How can the mother get to know that she is having twins?

Q: My early pregnancy (6th week) ultrasound scan report says - single intrauterine gestational sac with small fetal pole and single double decidual rim of gestational sac. Does this indicate that it is a single fetus or multiple fetuses? In general, when and how do we find out whether its a single fetus or twins?

A:This ultrasound report suggests a likelihood of a single baby. However, very occasionally a twin may not be picked up upto 10 weeks from the first day of the last menstrual period. Most (but not all) twins are picked up on ultrasound by 6 weeks of pregnancy.