Maternal cell contamination of buccal smear samples in nursing neonates

Buccal smear analysis is a non-invasive method which is being popularized by new fluorescence in situ hybridization (FISH) techniques. It is frequently used for gender identification and detection of sex chromosome aneuploidy in neonates. We attempted to determine whether or not buccal smears of nursing infants can be contaminated by maternal cells from breast feeding. FISH involving centromere specific directly labeled, multicolor probes for chromosomes X, Y and 18 were used for analysis of buccal smear samples. Buccal smear samples from 22 breast fed and 20 formula fed male neonates were analyzed in a blinded fashion. Twenty-seven percent of samples from breast fed infants had some (0.5-2.5%) XX signal pattern while the samples from formula fed infants had no XX signal pattern (difference statistically significant, p < 0.02, at 95% confidence interval). Our results indicate that breast feeding can cause maternal cell contamination of buccal smear samples that can lead to misinterpretation of results involving FISH analysis or other DNA based diagnostic studies. We have also modified the FISH technique to suit the neonates.