I’ve been asked many times, mostly by worried pregnant mothers or potential baby fathers if a fetus’s DNA can be changed or effected by either another man’s semen while she is pregnant or from her sexual activities with previous partners.
The short answer is no.
There is a false belief that women absorb and retain the DNA of every man they have unprotected sex with. This belief has been spread through some articles, but stems from a 2012 research project that showed that the brains of some autopsied women had male DNA. Some who heard this quickly jumped to the conclusion that they must have received this male DNA through sperm.
The truth is, this is called microchimerism and the explanation for the male Y chromosome being found in some female brains is not really that complex.
When women become pregnant, they play host to another human with its own set of DNA. Some of this DNA gets absorbed through the placenta and remains with the woman for the rest of her life. If she has any male children then she will absorb some male DNA which explains why some of the women autopsied (aged 32 to 101) had male DNA in their brains even decades later.
The DNA a mother inherits from her child is often up to 10% of the free floating DNA in her blood stream. Often call foetal origin cells, they have also been found in the mothers skin and all major organ including the heart.
Blood Transfusions and Organ Transplants
When we receive blood transfusions or organ transplants, we are also receive some DNA from the donor. This is known as medical chimerism and is something the medical world has been aware of for a long time. If a woman receives a transfusion or transplant from a male, it is likely she will also absorb some male DNA.
Having an Older Male Sibling
If a woman has an older brother, the chances are her mother has absorbed some male DNA from him during her pregnancy and also passed it along to her daughter. This explains why some of the women autopsied who did not have any male children, blood transfusions or transplants, still had the presence male DNA.
Research suggests that having male DNA passed on to these women doesn’t affect them as far as femininity goes, but that it could have several beneficial effects:
- Lower risk of some cancers
- Longer life span
- Better tolerance of successive pregnancies
- Decrease risk of Alzheimer’s
- Diminished symptoms of rheumatoid arthritis
So while many women have the presence of male DNA, it’s not because they were having unprotected sex. They do not carry the DNA of ex-lovers and thankfully are not bonded to them for life, however, they will be bonded even on a cellular level with their children til death.