This question originally appeared on Quora. 
Answer by Linda Geddes, Author of Bumpology: The Myth-Busting Pregnancy Book for Curious Parents-To-Be
You might think that pregnancy is an experience that only women can appreciate, but somewhere between 11 and 50% of men are thought to experience symptoms of sympathetic pregnancy, or couvade syndrome. The most common symptoms include appetite loss, toothache, nausea and anxiety, and these symptoms tend to peak during the third month of pregnancy at around the time when many women are suffering the horrors of morning sickness. Whether couvade syndrome is a real phenomenon remains up for debate; very little research has been done on it, but those studies that do exist suggest men are more likely to suffer symptoms if they are highly involved in their partner's pregnancy, or in preparing for the birth of their child.
Couvade syndrome aside, men also experience other hormonal changes towards the end of their partner's pregnancy and once their child is born. One is a rise in the hormone prolactin, best known for its role in triggering breastfeeding in women. Studies suggest that men with the highest levels of prolactin when their babies are six months old are more likely to engage with their child. Levels also shoot up when men hear their baby cry.
Testosterone levels drop, possibly making dads more attentive to their family's needs. A different study found that men with higher testosterone levels were less likely to give their children attention, while those with low testosterone expressed more sympathy and a greater need to respond when they heard their baby cry. Levels of the so-called cuddle chemical, oxytocin, also increase in new dads and this too seems to relate to paternal behavior. Dads with higher levels of oxytocin played with their children more often and seemed more attached to them than those with less of the hormone. But it's not a one-way street -- playing with babies and spending time interacting with them will also boost oxytocin levels in men, so the more dads engage with their kids the more their paternal instinct is likely to kick in.
Fathers also are not immune from the suffering from the blues when a baby enters their life. Postnatal depression is estimated to affect between four and 25% of men in the two months after the birth of a child, although its onset may be more gradual than in mothers and therefore less likely to be detected. Whichever parent suffers from depression, it can impact the baby's emotional development, so couples should not feel embarrassed to ask for help.