Interesting question...

[alhardin]

Ok if the placenta does not 'take over' until 12 weeks, and the baby is safe from what we eat and drink...then why do they say, the first few weeks are the most important for taking care of yourself because it's the most important time in fetal development? I have always wondered that, but never gave it much thought. Any ideas? :dunno:

[froggie83]

good question. i will be stalking to see if someone has an answer!

[kellyowens]

"The placenta takes over" means that it takes over progesterone production :). Prior to that the corpus luteum is in charge of productions...after the placenta takes over the ovaries go dormant.

The first 6-10wks are the most important because teratogens can cross the placental barrier and cause developmental problems in the embryo due to the rapid rate of growth and formation of all the baby's vital systems.

So the placenta is definitely functioning (maternal/fetal circulation begins around week 6) but it's not producing progesterone until sometime between 10 and 14wks :).