Using interphase fluorescence in situ hybridization (I-FISH) to detect the transfer of infant cells during breastfeeding

Using fluorochrome-labeled probes for the X and Y chromosomes, fluorescence in situ hybridization (FISH) was used to test for the presence of male cells in the milk of women breastfeeding male babies. After breastfeeding, the women wiped one breast and collected a test sample. Wiping efficiency was evaluated in 2 mothers by running a solution over the nipple after wiping. Cells were collected from both the milk and the rinse samples by centrifugation. The cells were fixed to glass slides for hybridization with the X and Y probes. Two cell populations were observed: small female (XX) cells from the mother, and large epithelial cells that were shown to be male (XY), presumably from the baby's mouth. Results varied from 0 to 175 male cells detected per milliliter of breast milk. This finding suggests that small molecules, including possible pathogens, in a baby's mouth, might also be passed directly into the breast.