How Much Weight Should Pregnant Women Gain?
Kelsey McLaughlin, PhD
A woman’s body undergoes significant changes during pregnancy – one of the more visible changes is weight gain. However, there is often confusion regarding how much weight is normal to gain during pregnancy.
Keep reading to learn more about weight gain in pregnancy!
Why do women gain weight during pregnancy?
Weight gain during pregnancy represents the mother’s body changing to support the healthy development of her baby.
This change in body composition and weight is influenced by the mother’s metabolism and adaptation to pregnancy, as well as the growing placenta.
Approximately 1/3 of maternal weight gain is associated directly with the developing fetus, placenta, and amniotic fluid. The majority of weight gain is due to large increases in blood and fluids in the mother’s body, as well as increase in the breasts, uterus and fat stores.
How much weight should women gain during pregnancy?
In a healthy pregnant women with a singleton (one baby) pregnancy, there is minimal weight gain in the first trimester (approximately 2-4 lbs). The majority of the weight gain is in the second and third trimester, where women have been reported to gain approximately 0.6 kg per week. These numbers would be different with a twin or triplet pregnancy.
Recommendations are made based on a woman’s pre-pregnancy body mass index (BMI). Here is how BMI is calculated:
Health Canada makes the following recommendations for singleton pregnancies:
Although it is common to refer to pregnancy as a time to ‘eat for two’, pregnant women need only modest increases in calories with greater increases in vitamin & mineral consumption. The Society of Obstetricians and Gynaecologists of Canada (SOGC) recommends women within the normal BMI range, in the first half of pregnancy you only need to add an additional 100kcal to your diet per day. For example, 100 kcal is less than a typical granola bar in addition to your normal diet each day. For the second half of pregnancy, this requirement increases to an additional 300 kcal per day.
Women who are pregnant with multiple babies are expected to gain more weight, with increased weight from the babies and their tissues. Health Canada therefore makes the following recommendations for women pregnant with twins:
Due to a lack of data, recommendations have not yet been developed regarding weight gain for women pregnant with 3 or more babies.
Tracking the mother’s weight is a standard clinical assessment to help track the growth of the fetus. If women are not on track for normal weight gain, this may be due to medical conditions, diet or activity levels.
Factors that influence weight gain during pregnancy
Pre-pregnancy body mass index (BMI)
Genetic factors & family health history
Underlying medical conditions
Social & cultural factors
Does maternal weight impact pregnancy outcomes?
Yes - women who enter pregnancy at a healthy weight have better pregnancy outcomes for herself and the baby. In Canada, approximately 60% of women enter pregnancy within a normal BMI range. However, a significant number of Canadian women enter pregnancy with a clinically low BMI (BMI lower than 18.5) or high BMI (BMI greater than 25).
In addition, the amount of weight that women gain during pregnancy does impact pregnancy outcomes. In Canada, many women gain more than the recommended amount of weight during pregnancy.
Women who are overweight or obese before pregnancy or gain excessive weight during pregnancy are at increased risk of certain pregnancy complications such as including gestational diabetes, developing high blood pressure or pre-eclampsia in pregnancy, having a wound infection, or developing a blood clot. They are also more likely to receive interventions such as requiring an induction of labour or needing Caesarean delivery. There is also a higher risk of complications for the infant which include preterm delivery, delivering a larger for gestational age baby, fetal injury during birth and stillbirth. These risks also extend past the post-natal period, as infants who are born to mothers who are obese have higher rates of obesity in adulthood. Pregnant women are not recommended to lose weight during pregnancy, rather, are recommended to focus on gaining a healthy amount of weight during pregnancy.
Women who enter pregnancy with a low BMI or who do not gain enough weight are at increased risk of having a small or low birth weight infant or delivering prematurely.
How to maintain a healthy weight during pregnancy
Every woman and every pregnancy is different, it is important to speak to your doctor about strategies that will be helpful for your pregnancy.
These general recommendations are used to guide normal weight gain during pregnancy:
Setting a goal for weight gain in pregnancy
Eating a healthy, well balanced diet - meal planning or meeting with nutritionist may be helpful
Maintaining an active lifestyle - exercise is recommended for pregnant women, within limits
Maternal weight gain is an important part of normal pregnancy. Women who enter pregnancy with a low or high BMI, and women who gain a small or excess amount of weight during pregnancy are at increased risk of adverse pregnancy outcomes. Weight gain during pregnancy can also impact lifelong maternal health.
Every woman and every pregnancy is unique. Pregnant women should speak to their healthcare provider to ensure maternal and fetal safety. This article is meant to provide readers with current information and opinions. All medical and treatment decisions should be discussed with your healthcare provider.