Volleyball is a great sport to help you stay active. It provides a good cardio workout and strengthens your agility, exercising both your upper and lower body. However, it is a game that requires a lot of movements and jumping, and there is an increased risk of falling while trying to squash that ball down over the opponent's net.
Risk of Falling
Early in pregnancy, the uterus does not yet interfere with your activities. You can still do everything you did before getting pregnant because your balance and gait are still good and you haven't gained any substantial weight just yet. As your pregnancy progresses and as your belly gets larger, your center of gravity shifts, and jumping and fast movements can lead you to lose your balance and fall. When you fall, you can injure both the baby and yourself.
Chance of Contact/Collision
There are certainly other sports that are more high-contact such as football, soccer, and wrestling for example, but even in volleyball, you could potentially collide with other players. Severe contact can cause the uterus to be injured and/or placenta to tear away from the uterine wall, a condition known as placental abruption.
With volleyball's frenetic pace and since it is often played on the beach or out in the sun, heat exhaustion can quickly occur. While your bodily fluids are building up in order to nourish you and the baby, you still need to replenish regularly and often. Water is the best option; energy and sports drinks contain added caffeine and sugar.
Pregnancy hormones tend to loosen joints so your gait may not be what it used to be. Progesterone may be partly to blame. Progesterone works to loosen ligaments for birth, but it cannot dedicate that work to the pelvic region only. Loose ligaments can lead to hyperextension of the back, knees, and hips.
Remember that pregnancy only lasts for a short nine months and you can always take up your favorite sport again once the baby is born.