I've has several pregnancies where I have gained under twenty pounds, two where I have gained 20-30, and here at my lightest weight I've gained almost 40 pounds in the first trimester as a bizarre slingshot effect to having dropped about twenty of those a few weeks before conceiving. I've run the gamut. As much as I'd like to say you can control these things, that has not been my experience. Eat nutritious food, in quantities that satisfy you without stuffing you, and screw the scale.
I've been fifteen pounds lighter at childbirth than prepregnancy, and I've had fifteen pounds to lose post baby. I haven't gone nuts in either case. But the fact remains that some pregnancies seem to require different things of my body and the lighter I get, the more I tend to gain, even eating the same whole foods diet.
Think *nutrition* when building babies, not weight. Focus on nutritionally dense food. Don't use if as an excuse to pound back pastries. Do not, under any circumstances, limit protein or fat intake. Simple enough
This is my fifth healthy baby and seventh pregnancy, if there is one thing I have learned it is how not in control I am when it comes to my body's processes and needs. Just give the sufficient raw material and let the rest take care of itself.