Letting the cat out of the bag - telling your company you are expecting.
This is a little musing for professional women who have invested heavily into their careers and are very concerned with how their family expansion will be received by their employer. The information is probably useful for any woman who plans to go back to work after having a baby, but the ones I know who are stress out over it are the ones who consider themselves ambitious career women. The only ones I knew who weren't nervous had unbelievably family friendly companies. Remember, if your manager or company doesn't become supportive, you will probably need to find a new company or manager since having a child is more time consuming than being pregnant with one (or more). Hopefully you are good at what you do and your company is more interested in keeping you than losing you so their response will be happiness gated by nervousness about if you will return. And if you are worried about being fired or laid off remember that if they aren't happy with your work, then the problem isn't your pregnancy and if they are happy with your work, you still have nothing to worry about. Relax - this will be okay.
Who to tell: Be smart - your manager should hear it from you and gossip spreads like wildfire. Tell your manager yourself when you are ready. And give your manager reassurance that you intend to return and won't leave the manager hanging (and if you don't intend to return, at some point your manager probably should know, but that's a sticky one).
When to tell: Up to you - but personally I suggest waiting until you are sure the pregnancy is viable - past the first trimester (12-14 weeks after the start of your last cycle).
What to know: Its worth understanding what your company's family leave/maternity leave policy is - its in the employee handbook if you have one. Some things to know that are confusing (and if you have a particularly complicated situation - talk to an employment lawyer for advice, don't trust a blog.) are how FMLA works and short-term disability insurance covereage. FMLA is the Family Medical Leave Act of 1993 and it basically says that if your company has more than 50 employees and you have a baby (naturally or adopted) or have to care for a sick family member, you are entitled to 12 weeks, not necessarily consecutive, of unpaid leave without risk that there will not be a comparable job for you to return to. Most companies will encourage you to use sick and vacation time to get compensated for some of your leave. In addition, some companies have short-term disability policies that will pay some or all of your compensation for some period of time following your delivery (this probably doesn't work for adoptions, but ask a lawyer if you are curious). In California, the standard is 6 weeks short-term disability for a natural delivery and 8 weeks for a Caesarian delivery. And if you start your leave prior to delivery (and I suggest you do - its hard to disappear for 3 months without some planning and the last few weeks are really tiring physically plus you will get no sleep after the baby comes for at least a little while) that's neither FMLA nor part of your 6-8 weeks, its pure disability. So you may be entitled to more compensation depending on your plan. After you've told your manager, have fun exploring this with your HR department.
What to expect - lots of congratulations and happiness. Once your news is out there - enjoy it. Its a magical and wonderful time and most people are happy for you and excited to share in it. Those who are unfomfortable may have suffered a loss (miscarriage or infertility) or may be generally uncomfortable with proof that people have sex (or at least you did). Water off a duck's back, I say, but do remember that you are blessed and be thankful for the blessing.
Have fun...