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How much weight should the average woman gain during pregnancy?

Updated: Jun 8

Although all weight gain throughout pregnancy is important, a fascinating study by a group of American researchers determined that maternal weight change in the first trimester of pregnancy more strongly influences newborn size than does weight in the second or third trimesters!

Weight gain during the first trimester predominantly consists of fat stores, fluid (as a result of a change of hormones) and increased blood volume.

Unless you are underweight at conception it is recommended that you don’t gain more than 2 kilograms (4.4 pounds) during the first trimester. Ideally, this weight should come from fluid stores as, even at 12 weeks, the baby is only about the size of a plum. Additional weight gain during the first trimester is usually adipose (fat) tissue.

After this, weight gain should occur at a relatively even rate of approximately 100–500 grams (0.5-1 pound) per week.

A woman of a healthy weight before conception (a BMI of 18.5–25) should aim to gain approximately 11.5–16 kilograms (25-35lbs) by the end of her pregnancy. Although every woman’s body is different, this will consist of approximately:

  • 3.5 kilograms (7.7 pounds) of baby weight

  • 1 kilogram (2.2 pounds) amniotic fluid

  • 0.5 kilogram (1 pound) of placenta

  • 1 kilogram (2.2 pounds) uterus

  • 1.5 kilograms (3.3 pounds) blood

  • 1 kilogram (2.2 pounds) fluid - The swelling is a result of hormone fluctuation, increased blood volume and the pressure of the baby on the veins around the groin slowing the movement of fluid around the body.

  • 0.5 kilogram (1 pound) breast tissue – as a result of increased estrogen levels.

  • 3 kilograms (6.6 pounds) body fat – increased estrogen levels will also encourage the body to store more body fat known as adipose tissue. This adipose tissue is important for providing additional padding to protect the foetus during pregnancy and also to ensure that the mother has plenty of stored fuel to feed the foetus in case of famine.

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