Chemical Agents mostly harmful only after the first trimester? (food for thought)

Here's some info regarding the "technical" aspects of the placental
circulation. I discovered this info after a research I made because I
was concerned about my alcohol consumption during the 3rd week after
conception.
These findings (note: I'm not a doctor or an MD, I am not related by
any means to the medical profession)may imply that during the first
trimester the embryo is relatively protected, though this is by no
means a suggestion that alcohol may not be harmful to a fetus, this
message is just some "food for thought".

1."All of this activity, remodelling the maternal host's arterial
supply to the placenta, means that just a trickle of maternal blood
gets to the feto-maternal interface in the intervillous space for the
first three months of pregnancy. If everything is developing normally,
a transvaginal ultrasound will demonstrate an absence of flow through
the placenta in a healthy pregnancy. (Remember,you read it here. It's
the reason you can biopsy the placenta during chorionic villus
sampling, or CVS, without causing bleeding."

source: http://www.jansen.com.au/silver/ch_txt04.htm ]

2. "Histiotrophic nutrition may be advantageous to the fetus during
the first trimester as it provides nutrients under a low oxygen
concentration, so reducing the risk of free radical mediated damage
during the sensitive period of organogenesis. Once this is complete,
and fetal oxygen requirements rise, there is a transition to
haemotrophic nutrition at the start of the second trimester, when the
maternal placental circulation is fully established"

http://www.ncbi.nlm.nih.gov/entrez/q...&dopt=Abstract

Any opinions welcome.