Multiple births originate from the release and fertilization of more than one egg, or the division of one egg very early in its development. Twins occur in about one out of 90 pregnancies, while triplets are found in only one out of 9,000. Factors that increase the likelihood of a multiple birth include a strong family history of twins or multiple births, age, ethnic origin, and previous births. The use of fertility drugs and 'in vitro' (in-VEE-tro) fertilization have also increased the incidence of multiple births. A multiple birth may be suspected if there's an extraordinary weight gain, a rapid increase in uterine size, a large amount of fetal movement, and a strong family tendency for multiple births. Multiple births can be diagnosed as early as five to seven weeks through the use of ultrasound. While exciting, a multiple pregnancy is also more stressful on your body. Early diagnosis allows for close monitoring to assure the mother's caloric (kah-LORE-ick) intake is sufficient and to guard against anemia (a-NEE-mee-uh) and premature labor. In general, you'll need to see the doctor more often during your pregnancy. Multiple birth pregnancies frequently deliver before term. You may have more physical discomfort and tire more easily, because of the extra weight. For this reason, bed rest may be prescribed in the third trimester. If you may be predisposed to multiple births or suspect you're carrying more than one baby, consult a doctor or prenatal care provider for more information.