If you're wondering whether or not you're carrying twins (or more!), you're not alone. With the incidence of twins increasing dramatically over the past two decades, many expecting moms wonder if two babies might be on the way. Trying to Conceive: Are You Ahead of the Game? Age matters. One reason for the increased incidence of multiple births in the United States is the trend toward delaying pregnancy. The incidence of twins increases for women over the age of 35 and even more if you are over 50. To put it in perspective, your chance of giving birth to twins if you are under 25 years of age is less than half of what it would be after the age of 35. The odds of twins increase with the use of assisted reproductive technology. Both ovulation-inducing drugs (infertility treatment) and in-vitro fertilization increase the odds of having twins. Between 1973 and 1990, twin births increased at twice the rate of singletons, and triplet and higher order births increased at seven times the rate of singletons. (Obstetrics and Gynecology 1994; 84:101-6) Twins may run in your family. Even before diagnosis of pregnancy, you may suspect that you are at an increased risk of conceiving twins. Fraternal (dizygotic) twins may run in the family, and, contrary to popular belief, they do not necessarily skip a generation. If your mother or grandmother had twins, you may be carrying a gene that causes you to release more than one egg at a time, making it more likely that you will have twins. 9 Signs You May Be Pregnant with Twins 1. You just feel you're carrying more than one baby. Don't disregard intuition or dreams. Some mothers of twins (or higher order multiples) say that they knew right from the start that they were carrying more than one baby. 2. You experience more nausea and/or morning sickness. If you are having more than one baby, you may also have an elevated hCG level. Higher levels of hCG also make it more likely that you will have bouts of morning (or all-day) sickness. 3. Other normal pregnancy symptoms may be exaggerated. Many women -- but not all -- who are pregnant with twins have more intense pregnancy symptoms, likely due to the extra hormones circulating through their system. You may find that your breasts are very tender, you have to urinate frequently, you are hungry all the time and you are very tired. In the second trimester, you may experience difficulty catching your breath, swelling (edema) of the hands and legs, an unusual rate of weight gain and abdominal enlargement and excessive fetal movement. Anemia or low iron (decreased hemoglobin) is also common with twin and multiple pregnancies. 4. You gain weight rapidly in your first trimester. A higher than average weight gain in the first trimester may be your first clue that you're carrying more than one baby. If you're eating well, don't be concerned: A study in the American Journal of Obstetrics and Gynecology stressed the importance of early weight gain for twin pregnancies, since weight gain in the first two trimesters was found to have the greatest impact on birth weight. (American Journal of Obstetrics and Gynecology 1998;179:1155-1161) 5. You measure large for gestational age. At your first exam you may be told that your uterus is "large for dates." If your last menstrual period indicates an eight-week gestation, your uterus may feel more like 10 to 12 weeks. This may prompt your care provider to request an ultrasound. As your pregnancy progresses, if you are carrying more than one baby, your fundal height (uterine measurement) will consistently measure large for gestational age. A term uterus, with one baby, may reach 38 to 40 centimeters in height, measured from the pubic bone, while a term twin pregnancy may exceed 48 centimeters. 6. You are told that you have elevated levels of AFP. Levels of alpha fetoprotein (AFP), a protein released by the baby as it grows and found in the mother's blood, can be elevated when there is more than one baby. (It can also be elevated for other reasons, such as neural tube defects.) Normally this simple blood test is given 16 to 18 weeks after your last menstrual period. Alpha fetoprotein testing detects over half of all twin pregnancies. 7. You are told you have rapidly rising hCG levels. Human Chorionic Gonadotrophin (hCG) is a hormone produced by the fertilized egg and by the chorionic villi. It is needed to maintain the pregnancy until the placenta develops. It can be detected in your blood or urine even before you miss a period. Normally in a singleton pregnancy, blood (serum) concentrations of hCG rise rapidly during the first weeks, doubling every two to three days. Levels of hCG can be even higher with twin or multiple pregnancies. 8. Your provider hears two fetal heartbeats. Two separate heartbeats can be distinguishable with a Doppler in your care provider's office by around 12 weeks. At around 28 weeks, it may be possible to differentiate two fetal heads and multiple small parts when doing an abdominal exam. 9. You have a positive ultrasound. If you believe you are indeed pregnant with twins, an ultrasound can be performed quite early in pregnancy. With a skilled ultrasonographer, two gestational sacs, two embryos and two distinct fetal heartbeats can be seen six weeks after the first day of the last menstrual period. Many twins have been diagnosed as early as five weeks -- when you're just one week late for your menstrual period. 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