What Is Gestational Weight Gain?
Normal physiologic and metabolic changes occur during pregnancy and are related to variable growth rates of maternal, placental, and fetal components that contribute to increased gestational weight gain (GWG), or weight gain from conception to delivery. Usually, pre-gravid weight is self-reported. As pregnancy progresses, the accumulation of FM, FFM (i.e., protein accretion), TBW, and minerals is deposited in the fetus, placenta, and amniotic fluid, which contribute to the fetal component of GWG or ~35% of total GWG [39]. Conversely, the developing uterus and breast tissue, as well as extracellular fluid, blood, and adipose tissues, contribute to the maternal component, or ~65% of total GWG [39].
The recent Institute of Medicine Report on the 2009 Guidelines for Recommended Weight Gain during Pregnancy defined recommendations for total weight gain in pregnant women according to the different classes of pre-gravid BMI, as shown in Table 4. While the first trimester is usually characterized by only a slight total weight gain of approximately 1–4 lbs. (or 0.5–2.0 kg), the second and third trimes- ters feature the predominance of the weight gain during gestation. Figure 1 show- cases early and late GWG contributions to maternal and fetal units. Gestational weight gain is inversely related to pre-gravid BMI. For example, women with nor- mal to underweight pre-gravid BMI are recommended to gain weight at a rate of approximately 1 lb. (~0.4–0.5 kg) per week during the second and third trimesters, with overweight women recommended to gain 0.6 lbs. (~0.3 kg) per week, and obese women 0.5 lbs. (~0.2 kg) per week [40]. The current guidelines state that women with GWG that exceeds these recommended ranges are more likely to retain weight postpartum and are at increased risk for subsequent obesity. Indeed, abnor- mal or excessive GWG is a strong predictor of pregnancy outcomes for both women and infants. For example, the odds of developing abnormal glucose tolerance in the third trimester of pregnancy are greater with higher rates of GWG [41]. Maternal obesity and weight retention postpartum are also associated with excessive GWG [42]. In addition to these maternal outcomes, excessive GWG is associated with infants born large for gestational age, and excessive neonatal and infant weight [43–45].
What Causes GWG?
GWG can be brought about by a variety of factors. The physiological alterations discussed later in this chapter are some of the contributing factors, but others include age, race, and pre-gravid BMI. Increased maternal age has been found to be associ- ated with an increased risk for low birth weight and small-for-gestational-age chil- dren [46, 47]. Furthermore, Gross and colleagues found that obese women ≥35 years
Table 4 Recommended total weight gain ranges by pre-gravid BMI during pregnancy
Pre-gravid BMI BMI (kg/m2)
Total weight gain range (lbs)
Rate of weight gaina during second and third trimester [Mean Range in lbs/week]
Underweight <18.5 28–40 1
[1.0–1.3]
Normal weight 18.5–24.9 25–35 1
[0.8–1.0]
Overweight 25.0–29.9 15–25 0.6
[0.5–0.7]
Obese (includes all
classes) ≥30.0 11–20 0.5
[0.4–0.6]
aCalculations assume a 1- to 4- lb. (or 0.5–2.0 kg) weight gain during first trimester
Fig. 1 Components of gestational weight gain (GWG) since last menstrual period. Maternal and fetal components of GWG are noted. Panel (a) represents Early GWG (0–<24 weeks) and Panel (b) represents the Total GWG (0–40 weeks). Late GWG contributions are simply the difference between Total and Early GWG. The stated contributions to GWG are from those of a healthy BMI woman who gains within the recommended IOM weight gain guidelines throughout pregnancy.
Women who gain above the recommended guidelines are expected to contribute larger GWG in both the maternal and fetal units. (Percentages adapted from Pitkin RM. Nutritional support in obstetrics and gynecology. Clin Obstet Gynecol. 1976 Sep;19(3):489–513)
old had inadequate GWG compared to younger women (25–29 years) [48]. How these factors and differences among obesity classes affect birth outcomes has yet to be elucidated. Race is another factor that influences GWG; a large epidemiology study of approximately 53,000 women found that black women were significantly more likely than white women to gain less than 15 lbs., but less likely than white women to gain greater than 34 pounds [49]. Further, the IOM noted a study of 913,320 women between the years 1995 and 2003. Asian and non-Hispanic black women were more likely to gain 0–9 kg while Hispanic and non-Hispanic white women were more apt to gain more than 20 kg during pregnancy [40]. Larger epi- demiological studies that control for health disparities are warranted, specifically comparing differences in GWG across races.
Recent increases in maternal pre-pregnancy BMI has brought to light a number of studies showing that maternal pregnancy outcomes are worsened with increasing degrees of maternal BMI at conception [50, 51]. Generally, GWG is inversely pro- portional to maternal BMI status [49] The authors found that obese women tended to gain less weight than normal weight or overweight women; however, a quarter of the obese women still gained greater than 35 pounds. As detailed earlier, women who gain weight above the normal recommended IOM Guideline’s weight gain ranges during pregnancy are at increased risk of experiencing adverse maternal out- comes prenatally, at delivery, and postpartum.
Implications of GWG on Maternal Physiology and Outcomes
During Pregnancy
Among the well-studied adverse prenatal maternal outcomes that result from exces- sive GWG are gestational diabetes mellitus (GDM) and impaired glucose tolerance, as well as pregnancy-associated hypertension (including preeclampsia and eclamp- sia). Although pregnancy is frequently accompanied by a pronounced physiological decrease in peripheral insulin sensitivity, the combination of decreased peripheral insulin sensitivity and beta-cell dysfunction can lead to the development of abnor- mal glucose tolerance during pregnancy, or GDM. Indeed, women who enter preg- nancy as obese, as well as women whose GWG is above the ranges recommended by the IOM Guidelines, tend to develop more pronounced insulin resistance and abnormal glucose tolerance and are at greater risk for GDM than are non-obese women [52–56]. Some studies even report that women whose GWG was below the recommended range had a higher likelihood of GDM [56–58]. However, there have been studies finding no significant association between GWG and glucose tolerance [59–61].
Weight gain above recommended ranges might also increase risk of experiencing pregnancy-associated hypertension. While the association between GWG and hypertensive conditions remains unclear due to limited and inconclusive data [54, 57, 58, 62, 63], some studies (all rated fair or poor in quality) have reported such
an association does exist [58, 63], with others lack consistent control for confounding.
Interestingly, the timing of GWG may influence different physiological and met- abolic factors throughout pregnancy. Specifically, GWG above the recommended guidelines in the first trimester has been shown to be predictive of excessive GWG for the entire pregnancy [64]. Women with a normal-weight preconception BMI have a 70% probability of excess total GWG when excess weight gain is experi- enced in the first trimester, while overweight and obese women have a 90% proba- bility of excess total GWG [65]. While research is limited, excess GWG, independent of total GWG, has been shown to be associated with impaired maternal glucose tolerance later in pregnancy [66] and greater infant adiposity at birth [65], therefore making future adherence to the recommended weight gain guidelines possibly more critical in these early stages of pregnancy.
At Delivery
Excess GWG has also been suggested to increase the risk of complications during labor and delivery, as well as increased likelihood of cesarean section. The evidence for an association between GWG and cesarean delivery is inconsistent, however, in part because of failure in some studies to adjust for route of prior delivery among multiparous women [67]. Moreover, moderate evidence exists on the association between excess GWG and cesarean section over the last decade [63, 68–73], while several recent studies failed to find an association [57, 60, 74]. Additionally, pre- gravid obesity by BMI categorization has been shown to place women at higher risk of cesarean delivery [60, 70–72, 74].
Postpartum
In the postpartum period, potential consequences of excess GWG during pregnancy include weight retention, decreased lactation performance, and postpartum depres- sion, likely as a consequence of weight retention.
Higher GWG is associated with greater postpartum weight retention, yet many studies fail to consistently adjust for dietary intake, physical activity, and breast- feeding behavior [67]. Nonetheless, subsequent postpartum weight retention increases the risk of moving into a higher BMI category regardless of subsequent pregnancies, thereby increasing the risks to the woman and her fetus during subse- quent pregnancy, and to the woman’s own longer-term health and risk of cardiovas- cular disease, type 2 diabetes, cancer, and mental health.
While data is inconclusive, unsuccessful lactation, or decreased lactation perfor- mance, may also result from excess GWG during pregnancy. One study has exam- ined the relationship between GWG and lactation and did not find any relationship between GWG and either milk quality or quantity [75]. While obese women have been reported to have shorter breastfeeding duration regardless of GWG [76–79],
the evidence for any association between GWG and duration of exclusive or any breastfeeding was rated weak; evidence that low weight gain is associated with decreased initiation of breastfeeding was rated moderate.
Implications of GWG on Infant Physiology and Outcomes
Excess GWG
Historical examinations of weight gain in pregnancy conclude that very little weight gain occurs in the first trimester and weight thereafter increases linearly until deliv- ery [40]. Following the publication of the IOM recommendations for weight gain in pregnancy, the impact of total GWG on maternal and infant outcomes has received increasing attention. Epidemiological studies show that excessive GWG signifi- cantly increases the risk for large-for-gestational-age (LGA) infants [80, 81]. A recent study of 650 pregnant women reported that in comparison to adequate GWG throughout pregnancy, excess GWG through 20 weeks, regardless of the change in weight later in pregnancy, significantly increased the risk of LGA infants [82].
Furthermore, a physical activity intervention for healthy management of GWG found that neonates born to women with excessive GWG early in pregnancy not only exhibited greater birth weights, but had significantly more body fat at birth compared to those neonates born to women with adequate GWG or excessive GWG later in pregnancy [83]. A recent study from Overcash et al. [84] suggests that early GWG in obese women of as little as 2 pounds in the first trimester (12–14 weeks) is a strong predictor of exceeding GWG values throughout pregnancy, and that second and third trimesters have the highest relative effect on total GWG. Knabl et al. also reported similar findings in even earlier periods of 8–12 weeks [65]. These studies suggest the timing of GWG may be important for infant outcomes and, in particular, that early gestational weight gain may be more influential for infant outcomes.
Insulin resistance and glucose intolerance during pregnancy can also have effects on GWG. Typically, the risk is higher among mothers who are overweight and obese.
Complications can arise for the fetus if the mother has a persistent hyperglycemia because glucose can cross the placenta freely, in turn causing hyperglycemia in the fetus as well. This process is termed “fuel-mediated teratogenesis”; fetal hypergly- cemia leads to hyperinsulinemia and can cause an increase in fetal adiposity [85].
Subsequently, this increased fetal adiposity can lead to LGA infants, which could lead to childhood obesity. In a large epidemiological study of more than 27,000 women, abnormal maternal glucose tolerance was associated with higher birth weight and length in the first 3 months of life and more weight gain from months 9–12 [86]. This same group also confirmed this from 6–12 months of life, as well, in mothers with higher fasting glucose levels from weeks 4–12 of gestation [87].
Preterm birth rates (<37 weeks of completed gestation) are also associated with GWG. In an extensive review by Viswanathan et al., there is a U-shaped association between GWG and preterm birth in that women in the lowest and highest ends have
the highest association of giving birth preterm [88]. The recent IOM guidelines state that there is some evidence that the increased risk of preterm birth associated with a higher rate of GWG was greater with increasing BMI [40]. However, most data on this topic are still mixed as to whether preterm births arise from excessive or inad- equate GWG.
Excessive GWG can lead to more long-term consequences in the child. Sewell et al. found an association between higher GWG and higher fat mass in newborn infants [89]. Another study from the same group found that in a total of 415 women, GWG directly associates with FM at birth [90]. This was also confirmed in other studies that children born to mothers who enter pregnancy overweight or obese have significantly more adiposity at birth [91, 92]. Furthermore, rapid weight gain during infancy is also related to the development of obesity later in life [93, 94]. Longitudinal studies indicate maternal adiposity has a positive influence on adiposity at 1, 2, 9, and 30 years into life [95–98].
Inadequate GWG
The initial goal of the IOM in 1990 was to assure adequate GWG in order to prevent complications of low fetal growth and negative outcomes associated with small-for- gestational-age (SGA) infants. Since obesity has become more of an epidemic in recent decades, the focus has shifted toward avoiding excessive GWG. Nonetheless, there is evidence showing that inadequate GWG can have negative outcomes on fetal health as well. It is well established that inadequate GWG increases the risk for SGA infants [99, 100].
One of the most severe adverse outcomes in SGA infants is neurodevelopment.
A few studies found that SGA children performed worse in school than gestational age-matched controls at 10 years of age and also had a slightly lower mean IQ at 5 years of age [101–103]. Although findings on this topic tend to be inconsistent, the recent IOM guidelines report that SGA is associated with minimal neurologic dys- function, but no major handicaps (e.g., cerebral palsy).