"The recommend weight gain for a woman carrying twins is 35 to 45 pounds, which is approximately 50% more than recommended for singleton pregnancies," says David M. Barrere, M.D., FACOG, an Ohio-based Ob/Gyn. "This would represent about one and a half pounds per week after the 12th week." The recommended weight gain is based on your pre-pregnancy weight - so underweight women (with a body mass index of less than 19) and overweight women (body mass index of greater than 27) would need to gain a bit more or less.

And do the other typical pregnancy measurements still apply when you're carrying two babies? Dr. Barrere says there is no set pattern of growth that the uterus should follow. "Fundal height for twins and other multiples is useful only in showing an interval growth; but compared to singleton pregnancies, it shows an exponential growth."