Overview

Your doctor or midwife will monitor your weight as a metric of your health during pregnancy. Excessive weight gain or not gaining enough weight during pregnancy is associated with newborns’ low and high birth weights, preterm delivery, gestational diabetes, preeclampsia, cesarean birth, and postpartum hemorrhage. Your risk for these complications is lower if you gain a healthy amount of weight during your pregnancy. Learn about the guidelines for weight gain during pregnancy, how those translate in reality, and what you should be focused on to gain a healthy amount of weight during pregnancy.

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Weight as a Metric

Humans like metrics. Measurements allow us to assess current states and track changes over time. In the medical community, metrics are critical for setting policies and guidelines and monitoring progress and change over time. Weight and changes in weight can be indicators of overall health and growth. Sudden weight gain or loss can be a sign of a medical condition. Your pediatrician uses the weight of newborn babies as a metric for how well they are eating and growing. During pregnancy, your care provider uses your weight to assess your risk of complications and monitor the health of you and your baby.

Body Mass Index (BMI)

Life insurance companies first created weight tables as a metric to assess mortality risk. Defining ideal weight based on height is one way to assess overall health. Today, the most commonly used table is the body mass index. Scientists and the medical community have heavily integrated this calculation within health research and medicine. A mathematician in the 1800s created the calculation to calculate body mass index. It wasn’t until the 1970s that the term body mass index was coined. BMI calculates your weight in kilograms divided by your height in meters squared. You can use this calculator to determine your BMI.

BMI = (weight kg) / (height m2)

The four BMI classifications are:

  • Underweight BMI <18.5
  • Normal weight BMI 18.5-24.9
  • Overweight BMI 25-29.9
  • Obese BMI >30

BMI isn’t a perfect gauge of your health, and this calculation has limits. While it estimates body fat, it can over or underestimate fat if you have a muscular build or if you have lost muscle. There is evidence that using other metrics, like waist circumference, can be accurate metrics for predicting health risks. Although people have proposed several other calculations, none have been widely adopted to replace BMI.

Risks of Higher BMI

The health risks associated with being overweight are well known. They include hypertension, diabetes, heart disease, stroke, osteoarthritis, sleep apnea, breathing problems, cancer, mental illness like depression, body pain, and difficulty functioning. Worldwide, obesity has nearly tripled since 1975. According to the World Health Organization, at least 2.8 million people die each year due to being overweight or obese. In the United States, the rate of obesity has increased roughly 12% in the last two decades. As of 2018, the prevalence of obesity in the U.S. is 42.4%.

Risks of Higher BMI in Pregnancy

Just as being overweight or obese increases health risks for any individual, research shows a higher BMI can negatively affect fertility. There is significant evidence showing higher BMIs can increase risks for many adverse outcomes in pregnancy. This includes miscarriage, stillbirth, preeclampsia, and gestational diabetes. Studies show higher BMIs are also associated with higher rates of cesarean section. There are also documented increased risks to babies born to mothers with higher BMIs, including birth defects, macrosomia (large baby), and impaired growth.

A large body of evidence demonstrates that a higher BMI increases risks to both you and your baby. For an expecting mother with a higher BMI, your doctor may label you as “high-risk,” screen you for conditions like gestational diabetes earlier, and recommend additional ultrasounds or other monitoring throughout your prenatal care.

Health is more than Weight and BMI

A myriad of factors influences your weight and BMI. Every aspect of your life impacts your weight and overall health. This includes your genetic makeup, health conditions, hormones, and daily habits like sleep, diet, and physical activity. In a perfect world, you are at a healthy weight before getting pregnant. In the real world, that is not a reality for many expecting mothers. Changing or maintaining your weight and health is a lifelong process involving every aspect of your lifestyle. Focusing on their weight is stressful for many women, and many expecting mothers have anxiety about gaining weight in pregnancy.

Weight as a Metric During Pregnancy

Care providers look at weight gain during pregnancy to ensure you are gaining a healthy amount of weight. Excessive weight gain or not gaining enough weight during pregnancy is associated with newborns’ low and high birth weights, preterm delivery, gestational diabetes, preeclampsia, cesarean birth, and postpartum hemorrhage. Your risk for these complications is lower if you gain a healthy amount of weight during your pregnancy.

The American College of Obstetricians and Gynecologists adopts their guidelines on how much weight you should gain during pregnancy from the Institute of Medicine. ACOG recommends that practitioners determine a woman’s BMI at the initial prenatal visit to counsel her on appropriate weight gain during pregnancy. If you are considered underweight, your care provider expects you to gain more. If you start overweight, you should gain less weight. Recommended ranges for singleton pregnancies:

  • Underweight (BMI <18.5) 28-40 lbs (13-18 kg)
  • Normal weight (18.5-24.9) 25-35 lbs (11-16 kg)
  • Overweight (25-29.9) 15-25 lbs (7-11 kg)
  • Obese BMI (>30) 11-20 lbs (5-9 kg)

If you are pregnant with twins or multiples, the suggested weight gain amounts are higher. Recommended ranges for pregnancy with twins or multiples:

  • Underweight (BMI <18.5) 50-62 lbs (23-28 kg)
  • Normal weight (18.5-24.9) 37-54 lbs (17-25 kg)
  • Overweight (25-29.9) 31-50 lbs (14-23 kg)
  • Obese BMI (>30) 25-42 lbs (11-19 kg)

According to ACOG, some physicians have had controversial reactions who believe that the weight gain targets are too high, especially for overweight and obese women. Concerns have also been raised that the guidelines do not differentiate degrees of obesity, especially for morbidly obese women.

The overall recommendation from ACOG is that the guidelines from the Institute of Medicine provide a basis for practice. Individualized care and clinical judgment are necessary for managing the overweight or obese woman who gains (or wishes to gain) less weight than recommended but has an appropriately growing fetus. Balancing the risks of fetal growth (in the large-for-gestational-age fetus and the small-for-gestational-age fetus), obstetric complications, and maternal weight retention is essential but will remain challenging until research provides evidence to further refine the recommendations for gestational weight gain, especially among women with high degrees of obesity.

Stepping on the Scale

It is routine for most care providers to ask you to step on a scale at the beginning of every prenatal appointment. This can give some pregnant mothers anxiety about whether they are gaining too much weight or not enough. For someone who stresses about their weight, this can be difficult. While you can expect to weigh more at each appointment, keep in mind the weight you gain when you are pregnant isn’t all just fat or weight in your belly. The following figures are estimates and averages, and every woman is different. This should give you some guidelines of where the weight you gain comes from:

  • Breasts grow 1 to 3 pounds (0.5 to 1.4 kilograms)
  • A larger uterus adds 2 pounds (0.9 kilograms)
  • The placenta at birth is about 1.5 pounds (0.7 kilograms)
  • 2 pounds (0.9 kilograms) in amniotic fluid
  • Increased blood volume adds 3 to 4 pounds (1.4 to 1.8 kilograms)
  • The increased fluid volume contributes to another 2 to 3 pounds (0.9 to 1.4 kilograms)
  • Fat stores add about 6 to 8 pounds (2.7 to 3.6 kilograms).
  • By the end of your pregnancy, your baby weighs an average of 7 or 8 pounds (3 to 3.6 kilograms).

Weight Gain by Trimester

Weight gain is not linear throughout the whole nine months of your pregnancy. Your doctor or midwife will document your weight in a chart in your medical file. In the first trimester, you should only gain a few pounds. Then, you should experience a steady, gradual weight gain throughout your pregnancy in the second and third trimesters. You can expect around one pound per week if you start underweight or at a normal weight, and half a pound a week if overweight or obese.

Weight Gain in the Real World

Even with these guidelines, most pregnant women are not gaining weight within the suggested ranges. One study that examined over 18,000 pregnancies found that just 25.8% of women gained weight within the recommended ranges, with 21.3% gaining less and 52.9% gaining above. This was across the board for all women regardless of their pre-pregnancy weight.

A meta-analysis of 36 studies including 12,434 women found that diet, physical activity, and mixed methods effectively reduced weight gain in pregnancy, possibly decreased complications in the mother, and had no effect on the baby. The reduction in weight gain was 0.7 kg or 1.5 pounds. That may be statistically significant to a scientist, but one and a half pounds is not very much. Overall, interventions of diet and lifestyle had little effect. The researchers acknowledge that the impact of lifestyle interventions in pregnancy on long-term outcomes needs evaluation.

Most research on the Institute of Medicine guidelines finds that adherence to these guidelines helps achieve better pregnancy outcomes. The challenge is adhering to the guidelines and understanding how diet, activity, and lifestyle ultimately affect your weight gain.

Your Care Provider and Diet and Exercise Education

Hopefully, your doctor or midwife is knowledgeable about diet and exercise and can help you navigate making lifestyle changes that will benefit you during your pregnancy and in your life moving forward. Unfortunately, most health professionals do not get adequate education and training in these areas.

One study found more than one-half of the physicians trained in the United States received no formal education in physical activity. According to one report that surveyed 121 medical schools in the United States, 71% do not meet the 25-hour recommendation for diet education. 36% provide less than half of that. The lack of education in diet and nutrition is not just a problem in the United States. A systematic review of 24 studies found that medical students are not receiving adequate nutrition education in countries worldwide.

Simply getting the advice to get 150 minutes of moderate-intensity aerobic activity per week is not very helpful for someone who doesn’t have a habit of being physically active. The same goes for being told to eat healthy whole foods. (I will admit to being guilty of recommending this often.) Or the advice to only increase your calories in the second trimester by 340 calories per day and 450 in the third trimester. How many people are actually counting the calories they consume every day?

Let Your Doctor or Midwife Focus on Your Weight

Now you know what the guidelines are, and you know that most women are not gaining within those guidelines, what are you supposed to do with this information? You can expect to have a conversation with your doctor or midwife about your weight and weight gain during pregnancy. Knowing whether you are within the suggested ranges of weight gain is useful. This can let you know whether you are on track or need to make modifications.

Even for medical professionals who do have adequate training in diet and exercise, how much can you cover in a prenatal appointment that lasts fifteen minutes or less? Having you step on a scale and record your weight is a much quicker and easier metric to keep track of than to have an in-depth conversation about your diet and lifestyle. Let your doctor keep track of your weight. During your pregnancy and in the long run, there are much better places you can focus your time and energy.

What You Should Focus On

Pregnancy is a perfect time to focus on your overall health. If this is new for you, now is the perfect time to start. Your body is working harder now than in any other phase of your life. You are building a human being, and your relationship with diet, exercise, and lifestyle will be one of the biggest influences on your child. Living a healthy lifestyle and building healthy habits takes time. There are many episodes of the Pregnancy Podcast that dive into diet, sleep, staying hydrated. There are specific episodes on sugar, natural and artificial sweeteners, plant-based diets. You can also find episodes on running and walking, yoga, and more episodes focused on physical activity coming soon.

If you feel like you have a long journey to live a healthier life, you can start by taking one step at a time. Educating yourself on what habits to start working on and what healthier choices you can make is a great starting place. Over time making healthier choices gets easier.

If you want to step on the scale outside of your doctor’s office, you can do that. You can also choose not to monitor your weight outside of your prenatal appointments. There are many other indications of your health and your baby’s health than the number on a scale. You can also pay attention to other relevant metrics like how you feel, how your clothes fit, and your energy level. Any steps towards overall improving your health by eating well, getting activity, and prioritizing basics like sleep and hydration will positively impact your weight in the long run. It is one thing to be mindful of your weight during pregnancy. It is another to work on being healthier in the long term.

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