Many newly pregnant women wonder, "Is it twins?" Although twin pregnancies are more easily identified later in pregnancy, even at the time of the first missed period, or 4 weeks of pregnancy, there may be clues that more than one baby is on the way. Some signs are definitive, but others are only suggestive.
Gestational Sacs
The gestational sac is the first sign of pregnancy seen on ultrasonography. The gestational looks like an oval-shaped dark hole when you look at the ultrasound picture. At 4 weeks, the gestational sac is often visible on transvaginal ultrasonography, and if you're having twins, there may be two sacs, if the twins are fraternal, or non-identical. Identical twins develop in the same sac, so it may not be obvious that there is more than one embryo until the end of the fourth week or into the fifth week, when the yolk sac--the early source of the embryo's nutrition--may first be seen. If identical twins are present, two yolk sacs will be seen within the gestational sac, according to the Advanced Fertility Center of Chicago. The American Pregnancy Association states that transvaginal ultrasonography is able to diagnose a gestational sac and yolk sac approximately one week earlier than abdominal ultrasonography.
Human Chorionic Gonadotropin Levels
Levels of human chorionic gonadoptropin, or hCG, measure the amount of the hormone produced by the placenta. Women having twins generally, but not always, have higher hCG levels or faster rising hCG levels than those with singleton pregnancies. There is a wide range of normal hCG levels at 4 weeks; normal levels for a singleton pregnancy usually range from 17 to 119 milli-international units per milliliter (mIU/ml), the Advanced Fertility Center of Chicago explains. However, with twin pregnancies, they found the range at 4 weeks to be between 56 and 313 mIU/ml. A high hCG level isn't a definite indicator of twins, but it may raise suspicions, especially if the pregnancy was achieved through assisted reproductive technology, which is associated with a much higher rate of multiple births.
Subjective Symptoms
Women having twins often have more nausea, more frequent urination, sorer breasts and a higher level of fatigue than those carrying singletons because of the high level of pregnancy hormones such as estradiol and progesterone. Even at 4 weeks, when the first period is just being missed, women with twins may already have symptoms of early pregnancy. Another subjective but often accurate sign of a twin pregnancy is maternal intuition. Many twin mothers claim that they "had a feeling" or "just knew" they were carrying more than one baby very early in the pregnancy. As Labor of Love states, women know their own bodies best.
