When are you due?
Never, under no uncertain terms, ask a woman if she's expecting -- not even if she's in the maternity ward being wheeled off to give birth. (Okay, maybe then... maybe.) Women come in all shapes and sizes and it might look to you like someone is pregnant, but that might not be the case. You don't want to get caught in an embarrassing situation where the woman tells you she doesn't have a bun in the oven. How will you pull your foot out of your mouth?
Are you having twins?
In many cases, a pregnant woman is not having twins. And for that matter, the woman you're asking may not even be pregnant (see number one). Pregnant women carry their baby weight differently. Women who are expecting also become swollen, especially toward the end of their third trimester. So if you're engaged in a conversation with a woman and already know she's pregnant (because she told you, you didn't ask), let her be the one to offer the information that she has not one, but two buns in the oven. Because there's nothing worse than making a pregnant woman feel self-conscious about her size.
Did you go through fertility treatments?
If a pregnant woman tells you that she's expecting multiples (remember, you didn't ask her, she offered... see number two), don't follow up with a question asking if she sought fertility treatments. Maybe she did, maybe she didn't. Either way, that is a personal matter and may not be something she's prepared to discuss.
Do you plan to breastfeed?
Unless you are talking to your best friend, your sister or yourself, this is also a very personal question that should not be asked. Oftentimes, a woman is still trying to make many important decisions about her baby while she's still pregnant. The choice to breastfeed or bottle feed is not always easy for a woman. So follow the rule of thumb that if she wants to talk to you about nursing, she will. If it doesn't come up, don't be the one to bring it up.
Why did you choose that name?
You've been chatting with a pregnant woman and she tells you the name she's planning for her baby. Don't question the name she's picked (unless she asked you for your opinion... but even then, tread carefully). If it's not your favorite name in the world, just smile and change the subject.