Most pregnant women wonder, at some point, whether they're having twins. Subjective signs, such as increased nausea or weight gain, aren't reliable indicators of a twin pregnancy. Ultrasound can generally detect a twin pregnancy very early, around the 5th or 6th week of pregnancy, or 4 weeks after conception. If you think you might be having twins, talk with your doctor about confirming your suspicions.
If your doctor does a blood test for pregnancy, your human chorionic gonadotropin, or hCG, level might be higher than expected for how far along you are if you're carrying twins pregnancy. This doesn't prove you're having twins, however, since hCG levels vary considerably. While some women experience more severe nausea and vomiting while carrying twins, intense morning sickness can also occur when pregnant with a single baby. Uterine size greater than expected for how far along you are in your pregnancy could also indicate twins, although this often isn't measured until 16 weeks of pregnancy or later. Additionally, there may be other medical reasons for a larger than expected uterus.
Ultrasound is the most accurate and earliest way to diagnose a twin pregnancy. However, a twin pregnancy diagnosed very early in the first trimester may not lead to the birth of twins. The Society of Obstetricians and Gynaecologists of Canada cautions that only one fetus develops in as many as 50 percent of twin pregnancies diagnosed in the first trimester. By week 10, your doctor might be able to hear 2 heartbeats.