You are a regular (Wood) elf, and not a high (Eladrin) elf, right? My guess is the pregnancy will last roughly as long as a human pregnancy. High (Eladrin) elves might take longer, but I guess the close connection to nature regular (Wood) elves have would make the gestation shorter.
Of course, there's plenty of fluff books on Elves out there that include everything you'd ever want to know about elves, so you can always ask for a second opinion.
Yes, I am a regular wood elf. Stronger! I was thinking this was gonna be a problem. the only real saving grace I have right now, is a custom feat the DM made for us. our life force is linked. So we share the same HP, so if he is hurt or dies, than I die. However, i can stand back with my beloved crossbow and be a ranged fighter and heal the both of us while he goes in for the attack. This is going to get real interesting! though somehow fitting with our group. we have a TOTALLY absent minded mage and a fighter with multiple personalities... Male fighter( chaotic evil) female bard ( chaotic good). And lest we forget the (chaotic good) half demon that wants to be an angel!!
Since elves reach maturity at approximately the same rate as humans, it stands to reason that their gestation period is also similar. I'd say 10 months tops.
I was under the impression that Elves reached maturity around 110.
My group and I (amongst others, we have two chemists and a biochemist) have had many discussions about such things. I would say that the gestation period of the child would be around 18 months but it really depends on how fast Elves develop in you realm. If it is at the same rate as Human then the gestation period should be nine months. But if it is more like a century, then the fetus would also develop much more slowly, perhaps a few years. Take half-way between the two.
In the end the only real scientific way to determine gestation period is size of the mammal. Size is directly proportional to gestation period. You could use this to argue that since Elves are about the same size, the pregnancy should be about the same length. I disagree as I think that Elves are far more complex
Also this rule of thumb applies to mammals and Elves are Fey 
Of course, this may not be a 'standard procudure' situation, because it affects the hottness of elven women. Anything that reduces the hottness of an elf uses this formula: human norm divided by 10. That's hardly more than a month.
So yeah, definitely one of those two.
I was under the impression that Elves reached maturity around 110.
Seems a little strange when their maximum age is around 250.
Anyway, relevant Compendium/PHB quote:
Under Physical Qualities: "Elves mature at about the same rate as humans,"
Thank you!
the only real saving grace I have right now, is a custom feat the DM made for us. our life force is linked. So we share the same HP, so if he is hurt or dies, than I die. However, i can stand back with my beloved crossbow and be a ranged fighter and heal the both of us while he goes in for the attack.
Ask your DM how this life force link would affect your unborn child. Maybe you can boost your pooled HP by arguing your unborn child has HP as well. Of course, if he's really evil, he might try to use that against you (IE. putting the fetus at risk).
I'm using a 604 day calendar for the setting and kinda guessed that human gestation is approximately 250 days; every pregnant women experiences that with some variation. As other posters had mentioned, the maturity of elves is different than humans. So, I shifted the gestation for half-elves--when the mother is elven--to 600 (plus or minus). If the mother were human I'd have estimated about 350 days. If the mother were half-elven I'd have estimated 450 days.
The human body would not as easily handle the added months of gestation, but the pregnancy would go more peacefully. The elven body would be under the stress of gestation for a shorter time, but would find a more difficult pregnancy.
As other posters mentioned, typically elves are very long-living. That is another element of setting choices. I generally place elven lifespans under 200 years and eladrin barely beyond that. I don't like the idea of 800-900 year old elves and eladrin. That places the age of maturity at a much younger age and helps the race to blend with humans a bit better.
So, My Elven rogue Shade married another rogue in our group. He is human. She is now pregnant!! ( thanks to an evil DM..lol) How long is she supposed to be pregnant for?
At least 200 years. Then she splits down the middle, like a bacteria.
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I don't think you have to worry.
In Dragon #279's "Leaf & Thorn: The Secret Life of Elves" article, in third edition, elves are stated to carry their children for twelve lunar cycles before giving birth.
In fourth edition, no official word has been given, but given that Elves mature at the same rate as humans (full adulthood by about 20) and live to be 200, they presumably carry for nine months. They may just only become fertile once per year (instead of the human once per month).
Thank you to everyone for your help and discussions on this matter. The DM decided that our group was going to take 5 years off from adventuring we needed to create our lives and what we did during those 5 years. Shade has given birth. Thanks to some interesting dice rolls, we had half-elf fraternal twins. I named our daughter and my husband Silent named our son. We now have two beautiful children named Shiloh Bloodmoon and Ezio Bloodmoon. We have sent them to life with my elven family while we adventure and will visit as often as we can.
Congratulations!