Your midwife may recommend an early scan at between six weeks and 10 weeks if you have experienced bleeding.
You may also be offered an early scan if you've had a previous miscarriage.
Pretty darn accurate, as it turns out: One recent study found that 98 percent of the time, the ultrasound tech correctly predicted the gender of the baby.
"The external genitalia -- the vulva or penis and scrotum -- are not actually external until about 13 weeks." You may want to wait until your later ultrasounds, such as your 20-week anatomy scan, for a more definitive answer.
"The accuracy of the ultrasounds increases as gestational age advances," says Bart Putterman, M.
Finding out about having twins early in pregnancy also gives you more time to prepare for the birth and for your doctor or midwife to plan your care.
Knowing about twins early is also useful if you want to have screening for Down syndrome.
Ultrasound may be a key tool for doctors to determine the health of a fetus, but for many expectant parents, it's key for another important (and exciting) reason: It can clue you in on whether you're expecting a boy or girl!