugs have been associated with gynecomastia, attributed to decreased production of testosterone.2 Prolonged topical use of lavender oil or tea tree oil may cause breast enlargement as well, although the mechanism for this effect is not well understood.3

    Placentophagy, or the consumption of placentas, is uncommon but becoming increasingly popular, so it should be noted if a mother of a baby with gynecomastia is partaking in this practice. According to advocates for placental consumption, it can speed up uterine recovery, prevent postpartum depression, and increase milk production in mothers. Although very little scientific research about the effects of placentophagy on nursing babies exists, the placenta produces estrogen and lactogen, which induces breast changes in the mother to prepare for lactation.4

    In this case, a careful history was obtained from the mother, and she did not use any gynecomastia-inducing drugs during her pregnancy or while breastfeeding. There were no external causes that could explain the infant’s breast enlargement.

    NEXT: Differential diagnosis

    Vanessa Rave, BA
    Ms Rave is a student in the medical master’s degree program at Eastern Virginia Medical School, Norfolk, Virginia.
    Gretchen Brantley, MD
    Dr Brantley is a general practice pediatrician at Piedmont Pediatrics in Charlottesville and Crozet, Virginia.


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