I
AM a surprise twin.
I am nearly 42, so way before routine u/s, etc. Doc only every heard one heartbeat, and like others have said, the suspicion was that one of us was "hiding" behind the other.
Twins do NOT run in our family, alhtough my mom suspects she usually released more than one egg (judging from her v. heavy periods). Everyone believed Mom was having a big boy...except for her LLL leader and her mom, both of whom asked, "Are you sure it isn't twins??"
As for what happened in delivery, well, this was "back in the day", so mom was a little anesthetized (ether, I think). But as she tells it, she felt my sister (4lb13oz) come out and thought, "Hmm, that didn't FEEL like a big baby...". Then the doctor (between Mom's legs) looked at the nurse (behind her head), helpd up two fingers, and said "Dos!" (I don't know why he said it in Spanish, but that is Mom's story!). I was born 10 minutes after my sister, at 6lb3oz - so 11 pounds of baby total.
I can see how twins can be missed, or even how a woman can go entire pregnancy without knowing. Fetal and placental position both play a role in how much Mom feels; so does fetal movement (some babies are quieter than others). Mom's weight/amount of belly fat can affect what is seen/palpated from the outside. A history of irregular periods (PCOS, for example) and abdominal issues can contribute to thinking all those feelings in the belly are something else...Not every woman feels pregnancy the same way.
