Richmond, Va.

FOR most of human history, a woman who became pregnant after sleeping with more than one partner had no way of definitively knowing the identity of the man with whom she had conceived. Likewise, a man whose lover became pregnant had no way of knowing for sure whether his or another man’s DNA was gestating inside her.

Since the 1970s it has been possible to genetically link a father and his baby with increasing levels of accuracy. Then, a test using amniotic fluid let us test a baby’s DNA before birth, but the procedure increased the risk of miscarriage. Now a prenatal blood test has made the process far easier. Since a small amount of fetal DNA is present in a pregnant woman’s blood, the pregnancy can be genetically linked to her partner through a simple blood draw from the woman’s arm.

One of the potential ramifications is that men might be called upon to help support their pregnant lovers before birth, even if the pregnancy is ultimately terminated or ends in miscarriage. They might be asked to chip in for medical bills, birthing classes and maternity clothes, to help to cover the loss of income that often comes with pregnancy, or to contribute to the cost of an abortion.

Of course, plenty of men already treat the costs of pregnancy as a shared responsibility. But some do not, leaving the woman to shoulder the burdens alone.