How does exercise affect pregnancy?
Resistance training is probably the most controversial topic within exercise and pregnancy. Many avoid it in fear of miscarriage or potential birth defects. But does the evidence stack up?
The Canadian and ACOG guidelines recommend incorporating resistance training and aerobic training activities for greater benefits. But what are these recommendations based on?
Firstly, for those who don’t exercise, the heavier you are during pregnancy, the heavier your newborn is likely to weigh. Even your body weight before pregnancy can influence your newborn’s weight. This means the heavier you are, the more likely your child is to be born overweight. This has negative health implications for your newborn, as being overweight or obese as a child increases their chance fivefold of becoming obese as an adult. This relationship, interestingly, does not seem to exist in those who exercise regularly, which means even if you are overweight, you can benefit from exercise.
However, it is not all doom and gloom! Light resistance training combined with an eight-minute, light cardiovascular warm-up and cool-down just three times per week during the second and third trimester is enough to attenuate these effects. And I’m not exaggerating when I say light – I mean arm and leg circles with some basic exercises like biceps and hamstring curls.
A study with newborns and their mothers showed resistance exercise did not affect the type of delivery at birth or the childbirth time, with no adverse effect on the baby’s overall health.
Even those who exercised regularly (2-3 sessions per week) had highly favourable birth outcomes compared to medium (1-2 sessions per week), low (0-1 session per week), and no exercise groups when mainly performing resistance training.
Don’t like lifting weights? Well, moderate aerobic exercise just three times per week throughout pregnancy is enough to reduce the rate of caesarean birth by approximately 7%. Further, very light exercise has been shown to reduce the odds of having a large newborn by 31% without increasing the risk of having a small newborn.
So it seems combining both aerobic and resistance exercise gives you the best chance of improving your and your baby’s health. This has been shown to have better birth outcomes than performing aerobic or resistance training in isolation.