Nutrition & fitness

Pregnancy Weight Gain: What Happens If You Gain Too Much or Too Little

Pregnancy weight gain is one of the most obvious signs mothers-to-be can notice about their changing bodies. The baby contributes to some of that added weight, but women will definitely gain much more weight themselves as the different parts of the body require more nutrients to support fetal growth.

So, you should definitely eat for two, right?

NO. In fact, almost half of pregnant women gain too much weight during pregnancy, which can have adverse effects for you and your baby. On the other hand, almost a quarter of pregnant women gain too little, which is also problematic and associated with delivery and neonatal complications.

Both gaining too much weight and not gaining enough have their risks, so how do you strike the right balance?

This post will help you understand how to answer that question for yourself, covering the following topics:

  • What are the current guidelines for healthy pregnancy weight gain?
  • What are the risks of gaining too little?
  • What are the risks of gaining too much?
  • What can you do to ensure healthy weight gain?

How much is healthy pregnancy weight gain?

According to the American College of Obstetricians and Gynecologists, healthy weight gain during pregnancy depends on your pre-pregnancy BMI (or, body mass index).  Here is what they recommend for weight gain over the entirety of pregnancy as well as week-by-week weight gain:

  • Underweight (BMI < 18.5): Gain 28 — 40 lbs (about 1 lb/week)
  • Normal weight (BMI 18.5 — 24.9): Gain 25 — 35 lbs (about 1 lb/week).
  • Overweight (BMI 25 — 29): Gain 15 — 25 lbs (about 0.6 lb/week)
  • Obese (BMI > 30): Gain 11 — 20 lbs (about 0.5 lb/week)

These are not hard rules; it’s best to think of them as rough guidelines. Weight gain during pregnancy isn’t always linear with a steady week-by-week increase. In fact, according to the 2009 report by the Institute of Medicine, pregnancy weight gain typically looks more S-shaped (or, sigmoidal), with peak weight gain during the second trimester and early third trimester.

The bottom line? Knowing your BMI before or early in pregnancy should help guide your pregnancy weight gain. And it’s less important to gain exactly the same amount every week than it is to fall within the recommended range by the end of pregnancy.

What happens if I gain too much weight during pregnancy?

About 50% of women gain too much weight during pregnancy. It’s important to identify excessive gestational weight gain early because this can complicate your health as well as your baby’s, both in the short- and long-term.

For mothers, gaining too much weight during pregnancy increases risk for hypertensive disorders—which increases risk of preeclampsia—and gestational diabetes. Additionally, it increases the chances of having a large-for-gestational-age infant, which can increase the need for Caesarian delivery or more complex labor procedures. Large-for-gestational-age infants are also at higher risk for shoulder dystocia, or when the baby’s shoulder cannot pass through the birth canal and can damage the shoulder and arm nerves, further complicating the delivery.

In the long-term, this increases chances of women being overweight or obese several years after giving birth as well as childhood obesity for their infants.

What happens if I gain too little weight during pregnancy?

About 25% of pregnant women gain too little weight during pregnancy.

Women who gain too little weight are at a significantly higher risk for preterm birth. Infants are also more likely to be born small-for-gestational age, which is associated with its own set of adverse complications like hypothermia and hypoglycemia. Also, low weight gain is linked to other conditions, like intrauterine growth restriction, which in turn can increase risk for other complications, like perinatal asphyxia.

What can I do to keep a healthy pregnancy weight gain?

Balancing this information—don’t gain too much, but, don’t gain too little either—can be tricky. So, what should you do?

Weight gain is affected by a combination of your genes and lifestyle, and while you can’t do much about your genes, you CAN make sure to eat a healthy diet, take your prenatal vitamins. If you’re gaining too much, it can help to incorporate regular pregnancy workouts into your routine.

Another option to consider is weekly weighing at home. While this is not absolutely necessary, it’s helpful for women who are if you’re concerned about gaining too much or too little.  Just be aware that the recommended weekly gain is just a guideline (not a strict rule), and talk to your doctor if you’re concerned about any changes.

Lindsay Meisel

Lindsay Meisel is the Head of Content at Ava. She has over a decade of experience writing about science, technology, and health, with a focus on women's health and the menstrual cycle. Her work has been featured on The Fertility Hour, The Birth Hour, The Breakthrough Journal, and The Rumpus.

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