It's funny that when you're pregnant everyone who is pregnant or ever has been shares their weight gain with the expecting mother. Some women I know gained a large amount of weight while others very little. One woman I know gained 65 pounds during her pregnancy, but you'd never know it now she said she lost it pretty quickly because she nursed. Another woman I know only gained 14 pounds which to me sounds like way too little, but she ended up having a perfectly healthy normal sized baby.
I've learned since being pregnant that weight gain suggestions vary based on your starting size. Women of average weight should gain between 25 and 35 pounds. Underweight women should gain 28-40 pounds. Overweight women need only gain 15-25 pounds. My doctor gave me a target weight gain of 20 pounds. I'm halfway through and I'm up 9 overall. So I guess I'm on track.
Here's how the weight breaks down:
Baby 8 pounds
Placenta 2-3 pounds
Amniotic fluid 2-3 pounds
Breast tissue 2-3 pounds
Blood supply 4 pounds
Fat stores for delivery and breastfeeding 5-9 pounds
Uterus increase 2-5 pounds
Total 25 to 35 pounds
You may be surprised, but a pregnant woman only needs to eat 300 more calories per day than her own body needs. For example I need about 1700 calories per day. I should only be taking in 2000 during pregnancy. If I'm eating more than that I could gain too much weight and there are a couple reason why that's not good. The obvious reason is because it's harder to lose the baby weight after the baby is born and the second reason is because it could actually be dangerous. If you gain too much weight you're at higher risk of c-section, gestational diabetes, back pain, leg pain, varicose veins, and high blood pressure.
Not gaining enouch weight also poses risks like early labor and low birth weight. So it is very important to gain weight gradually throughout pregnancy. In the first trimester many women lose weight because of morning sickness, but after that it should pick up. If sickness continues to interfere with weight gain talk to your doctor.