Weight gain in pregnancy generally starts to become noticeable after the first trimester. During the first three months, weight gain is usually minimal, around 1 to 4 pounds (0.5 to 2 kg), because morning sickness and food aversions may limit weight gain. The more significant and steady weight gain typically begins in the second trimester, with an average of about 0.5 to 1 pound (0.2 to 0.5 kg) per week depending on pre-pregnancy BMI. This steady gain continues through the third trimester as the baby grows rapidly and the body accumulates fat reserves needed for breastfeeding.
Weight Gain Timeline
- First trimester: Minimal weight gain, usually 1-4 pounds total.
- Second trimester: Weight gain increases, about 0.5 to 1 pound per week.
- Third trimester: Continued steady weight gain, sometimes 1 to 2 pounds per week in early weeks.
This pattern is consistent across different health sources, emphasizing the importance of a gradual, steady increase rather than rapid early pregnancy weight gain.
Why Weight Gain Starts Later
In early pregnancy, symptoms like nausea may reduce appetite and food intake, limiting weight gain. By the second trimester, these symptoms often improve, leading to increased appetite and nutrient intake, which supports the growing fetus and bodily changes like increased blood volume and fat storage.
Weight Gain Recommendations by BMI
- Underweight before pregnancy: tend to gain more weight overall.
- Normal weight: moderate weight gain starting slowly in the first trimester.
- Overweight or obese: slower weight gain starting after the first trimester.
Most guidelines recommend an additional 300 calories per day starting in the second trimester to support healthy weight gain and fetal growth.
In summary, weight gain starts slowly during the first trimester and accelerates in the second trimester, continuing steadily through to the end of pregnancy. The exact timing and amount vary according to individual circumstances and pre-pregnancy weight.
