Although previous generations often were surprised by a multiple birth, today most parents-to-be learn the news fairly early. A routine first-trimester ultrasound can detect most multiples.
(Sometimes a twin pregnancy that is identified very early is later found to have only one fetus. This is called "vanishing twin syndrome," and its cause is not well understood. The surviving twin generally is not harmed.)
Other factors can alert a health care provider that a woman may be expecting twins or more. These include:
A health care provider who suspects a multiple pregnancy most likely recommends that the woman have an ultrasound to find out for sure.