Pregnancy changes a woman's body to such a significant extent, it's no wonder that some women experience unusual or unanticipated symptoms at one time or another during their nine months. While tingling hands may not be one of the classic signs or symptoms of pregnancy, they are nevertheless relatively common, and have a variety of causes.
Carpal Tunnel Syndrome
One of the most common causes of hand tingling during pregnancy is carpal tunnel syndrome, which results from swelling of the carpal tunnel, a tube in the wrist through which nerves pass. Pregnant women, explains Dr. Miriam Stoppard in her book, "Conception, Pregnancy and Birth," experience vastly increased fluid volume as they produce additional blood. This can lead to edema or swelling of the extremities as fluid leaks out of the small vessels and into the space surrounding cells. Swelling can then compress local tissues---if the swelling occurs in the hands and arms, for instance, compression of the carpal tunnel can result. This leads to pain and tingling in the hands and fingers. Many women find that sleeping with the hands and lower arms elevated helps relieve symptoms.
Low Blood Pressure
During the early months of pregnancy, the uterus and breasts grow more blood vessels than ever before. This increases the capacity of the vascular system, and while blood volume eventually increases as well, there is a period of time during early pregnancy in which blood volume is low compared to the volume of the vessels. This results in low blood pressure, as Heidi Murkoff and Sharon Mazel explain in their book, "What To Expect When You're Expecting." Low blood pressure can have a number of effects, one of which is reduced blood flow to---and reduced blood return from---the extremities. Tingling hands are a potential result, for the same reason that a compressed arm or foot "falls asleep." When tissues are denied adequate blood flow for a period of time, nerves respond with the sensation of numbness and tingling. Squeezing the hands into fists and moving the arms can help low pressure-related tingling of the hands.
Dr. Raymond Poliakin, in his text, "What You Didn't Think To Ask Your Obstetrician," notes that among the hormones produced by the body during pregnancy is one designed to loosen joints. This hormone, called relaxin, helps prepare the pelvis for passage of the baby during delivery by relaxing the ligaments that hold the pelvis together. Relaxin, however, is not confined to the pelvic joints, and can act upon joints all over the body. Pregnant women therefore become more flexible than they were pre-pregnancy. One result of loosened, joints, however, is that nerves running through or near joints may become compressed as bones shift away from their pre-pregnancy positions. Compressed nerves lead to tingling sensations. Since pregnant women generally have to sleep on their sides---bellies preclude stomach sleeping, and the later months of pregnancy are not conducive to back sleeping---it's common for the shoulder joints to shift during sleep, and for nerves in the shoulders to become compressed, leading to tingling hands. Softer mattresses and frequent changes of position during sleep can help alleviate symptoms.