13 Pre-Pregnancy Weight And Healthy Weight Gain During Pregnancy Are Predictors of a Healthy Pregnancy
How does a pregnant woman know if her energy and nutrient intake is sufficient?
Growing a baby requires a great deal of energy and utilization of nutritional stores. While the average birth weight of a baby is about 7-8 pounds, a woman will typically gain well over that amount throughout the pregnancy due to the increased blood and fluid volume, fat reserves, breast enlargement, and the weight of the placenta and amniotic fluid.
Usually, nutrition professionals recommend that pregnant women eat a plant based, nutrient dense diet with added dairy, small portions of fatty fish, eggs, and lean meat. In short, nothing special. During the last chapter you also learned that the energy need varies widely from woman to woman depending on the physical activity level and the amount of exercise. How do women know how much to eat?
You Will Learn:
- Adequacy of nutrition during pregnancy is determined by maintaining a recommended weekly weight gain (GWG).
- Recommended weight increase depends on the pre-pregnancy BMI
- Recommended weight increase is around 1 pound per week for woman entering the pregnancy with a BMI under 25.
- Recommended weight increase is 0.6 pounds/week for overweight women and 0.5 pounds/week for all obese women.
- Today, more women enter pregnancy overweight or obese increasing the risk for pregnancy complications. Only 1/3 of pregnant women achieves recommended weight gain.
- The main pregnancy complications—GDM, hypertension, pre-eclampsia—are connected to the combination of pre-pregnancy weight and weight gain during pregnancy.
- Maternal obesity is linked to an increased risk for adverse outcomes to the fetus, birth, and child development.
- Being underweight before pregnancy combined with insufficient weight gain during pregnancy increase the risk for adverse outcomes to the fetus.
- Free prenatal care should be offered to all pregnant women. Care should include individualized attention.
Recommendations for Weight Gain in Pregnancy Vary Depending on the Pre-Pregnancy BMI
The first step at every prenatal check-up is a trip to the scale. The weight increase throughout the pregnancy is closely monitored because gaining too much or too little weight is a risk factor for pregnancy complications.
The following table depicts the current recommendation for weight gain during pregnancy. There are two important general facts embedded in those data:
- Weight gain is not expected until the second trimester (a small amount of weight gain around 0.4 pounds per week is expected during the first trimester in women with a low or normal BMI for adipose tissue growth)
- Expected weight gain depends on the pre-pregnancy BMI.
BMI stratified GWG (gestational weight gain) recommendations are relatively new. During the first part of the 20th century it was recommended that pregnant women gain up to 20 pounds during the pregnancy. This recommendation was increased to 20 – 25 pounds in the 1970s.
At the beginning of the 21st century, the increasing prevalence of obesity resulted in increasing numbers of women entering the pregnancy overweight and obese. This situation required rethinking of the weight gain recommendations. As a consequence, new GWG recommendations stratified by pre-pregnancy BMI were employed.
The primary goal of these weight gain recommendations is the reduction of pregnancy complications. Women who gain more weight than the GWG recommendations have a higher risk for pregnancy complications such as gestational diabetes, hypertension and preeclampsia. The risk also increases for macrosomia and birth complications. If the weight gain is below the recommendation the newborn tends to be and has a risk of a premature birth.
Studies researching both pre-pregnancy BMI and GWG in relationship to pregnancy outcome, have two more interesting findings:
- The pre-pregnancy BMI is a stronger predictor for negative pregnancy outcomes than the gestational weight gain.
- Excessive weight increase during the first trimester is a stronger predictor than weight increase during the second and third trimester.
The second reason, often neglected, why excess maternal weight gain should be avoided is that it is often persistent after pregnancy. Excessive pregnancy weight gain is a predictor for obesity and chronic diseases.
There is another concern—a woman going through several consecutive pregnancies and retaining additional weight after each one, will not only become obese, but go into each successive pregnancy with a higher BMI. This will increase the risk for adverse pregnancy outcomes for the consecutive pregnancies.
Studies show that Black women as well as those with low income tend to retain more weight postpartum than white and Hispanic women regardless of their pre-pregnancy weight.
To understand the idea behind those recommendations, understanding the composition of the pregnancy weight gain is important (Champion ML, 2020). The pie chart shows that at the end of the pregnancy half of the weight gain stems from the feto-placental unit (fetus, placenta, amniotic fluid, uterus). Another 25% is associated with blood volume, extracellular fluid and breast tissue.
The remaining weight gain, roughly another 25%, stems from maternal fat stores. This additional energy store for pregnancy and breastfeeding is not needed if women bring large adipose tissue stores into the pregnancy. On the opposite spectrum underweight women should gain more adipose tissue.
Therefore the recommended gestational weight gain (GWG) is lower in overweight and obese, and higher in underweight women depending on their existing adipose tissue stores. This thinking is backed by observational studies.
The recommendations can be applied to women of short stature, pregnant adolescents, and racial and ethnic minorities.
For women carrying twins different recommendations apply. The current recommendations according to BMI are the following:
- Underweight: 50 – 62 pounds
- Normal weight: 37-54 pounds
- Overweight: 31-50 pounds
- Obese: 25-42 pounds
Why Are We Using Pre-Pregnancy BMI, But Weight Gain in Pound For GWG?
One of the most common tools to measure obesity is the Body Mass Index or BMI.
This is a simple and inexpensive measurement calculated by dividing a persons weight by their height. However, BMI is not an ideal measurement to determine the risk for chronic diseases, but more easy measuring techniques to determine body fat are still missing for quick determination of body fat at a physician’s office.
The BMI works reasonably well for the majority of the American adults as a rough scanning tool to determine if a health care provider needs to follow up or if a pregnant women needs to gain more or less weight during pregnancy. We need to be aware of the population groups that BMI measurements do not work for though. This includes adults who have a high lean body mass or are very tall or very short.
Here is another group the BMI does not work for: Pregnant women. While the physician will use the BMI to scan if a woman might be in a risk group at the beginning of the pregnancy, the BMI is off the table during pregnancy. Here is why:
During pregnancy the body composition changes. This includes an increase of body water from about 50-60% to 72-74% as well as a fat mass increase of about 6-7%. Mineral and protein content go up as well. All of these factors contribute to an increase in weight and thus a difference in calculated BMI.
The main predictor for a healthy uneventful pregnancy is the combination of pre-pregnancy BMI and weight gain during pregnancy. Studies show that both parameters are correlated to the likelihood of pregnancy complications.
More Pregnant Women Enter Pregnancy Overweight And Do Not Adhere to the GWG Recommendations
Studies investigating the connection between pre-pregnancy BMI, pregnancy weight gain, and pregnancy outcome demonstrate clearly that:
- Women entering pregnancy with a BMI in the normal range have the lowest risk for pregnancy complication and negative outcomes.
- Women who gain the recommended amount of weight for their pre-pregnancy weight have the lowest risks of pregnancy complications in their BMI group.
Today, More Women Enter Pregnancy Overweight or Obese
As mentioned before due to the increasing prevalence of obesity over the last two decades more women enter pregnancy obese.
Today, almost 32% of women in the reproductive age are obese and 7% are categorized as . When combined with overweight women, the prevalence is almost 56%.
The prevalence in African-American and Hispanic women is even more worrisome. 56% of African American women in the reproductive age range are obese with 74% overall being obese or overweight.
Pregnant Women Often Do Not Meet the GWG Recommendations
Here is the concerning reality. Statistics show that almost half of pregnant American women gain weight above the GWG recommendations. Only a third of pregnant women manage to stay within the recommendations.
When we look at the development of GWG over the last decades something else becomes clear. Extreme weight gains, either above or below the recommendation range, become more and more common.
The graph below shows that both excess weight gain over 40 pounds has become more common as well as low weight gain.
A concern we haven’t talked about are women that diet during pregnancy. When the GWG recommendations were developed the scientist also considered if weight loss during pregnancy would help obese mothers reduce their risk for LGA newborns, macrosomia, and cesarean. The risk was reduced, but the risk to give birth to an SGA infants increased. In addition, the risk for pregnancy complications was not reduced.
The second consideration is that high blood concentrations of ketones, potentially occurring during weight loss, seem to have a negative impact on neurological development of the fetus.
The conclusion was that weight loss during pregnancy is not recommended.
The Main Pregnancy Complications—GDM, Hypertension, Preeclampsia—Are Connected to High Pre-Pregnancy BMI And Excessive Weight Gain During Pregnancy
During the last century maternal mortality decreased substantially in high income countries. Reasons for this improvement are many advances in medical care, such as blood transfusion, antisepsis, improved operative and anesthesia techniques and antibiotic use.
While other affluent countries kept lowering their maternal mortality rates the US rates are disturbing. The US has by far the highest maternal mortality rate of all developed nations with 26 out of 10,000 pregnancies. The next highest is the United Kingdom with slightly over 9 out of 10,000 pregnancies.
Not only does the US have an astoundingly high maternal mortality rate, but while most other developed countries keep lowering their maternal mortality rates, the US rate has gone up steeply.
Also, there are disparities in maternal mortality affecting African–American women more than Caucasian women.
Causes are not fully clear, but increasing maternal age combined with the high percentage of overweight and obese pregnant women and the lack of prenatal health care for low-income women are discussed.
While many obese women have normal pregnancies and healthy babies, from a public health standpoint the increased risk for maternal death makes it important to learn about consequences of obesity for pregnant women.
Gestational Diabetes (GDM)
According to the CDC 2-10% of pregnancies in the US are affected by gestational diabetes every year. 50% of women developing GDM go on to develop T2D. Even more concerning is that we saw a steady increase in GDM starting 1990 when the prevalence was 2%. By 2004 this number doubled.
2 or 4% of pregnancies does not sound like that much, but if you multiply this percentage with roughly 4 million life births that take place every year in the US you will have 92,000 women developing GDM each year. From a public health standpoint this is a concerning number.
Before you learn about the connection between obesity and GDM it is important to keep in mind that GDM is not solely an obesity related pregnancy complication. Genetic predisposition for insulin resistance can result in GDM during the last trimester of the pregnancy in otherwise healthy, lean women. Obesity is aggravating the genetic predisposition.
Here is the problem. Many obese women already bring insulin resistance into the pregnancy even if they are at this point not diagnosed with prediabetes or T2D.
You are already familiar with physiological insulin resistance during pregnancy. The following infographic depicts how pathological insulin resistance aggravates the physiological insulin resistance during pregnancy:
Starting during the second trimester, muscle and adipose tissue are becoming progressively less insulin sensitive. Blood glucose concentrations after a meal stay longer elevated and insulin secretion increases to compensate for the elevated blood glucose levels.
In obese women, the insulin sensitivity is already lower and insulin levels are higher after a meal before the woman even reaches the second trimester.
By adding the physiological adaptions on top of the existing insulin resistance and elevated insulin blood levels, this might strain the pancreas enough that insulin secretion and glucose tolerance decline.
GDM or excessive insulin resistance tend not to have clearly noticeable symptoms. Therefore, a routine glucose tolerance test between week 24 and 28 evaluates how fast glucose is cleared after a meal. The pregnant woman drinks 8 ounces of a 100 g sugar solution. The blood glucose is measured after 1 hour. If the blood glucose concentrations are 180 mg/dl or higher blood is taken at the 2 hour and 3 hour mark. A diagnosis of GDM is made when 2 or more of the blood glucose levels meet or exceed a threshold.
GDM is associated with increased blood glucose concentrations, delayed clearance after a meal, and the release of more free fatty acids from the adipose tissue. The consequences are similar to T2D. An overworked pancreas, cytotoxic glucose, and free fatty acids can damage the beta cells of the already strained pancreas.
Once the pancreas is not able to compensate for the insulin resistance by increasing insulin secretion, blood glucose levels will be elevated for much longer after a meal. The mother will consequently be diagnosed with gestational diabetes.
Here is an interesting study that demonstrated the additive effect of reduced insulin sensitivity before pregnancy due to obesity and physiological insulin sensitivity during pregnancy:
Obese and lean women enter the pregnancy with different levels of insulin sensitivity. This difference remains stable throughout the first trimester. Insulin sensitivity declines for both lean and obese women during second and third trimester but the decline is much more pronounced for obese women and can reach the point when the woman develops GDM.
Normal weight women return to a normal metabolism within a couple of weeks after birth. In obese women, the damage to the pancreas due to the cytotoxic effect of glucose and free fatty acids combined with the strain of high insulin production can be enough to lead to aT2D diagnosis after pregnancy.
GDM is also a risk factor for developing T2D later in life.
There are some ways to reduce the risk of experiencing gestational diabetes. Some studies show that increasing physical activity as well as consuming a Mediterranean or DASH based diet reduces the risk.
Preeclampsia And Hypertension
One of the worst case scenarios in pregnancy is preeclampsia, a truly scary condition, that can lead to premature birth, stroke and potential death of the mother and fetus. Maternal age, obesity, and the lack of pre-natal care contribute to the risk of developing preeclampsia.
Again 3 % of pregnancy might not sound like a lot, but from a public health stand point this translates into 80,000 women affected by preeclampsia each year.
Recall from the pregnancy preparation chapter that preeclampsia has a variety of symptoms that tend to show up during the last half of the pregnancy. What makes this disease even more worrisome is that it can happen after a seemingly normal birth with no symptoms. It becomes especially dangerous because many women, and even health care providers, dismiss one of the more common symptoms, the sudden severe headaches.
If preeclampsia develops during the pregnancy the best outcome is a prematurely born baby since delivery is the only treatment to treat and reverse preeclampsia. Depending how early the baby is born it will face many obstacles during the first months of life and run the risk of permanent disability.
The best way to prevent preeclampsia is to start the pregnancy as metabolically healthy as possible. During the pregnancy blood pressure and protein content in the urine should be consistently monitored at regular prenatal visits since those are the first two symptoms of a developing preeclampsia.
Maternal Obesity Is Linked to Fetal Risks
Fetal Risks During Pregnancy, Birth, and Child Development
Obesity during pregnancy increases not only risk for the mother, but also for the fetus during pregnancy and birth. Preterm birth, very small or large birthweight can even affect metabolic health throughout the lifetime of a child.
The risks to fetal health also stem from the obesity induced exaggeration of the normal physiological adaptations during pregnancy.
You might think, why does it matter if a baby is larger at birth? Large babies can get injured during their passage through the birth canal. If the infant is too large to be born naturally, a C-section will be necessary. C-sections are risky for obese mothers for a variety of reasons. Anesthesia has increased risks in obese women and epidurals are sometimes hard to place. Slow wound healing and infection of the incision is also a risk for obese women.
Aside from the maternal risks, a newborn with macrosomia will have an altered body composition and higher fat percentage. Newborns with macrosomia are more likely to become obese throughout life.
In addition the large newborn needs emergency attention after birth. The baby will be born with low blood glucose levels and have trouble regulating their blood glucose levels. is also likely and needs to be treated. Hyperbilirubinemia, commonly known as jaundice, is common in many newborns but very common in LGA babies. Severe cases are treated with UV light.
Large for gestational age (LGA) babies seem to have more cardio-metabolic issues later in life. It is hard to determine if this is due to epigenetic programming because parents were obese, the metabolically unfavorable conditions during pregnancy (which can also cause epigenetic changes), or the lifestyle after birth. Studies show that part of the problem can be explained by a .
While the maternal mortality in the US is trending upward, we made incredible strides lowering the infant mortality rate. Thanks to technology some premature babies are now able to survive after being born as early as 22 weeks. (Interested? See the Nature article).
Despite all those improvements, obesity increases the risk for for miscarriage, premature birth, or stillbirth birth due to a placenta that is not functioning optimally and maternal pregnancy complications. While technology is advanced, the risk for permanent medical issues is still high the earlier the baby is born.
Additionally, obesity during pregnancy increases the risk for an array of congenital abnormality.
Underweight Pregnancies Bring Increased Risk
While obesity increases risks for mother and fetus, going underweight into the pregnancy will mostly affect the fetus.
Here is the good news. While a high BMI at conception is the main risk factor for pregnancy complication even if the weight gain follows the recommended GWG, underweight women at conception who gain sufficient weight during the pregnancy will most likely give birth to a healthy baby.
If the underweight pregnant woman does not gain sufficient weight the infant has the risk of preterm deliveries, SGA, and increased risk of neonatal mortality. Studies following small for gestational age (SGA) babies show that many develop a and are more likely to be obese later in life.
One at risk group going into a pregnancy underweight are adolescents.
The United States takes the trophy again for having the highest teen pregnancies (59 for every 1000 women) out of 21 different industrialized countries according to a study conducted in 2015.
Digging further into the research, disparities can be found among Hispanic and Black populations that, together, accounted for over half of the teen pregnancies in 2017. However, there has been a decline in recent years which is associated with teens practicing safer sex or who are sexually active while on birth control.
For those that end up becoming pregnant, there is an added component to being underweight. Adolescent girls can still be in a rapid growth phase and will end up needing energy and nutrients for their metabolism, growth, and the pregnancy.
American teenage women tend to have lower nutrient stores and nutrient intake across the board and nutrient deficiencies seen in folate, iron, and calcium. Insufficient energy intake during pregnancy leading to low weight gain will prevent the placenta and fetus from growing sufficiently. The consequence is a newborn that is small for gestational age (SGA baby).
The most complications (especially SGA babies) are seen amongst the 12-15 year old pregnancies where the adolescent is still rapidly growing and further has to compete for nutrient intake.
The teen’s pregnancy occurrence or success may be linked to her prenatal weight, socioeconomic status, education level, and access to prenatal care. Regardless of the situation, one of the most important factors is ensuring that the mother can maintain a healthy weight while increasing her nutrient intake substantially in order to provide for the growing fetus.
Personalized Nutrition Care Should be Provided During the Pregnancy and After Birth
The best strategy to reduce the risk for pregnancy complications is a healthy, plant-based, mixed eating pattern combined with sufficient amounts of physical activity and moderate exercise. In reality, only 1 % of pregnant women eat the recommended amount of fruits and vegetables. Whole grain and legume intake is also lacking. Instead, women have a high intake of solid fats and sugar, and only 25 % of pregnant women have sufficient exercise.
Obstetricians are rarely not educated to address weight or a healthy lifestyle. In order for a woman to reduce the risk of weight complications during pregnancy, it would be ideal if prenatal care is offered to all pregnant women and that this care would include personal nutrition counseling and exercise recommendations.
Important concepts to discuss with the woman would be an optimal GWG throughout pregnancy and how to achieve it. This would include personalized nutrition, physical activity counseling, and post-pregnancy plan to return to normal weight appropriately.
Interested in More Information?
https://www.cdc.gov/reproductivehealth/maternalinfanthealth/pregnancy-weight-gain.htmDance A. Survival of the littlest: the long-term impacts of being born extremely early. Nature. 2020;582(7810):20-23. doi:10.1038/d41586-020-01517-z
Editors: Sydney Christenson, Eric Hanzel, Gabi Ziegler
- Spring 2020: Julia Curtis, Colleen Sherman, Kendyl Heuertz, Gage Gauchat, Miranda Haverdink, Amelia Johnson, Maddie Korthas, Krissy Krager
- Fall 2020: Morgan McCain, Pierce Krouse, Miles Judson, Peyton Hainline, Megan Appelt
Small for gestational age
BMI > 40
Low blood magnesium concentrations
Energy efficient metabolism that requires fewer calories for daily activities