Determining whether your pregnant with multiples is not easy, but with medical technology today it is a lot easier than before. Let's put it this way, our mothers’ generation had a lot more surprises at birth than we do now!
Most multiple births are not noticeable during the first trimester. This is because your body does not experience as much change as it does during the second and third trimesters, though many mothers who are pregnant with multiples do tend to report more severe cases of morning sickness and are more likely to experience HG.
Multiples are usually suspected during the second trimester, because the mother often gains more weight than is normal for that stage of pregnancy (though sometimes this weight gain can result from reaching into the cookie jar one too many times!). More importantly, the mother’s uterus expands more than it should for that stage of pregnancy if she is pregnant with multiples. However, a quantitative hCG blood test could reveal the possibility of multiples during your first trimester.
Your physician will confirm or throw out these suspicions using an ultrasound in which he/she will be able to see if more than one head is present in your womb. Listening for more than one heartbeat is not a reliable method of determining if you are pregnant with multiples, because a baby’s heart beats so rapidly that sometimes one heartbeat can sound like two or two heartbeats can sound like one.
Another indication that you may be carrying multiples is if you have previously had a set of multiples, because your chances of having a multiple birth quadruple if you've had multiples before!