There is a myth that pineapple is a sour and hot food that can induce uterine contractions and lead to miscarriage or preterm labor. Therefore, it is believed that pregnant women should not consume pineapple during pregnancy.
However this is not true.
A cup of ripened pineapple pieces or a glass of juice is not harmful during pregnancy. Pineapple has vitamins, minerals, fiber, and water. It contains high dietary fiber and low saturated fats. It contains Vitamin C, B1, B6, and Folic acid. It contains a substance called Bromelain that helps reduce blood pressure. Bromelain is said to have a relaxing effect on the cervix and therefore the myth that it can cause miscarriage and preterm labour. But the bromelain content in one moderate helping is not going to be enough to cause any such effect.
There is no harm in consuming Pineapple during pregnancy if you enjoy the fruit. As it is an acidic fruit, it is better to avoid it in case you have acidity.