DNA testing in infants is a non-invasive procedure used for paternity confirmation, forensic analysis, or genetic screening. These tests typically rely on collecting the infant’s DNA, usually through a cheek swab of the buccal cells inside the mouth. When testing a breastfed infant, a common concern is the potential for the mother’s breast milk to interfere with the accuracy of the results. An inconclusive or inaccurate test can lead to significant diagnostic or legal complications.
The Potential for Maternal DNA Interference
Breast milk itself does not change an infant’s unique genetic code, which is determined at conception. However, residual breast milk inside the infant’s mouth during sample collection can introduce contamination. The primary issue is not the liquid milk, but the maternal cells naturally suspended within it. This contamination is particularly significant when using the common buccal swab method, which collects cells from the cheek lining.
If a cheek swab is performed too soon after nursing, it picks up the infant’s cells along with the residual maternal cells from the milk. This creates a mixed sample containing two distinct DNA profiles, complicating the laboratory’s ability to isolate the infant’s profile. One study demonstrated that maternal cells were present in almost half of the samples collected within five minutes of breastfeeding. This contamination does not alter the infant’s DNA, but it compromises the sample quality, potentially leading to an inconclusive result and requiring the test to be repeated.
Understanding the DNA in Breast Milk
The reason breast milk can carry the mother’s DNA lies in its cellular composition. Breast milk is a complex biological fluid containing living maternal cells, not just free-floating DNA. These cells primarily consist of epithelial cells, which line the milk ducts, and leukocytes (white blood cells) from the mother’s immune system.
Each maternal cell contains a full copy of the mother’s DNA within its nucleus. When the infant feeds, these cells are deposited directly into the oral cavity. A buccal swab collects the infant’s cheek cells along with these deposited maternal cells. The resulting sample is a mixture of two separate genetic profiles, which is challenging for the laboratory to analyze, especially in tests like paternity testing.
Best Practices for Accurate Infant DNA Testing
Mitigating the risk of maternal DNA contamination relies on careful preparation before sample collection. The most effective strategy is ensuring a sufficient waiting period between the final feeding and the collection of the cheek swab. Research indicates that waiting at least 60 minutes after feeding significantly reduces the presence of maternal cells in the infant’s mouth. Many testing laboratories recommend waiting an hour or more to ensure the mouth is clear.
In addition to timing, physically cleaning the infant’s mouth is recommended before swabbing. Gently wiping the inside of the cheeks and gums with a sterile cotton swab or rinsing the mouth with sterile water helps remove any remaining breast milk residue. This simple step decreases the number of contaminated samples. While laboratories employ specialized techniques, such as differential lysis, to process contaminated samples, proper preparation ensures the sample is clean and the test results are accurate on the first attempt.