The same is true for how much weight you need to gain to support your growing baby.
“There are some recommended ‘targets’ … but these are for women overall. There are always individual circumstances that can come into play,” said Dr. Kaberi Dasgupta, professor of medicine at McGill University in Montreal.
“The most important factor is that your baby is growing normally.”
However, it’s true that during pregnancy, you could need to gain extra weight in order to sustain both your life and that of the baby.
It’s also possible to gain too much weight, which can be associated with other risks.
“If you don’t carry enough weight to begin with, you need to gain more … but no matter what, you still need to eat enough protein, vitamins and minerals so your baby and body have the building blocks needed.”
Recommended weight gain targets
When you’re pregnant, you will naturally gain weight as the baby grows.
“It’s the fluid around the baby — the amniotic fluid volume — and also each woman has about an extra litre of fluid running in their blood vessels,” said Dr. Jillian Coolen, maternal fetal medicine specialist at the IWK Health Centre in Halifax.
“About 35 per cent [of an expectant mother’s weight gain] comes from the placenta.”
There are some general weight gain guidelines recommended by the U.S. Institute of Medicine (IOM) in 2009 and approved by Health Canada.
According to the IOM, what is considered a “healthy” amount of weight gain will be based on your pre-pregnancy weight and body mass index (BMI).
Your BMI is calculated by taking your weight in kilograms divided by the square of your height in metres.
Once you know your BMI, you can find your range of total weight gain as recommended by the IOM and Health Canada:
- For a BMI less than 18.5: 28 to 40 pounds
- For a BMI between 18.5 and 24.9: 25 to 35 pounds
- For a BMI between 25 and 29.9: 15 to 23 pounds
- For a BMI greater than 30: 11 to 20 pounds
“It’s important to remember that you will need to gain more weight if you have twins, triplets more,” said Dasgupta.
This doesn’t mean you should gain all the weight at once, according to Rebecca Krukowski, an associate professor in the department of preventative medicine at the University of Tennessee.
“It’s recommended that women remain ‘weight stable’ in the first trimester,” she said.
It’s also important to note that this doesn’t mean women who gain more or less than the recommended amount of weight will have an unhealthy pregnancy or birth, according to Health Canada.
Many other factors, including smoking, maternal age and underlying illness, can affect pregnancy outcomes.
To learn more, use the Health Canada calculator to determine both your pre-pregnancy BMI and your recommended weight gain amount.
The risks associated with gaining ‘too much’ or ‘not enough’
The risks associated with gaining too much weight are “well-documented,” said Coolen.
Possible outcomes include giving birth to a “large for gestational age” infant, gestational diabetes and hypertensive disorders, such as preeclampsia. You’re also at an increased risk of postpartum weight retention, which can have implications for future pregnancies and your life in general.
It can also increase your risk of high blood pressure, which can lead to early delivery and other conditions for the mom.
“Both gestational diabetes and blood pressure have an increased risk of stillbirth, and with gestational diabetes, there’s an increased risk for the baby to have low blood sugar and jaundice after birth,” she said.
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There’s less known about the possible affects of not gaining enough weight during a pregnancy, said Coolen.
However, Dasgupta said there’s some evidence to suggest that gaining too little can increase your risk of having a baby “who may be too small,” as well as premature delivery.
How to stay healthy during pregnancy
If you’re worried about your weight during pregnancy, Coolen recommends meeting with a registered dietitian.
Dasgupta agrees, saying a healthy diet of mostly vegetables, fruit and protein is key to a good pregnancy.
“You’re not eating for two — you’re eating for you and a little developing baby,” she said.
“Be careful about giving into cravings for less healthy foods like sweets and chips.”
She also recommends trying to eat regularly throughout the day, instead of all at once.
“At least three meals and maybe a snack or two, rather than cramming all your food into one or two meals,” said Dasgupta.
Most physical activity is safe for expectant mothers, but you should always check with your doctor before trying anything new.
“If you’re allowed to exercise … don’t overheat. Stay hydrated. Exercise to about 70 per cent of your max heart rate.”
She also recommends avoiding “high-risk activities where trauma could happen,” like horseback riding, contact sports and scuba diving.