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Does A Mother’s Diet Affect Baby’s Size? 6 Things You Need To Know

You’re eating for two, have some more!

Mmm, maybe a smaller portion? You don’t want a big baby.

Your belly looks small. Have another serving. You don’t want a skinny baby!

You really shouldn’t eat that burger. How about a salad instead?

The endless advice from friends, and even strangers, can leave a mother wondering what, if any, control she really has over her baby’s size.

Does your diet affect how big or small your baby will be? Can you eat more to help your baby pack on some weight in utero? Will dieting keep your baby small, and the birth easier?

The average weight for a term infant is around 2500-3800g (5 lbs 8 oz – 8 lbs 8oz). A baby over 5000g is typically considered big. It’s important to note, however, that a ‘big’ baby doesn’t automatically mean an unhealthy baby; neither does it mean birth complications.

While your diet can affect your baby’s health, and even his size, it might not be in the way you think.

The quality, not just the quantity, of what you eat can have some impact on your baby’s size, but it can also affect his metabolism and health – even into adulthood.

Here are 6 things to know about your diet, and the effects it has on your baby’s size:

#1: There Are Many Factors Which Affect Baby’s Size

A mother’s diet certainly has the potential to affect her baby’s size. However, there are many other factors, including:

  • Genetics: the genes coming from both mother and father can determine a baby’s size
  • Pre-existing medical conditions, such as anaemia, diabetes, cardiac disease, etc
  • Maternal age: mothers over 35 are more at risk for a larger baby, probably due to medical conditions which are more common as we age, rather than just the mother’s age. Teens are more at risk for smaller babies
  • Pre-pregnancy weight: underweight mothers have increased risk of having a smaller baby, while mothers with higher BMIs are at risk for having a larger baby

#2: You Don’t Need To Eat For Two

Although you have another human being on board, you don’t need to eat as though you were eating for a second adult. Depending on build and activity level, most adults need around 1400-2200 calories per day.

Overall, you need an average of just 300 extra calories per day during pregnancy, which is approximately a medium avocado.

However, your needs vary according to the different stages of pregnancy:

  • During the first trimester you don’t really need to increase your caloric intake much, if at all. However, it’s the perfect time to make good nutritional choices
  • During the second trimester you need about 300-350 extra calories per day
  • During the third trimester you need about 450-500 additional calories per day

While it might sound like a lot, taking in 300-500 extra calories can be achieved quite easily. It’s important to eat to your hunger during pregnancy, but making healthy food choices means you eat enough to satiate, while not consuming too many calories.

Eating enough protein for breakfast can help you feel fuller, for longer. See our article, which contains 13 healthy and filling breakfast ideas. What foods you start your day with will regulate your blood sugar levels for the day.

#3: Uncontrolled Blood Sugars Can Increase Baby’s Weight

If you have Type 1 diabetes you’re at increased risk of having a larger baby. However, working closely with your endocrinologist and, if necessary, your maternal fetal medicine doctor, will help ensure both you and baby remain healthy throughout your pregnancy.

Gestational diabetes (GD) and Type 2 diabetes are often managed quite well with diet and lifestyle. If you maintain good glucose levels, your risk of a large baby is greatly reduced. The risk of a larger baby from gestational or Type 2 diabetes is typically associated with high blood sugar levels.

If you begin pregnancy at a healthy BMI, remain active, and eat a healthy whole foods diet, your risk of developing gestational diabetes is reduced. In fact, one study found a healthy diet and exercise reduced the risk of developing GD by 83%.

If you make healthy choices during pregnancy, with or without a GD diagnosis, the risk of a larger baby, as a result of uncontrolled sugar, is greatly reduced.

If you use the mindset of eating for two, and see pregnancy as the opportunity to eat whatever you desire, you might negatively affect your baby’s health and size.

#4: Intrauterine Growth Restriction (IUGR) And Small For Gestational Age (SGA) Aren’t Usually Diet Related

If you have received a diagnosis, or you’re being monitored for IUGR, you might assume eating higher calorie foods could increase your baby’s weight. Although being undernourished, or underweight, can occasionally lead to a low birth weight, typically IUGR is the result of other complications.

If you’re underweight prior to pregnancy, it’s recommended that you gain 12.5-18 kg (28-40 lbs) as opposed to the 11.5-13.5 kg (25-30 lbs) recommended for those of average weight. Typically, regardless of mother’s weight gain, a baby will grow and develop appropriately.

There are a few situations where a mother’s diet might actually affect IUGR:

  • Uncontrolled hyperemesis gravidarum (HG), leading to chronic dehydration and malnutrition
  • An underweight mother who struggles to gain and/or absorb nutrition (perhaps due to Crohn’s flares during pregnancy)
  • A teen mother who does not have adequate nutritional intake
  • Smoking, alcohol or drug use
  • Unmanaged eating disorders

Most cases of IUGR aren’t related to maternal diet. A chromosomal issue, blood clotting disorders, placental complications (previa, accreta, etc), and umbilical abnormalities are more common causes of IUGR, and aren’t affected by maternal diet.

If your maternity care provider believes your diet might be having a negative impact on your baby’s growth, it’s still important to make healthy choices. Extra carbohydrates, and highly processed, high calorie foods can help a mother to gain weight, but they lack the nutrients vital for fetal development and maternal health.

If you have been advised to increase your caloric intake, some healthy options are:

  • Nuts and nut butters (without added sugar)
  • Avocados
  • Fish
  • Healthy oils, such as olive and coconut
  • High protein, low processed foods

#5: Maternal Diet Affects Baby’s Health And Metabolism For Life

No pressure or offense intended. Keep in mind that birth weight – high or low – isn’t always indicative of a baby’s current or future health. Some babies are simply larger due to their genetic makeup, but still perfectly healthy; the same applies to smaller babies. At the same time, an average birth weight doesn’t automatically mean healthy, either.

Having a bigger baby typically becomes an issue when the size is related to uncontrolled blood sugar, and the baby has grown larger than nature intended. A baby of healthy weight can still experience the effects of maternal diet during his development.

One study found that a mother’s diet can affect the metabolism of not just her baby, but of the next three generations.

A poor maternal diet can actually cause changes in DNA, which affects how the metabolism functions. If you’re a healthy size and still struggle with insulin resistance, this might be the reason.

If you and your baby are a healthy size, but your diet contains a lot of highly processed carbohydrates (bread, cereals, pasta, sugars etc.), this could affect the metabolism.

Studies also show that maternal diet affects a baby’s immune system programming, which determines the overall immune function over the course of his lifetime.

A great tip when grocery shopping is to check the sugar content on the nutrition label of foods and drinks. The World Health Organization recommends 7 teapsoons a day for health benefits. One teaspoon is around 4 grams of sugar. So if you’re about to buy a yoghurt with 16 grams of sugar, that’s 4 teaspoons of sugar in one go. It’s an eye opening exercise!

#6: Maternal Weight Gain Can Affect Baby’s Size

Low weight gain isn’t such a common concern in most developed countries. Even women on low budgets have access to enough calories, especially through nutrition programs such as Women, Infants and Children (WIC), which provides nutritious food for pregnant and breastfeeding women in the US. Women suffering from HG, and struggling to gain weight, often have babies with healthy birth weights.

However, many studies show that high maternal weight gain is linked to larger babies. Women who gained more than 24 kg (53 lbs) had babies larger than those of women who gained 8-10 kg (17-22 lbs), independently of other factors.

Studies also find that higher maternal weight gain is linked not only to babies’ birth weight, but also to their future health, and obesity risk.

What Does All Of This Mean For My Baby’s Size?

A mother’s diet during pregnancy definitely affects her baby’s health and, in some situations, can determine baby’s weight. It isn’t necessary to count calories, or obsess over your scales. What’s important is to attempt to make healthy nutrition choices, and remain active. In fact, many of the best foods for you don’t have nutrition information labels on the packet, because they are unprocessed, whole foods.

If your midwife or doctor is worried about too much weight gain, gestational diabetes, or IUGR related to low maternal weight gain or malnutrition, then it’s a good idea to work with a nutritionist who is familiar with pregnancy diet needs.

Eating healthy fats and proteins, limiting processed carbohydrates, and remaining active can improve your health, and have a positive impact on your baby’s birthweight and future health.

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