Pregnant women produce more progesterone especially during the first trimester. Progesterone is also known as a relaxing hormone and can make you sleepy. Progesterone also increases production of GABA a neurotransmitter which is also known to induce sleep. Progesterone in other words is a sleep promoting hormone.

But some women during pregnancy experience sleeplessness and restless nights. This could be due to changes to the body and fluctuating hormone levels. If it the first trimester she may be troubled by morning sickness and also increasing progesterone which decreases blood pressure and could make you feel very tired. Increased frequency of urination could also be because of the increasing size of the uterus pressing on the urinary bladder which increases the urge to urinate frequently. As you head into the second trimester these symptoms may come down and this is most likely the most comfortable part of your pregnancy. 

You may be troubled by increasing frequency of urination and frequent nighttime awakenings in third trimester, due to increasing pressure of the expanding uterus on the urinary bladder and may also make you uncomfortable sleeping because of the sheer size of the abdomen and physical exertion and stress. Anxiety of being a mom can also be one of the factor for lack of sleep especially as you get closer to  labour and delivery. 

Tips for good night sleep