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I'm doing research for a series I'm writing. in it the main character is pregnant however goes off to fight a criminal organization who have been killing her friends and i want her appearance to show that she may not be pregnant however she fights and defends as if she is mindful of heavy impacts could cause a miscarriage

I am wondering how far into a pregnancy is it before visible signs of it is apparent and risk of physical trauma causing miscarriage increases, if there is also a point during the pregnancy where the fetus could mutate via outside interference then that would be good to know too however I can go without that information.

NOTE: I want to know this information so that even though the world in this series I'm writing is totally fictional, one can begin to question how fictional it really is when some parts are based off actual science and logic of real life.

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You should consider cutting down the largely irrelevant background for your specific application, and go directly to the biologically interesting question. Many will ignore your question simply because of the long introduction. Remeber that Stackexchange sites are not general chat forums. –  fileunderwater Oct 23 '13 at 10:55
    
@fileunderwater i'll cut it down given no other option, i included it so that people don't think this question is about trying to hide pregnancy –  Memor-X Oct 23 '13 at 21:08

2 Answers 2

Around the second trimester. That's an article from WedMD, which says quite a few things. To summarize, by the end of the first trimester:

You may be noticing some of the first physical signs of pregnancy: breasts that are sore or tingle at the slightest touch, skin that's drier or oilier than usual, and "morning sickness" -- which may or may not restrict itself to the morning hours. As many as 70% to 80% of pregnant women have it, but not feeling morning sickness doesn't mean there's anything wrong with the baby.

In the second trimester:

Most pregnant women begin to "show" during the second trimester. You likely gained less than 5 pounds during your first trimester, but now the number on the scale is edging relentlessly upward. As your second trimester proceeds, you'll gain an average of 1 to 2 pounds per week.

The exact time and rate of "showing" can vary, including whether or not this is your first pregnancy. By the third trimester, the infant is rapidly becoming more and more capable of surviving on its own.

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As far as "mutations" go, I think the term you're looking for is teratogenesis. Birth defects are most likely to form early in the pregnancy, but different toxins can have different windows. As an embryo develops, different tissues are growing and differentiating. If it is exposed to the right toxin at that time, that tissue may be damaged and not develop properly. If the tissue gets past that stage, exposure to the same toxin might have no affect at all.

Wikipedia may be a decent starting point: http://en.wikipedia.org/wiki/Teratogen

Studying birth defects is hard because it's tissue specific, toxin specific, and time specific. For some reason pregnant women just don't like to volunteer for studies on potentially dangerous chemicals.

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