I'm 10 weeks pregnant and gained a significant amount of weight in my first trimester. however, my bmi was underweight (110lb at 5.7ft) before conceiving. now my bmi is "normal". does being underweight before make my extra weight gain ok?

Pregnant weight: Absolutely. Those with a pre-pregnancy BMI under 18.5 should gain 28–40 pounds. Normal-weight women (BMI, 18.5–24.9) should aim for 25–35. Overweight women (BMI, 25–29.9) should aim for 15–25. Obese women (BMI, 30 or more) should gain only 11–20. Govern a starting BMI of 17.2 I would expect you to gain 40 pounds.

Yes, focus on health: Focus on eating healthy nutritious food, not on the scale. The topic of "gestational weight gain" is rather controversial and many nutrition experts recommend consultations with a registered dietician who has expertise in counseling pregnant women about maintaining healthy lifestyles (good healthy foods, vitamins, physical exercises, restful sleep...)