There is no universal or scientific reason why a husband should not get a haircut or shave during his wife's pregnancy. Such a belief or tradition might be based on cultural or personal beliefs rather than any medical or logical reasoning.
In some cultures or traditions, it is believed that avoiding personal grooming during pregnancy can bring good luck, protect the health of the unborn child, or promote the well-being of the mother and baby. These customs are often deeply ingrained in certain societies, and people may follow them out of respect for tradition and to show solidarity with their pregnant partner.
However, it's essential to remember that these practices are not based on scientific evidence. Pregnancy does not have any direct impact on a husband's grooming choices, and maintaining personal hygiene is generally recommended for overall health and well-being.
Ultimately, whether a husband chooses to follow such customs or not is a personal decision. It is essential for couples to communicate openly and support each other's choices during pregnancy while also considering their individual beliefs and cultural backgrounds. As always, consulting with healthcare professionals for evidence-based advice on pregnancy and prenatal care is crucial for the health and safety of both the mother and baby.