Knowledge Base
Why is Pre-pregnancy BMI so important?
Not everyone should gain the same amount of weight during pregnancy. The Institute of Medicine (IOM) established guidelines based heavily on your Pre-pregnancy BMI.
- If you were underweight before getting pregnant, you need to gain more weight to build adequate fat reserves for breastfeeding and to support a healthy birth weight.
- If you were overweight or obese before getting pregnant, you already have existing energy reserves. Your weight gain target is lower to prevent complications like gestational diabetes and preeclampsia.
Where does the weight go?
It is a common misconception that weight gain is just "fat." During a healthy pregnancy, you are literally building a life-support system. An average 11 kg (25 lb) to 16 kg (35 lb) weight gain is broken down roughly as follows:
- Baby: 3.2 to 3.6 kg (7 to 8 lbs)
- Placenta: 0.7 to 1.4 kg (1.5 to 3 lbs)
- Amniotic fluid: 0.9 to 1.4 kg (2 to 3 lbs)
- Increased blood volume: 1.4 to 1.8 kg (3 to 4 lbs)
- Increased fluid volume: 0.9 to 1.4 kg (2 to 3 lbs)
- Larger breasts: 0.5 to 1.4 kg (1 to 3 lbs)
- Larger uterus: 0.9 kg (2 lbs)
- Maternal fat stores (for breastfeeding): 2.7 to 3.6 kg (6 to 8 lbs)
What if I am off track?
Do not panic if you are slightly above or below the trajectory curve for a week or two. Weight gain during pregnancy is rarely a perfectly straight line—it happens in spurts. However, if you are consistently tracking significantly above or below the shaded ideal zone, you should discuss your diet and activity level with your OB/GYN or midwife.