Pregnancy Weight Gain: Week by Week Breakdown

Created by Łucja Zaborowska, MD, PhD candidate
Reviewed by Rijk de Wet
Last updated: Jan 19, 2022

What's the average pregnancy weight gain week by week? Where do all the extra pounds go? Keep on reading to find all the answers!

💡 This article is a part of a bigger series, based on our pregnancy weight gain calculator.

How much weight should I gain?

Your pre-pregnancy body mass index (BMI) determines the amount of weight you should gain during pregnancy. BMI is the simplest way to assess somebody's weight and figure and compare it to the general population. However, one thing might be tricky — BMI and its implications does not apply to pregnant women! That's why we usually record the woman's weight before pregnancy and then monitor its growth rate throughout every week of pregnancy.

Remember, the formula for BMI is:

BMI=weight [kg](height [m])2\text{BMI} = \frac{ \text{weight [kg]} }{ (\text{height [m]})^2 }

Your recommended weight gain depends on your pre-pregnancy BMI:

  • Underweight before pregnancy (BMI <18.5)
    • Expected weight gain: 28–40 pounds (12.7–18.1 kg)
  • Normal weight (BMI 18.5–24.9)
    • Single pregnancy expected weight gain 25 to 35 pounds (11.3–15.9 kg)
    • Twin pregnancy expected weight gain: 37–54 pounds (16.8–24.5 kg)
  • Overweight (BMI between 25 and 29.9)
    • Single pregnancy expected weight gain: 15–25 pounds (6.8–11.3 kg)
    • Twin pregnancy expected weight gain: 14–50 pounds (16.8–22.7 kg)
  • Obese (BMI over 30)
    • Single pregnancy expected weight gain: 11–20 pounds (5–9 kg)
    • Twin pregnancy expected weight gain: 25–42 pounds (11.3–19 kg)

Eating for two: Where does all the extra weight go?

First things firsts: eating for two might not be such a good idea. Your diet should increase by only 300 kcal, starting at the beginning of the second trimester, and grow up to 500 kcal when you begin breastfeeding. 🍼

As you can imagine, all the weight gain during pregnancy must serve a specific purpose. You're not wrong: all that mass goes into the birth weight of the baby, and also allows the gestation to thrive and survive. In a typical healthy pregnancy, an average woman needs to gain around 25–35 pounds (11.3–15.9 kg).

Let's break it down pound by pound!

  • The baby: An average child's birth weight is 7.7 lb (3.5 kg).
  • An enlarged uterus weighs around 2 lb (0.9 kg).
  • Enlarged breasts weigh around 2 lb (0.9 kg).
  • The placenta adds another 1.5 lb (0.7 kg).
  • Amniotic fluid is responsible for an additional 2 lb (0.9 kg).
  • Your blood volume (increased by ~50%) and other bodily fluids: 6.6 lb (3 kg).
  • The extra fat tissue weighs close to 7.7 lb (3.5 kg).

Pregnancy weight gain breakdown by week

Achieving a healthy weight gain during pregnancy is not that difficult! Trust your body, exercise, and eat well. Don't get too attached to them sweets; turn to veggies and nuts instead. Keep in mind that the growth rate is different for every pregnancy. There is no single ideal way in which pregnant women gain weight - try to avoid comparing yourself to other future mums!

However, there's one specific thing that should catch your attention: an extremely rapid weight gain exceeding 0.5 kg (1.1 lb) per week. Track your weight, and contact your health care provider if you realize you're gaining pounds way too fast.

Here are the estimates of growth rates for the average singleton pregnancy. Remember: they do not have to fit your case entirely!

  • <14 weeks — your weight during the first trimester of pregnancy should not change.
  • 14–20 weeks — a steady weight gain appears for a total increase of 2.5 kg.
  • 20–30 weeks — an increase of another 5 kg.
  • 30–36 weeks — another 2.5 kg.
  • 36–40 weeks — at the end of the third trimester, you shouldn't gain weight anymore.

One available study broke it down to even finer pieces:

  • 0 to 10 weeks — 0.065 kg, 2.3 oz, or 0.14 pounds per week.
  • 10 to 20 weeks — 0.335 kg or 0.74 lb per week.
  • 20 to 30 weeks — 0.450 kg or 1 lb per week.
  • 30 to 40 weeks — 0.335 kg or 0.74 lb per week.
Łucja Zaborowska, MD, PhD candidate
Before pregnancy
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Weight during pregnancy
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