http://biblos.com/luke/1-31.htm
Luke 1:31 And behold, you will conceive in your womb and bear a son, and you shall call his name Jesus.
http://concordances.org/greek/4815.htm
syllempse
Short Definition: I seize, apprehend, become pregnant
Definition: I seize, apprehend, assist, conceive, become pregnant.
the term dates to the 13th-14th centuries and was understood as “to take seed into oneself”.
Which is not what the term means today. Conception meaning - “sperm and egg unite” doesn’t come about until much later.
Applying what the term means today to what it meant when it was written is incorrect.
“become pregnant”, absolutely. Conception!= sperm and egg unite - no.