a maternal blood sample are the most common ways to determine this, and the appropriate dose of RhoGam is calculated based on this information.
* There are also emerging tests using Cell-free DNA. Blood is taken from the mother, and using PCR, can detect fetal DNA. This blood test is non-invasive to the fetus and can help determine the risk of HDFN. Testing has proven very accurate and is routinely done in the UK at the International Blood Group Reference Laboratory in Bristol.

Paternal blood