Issues related to weight management during pregnancy among overweight and obese women

Pregnancy & obesity

The obesity epidemic, now evident throughout the industrialized world, has significantly impacted both the short- and long-term health of pregnant women and their offspring. In 2003–2004, approximately 52% of women of childbearing age in the USA were overweight (body mass index [BMI] 25–29.9 kg/m²) or obese (BMI > 30 kg/m²) [1]. Along with the rising prevalence rates of adult obesity, birth weights and the proportion of macrosomic infants have also climbed over the past 30 years [2].

Growing evidence associates overweight and obesity with negative outcomes for fertility, pregnancy and delivery [2–5]. The American College of Obstetricians and Gynecologists (ACOG) has acknowledged the problems associated with obesity in pregnancy [6]. Unfortunately, the number of studies addressing the control of weight prior to conception and during pregnancy is small, and the interventions have not been particularly effective for women with pregravid obesity. In this editorial we will first address the clinical implications for the management of overweight and obese pregnant women as pertains to obstetrics care. Second, we will address issues related to clinical weight management before, during and after pregnancy. Finally, we will comment on the directions of future research in these areas.

Pregnancy & complications due to overweight & obesity

Following this increasing prevalence of obesity among women of reproductive age and pregnant women, we have realized that overweight and obesity negatively impact almost all aspects of reproduction, from impaired fertility to maternal and fetal risks during pregnancy, to obstetrical complications [7–9]. The impact even extends beyond the neonatal period for the offspring [10]. For many of these adverse outcomes, there appears to be a dose–response effect, with the magnitude of these risks increasing with higher BMI.

Fetal outcomes

Once women successfully conceive, overweight and obesity increase the risk of spontaneous abortion both in pregnancies conceived after infertility treatment [11–13] and pregnancies conceived spontaneously [14]. Obesity also appears to be a risk factor for congenital anomalies, especially neural tube defects (NTDs) and congenital heart defects [15,16]. However, as pregestational diabetes is associated with both obesity and these congenital anomalies, it raises the question of whether these fetal anomalies are truly due to maternal obesity or due to undiagnosed pregestational Type 2 diabetes.

Not only are birth defects more common in overweight and obese women, they are also more difficult to diagnose and more likely to be missed by prenatal diagnosis modalities. Adequate visualization of fetal anatomy by ultrasound is impaired in obese women and the fetal structures that are most likely to be suboptimally visualized are the heart and the spine [17,18]. Additionally, obesity can impair the performance of maternal serum-α fetoprotein (MSAFP) as a screening tool for NTDs, even when MSAFP values are adjusted for maternal weight [19]. When these congenital anomalies are missed by prenatal diagnosis, women lose the possibility of terminating the pregnancy and postnatal diagnosis can adversely affect neonatal outcomes (when compared with antenatally diagnosed congenital anomalies) [20,21]. Finally, several studies have now shown that maternal obesity is an independent risk factor for intrauterine fetal deaths, both unexplained [22,23] and those possibly caused by placental dysfunction [23,24].

Pregnancy complications

During pregnancy, overweight and obese women are at an increased risk of developing gestational hypertension, preeclampsia, gestational diabetes and venous thromboembolism [8,9,25]. Preeclampsia is one of the leading causes of maternal morbidity and mortality, as well as fetal morbidity and mortality, and is one of the most common causes of indicated preterm delivery. Gestational diabetes increases the risks of macrosomia, shoulder dystocia and cesarean section.

Delivery outcomes

Labor induction rates appear to be higher in obese women [8,26]. The reasons for this are not completely understood but are linked to higher rates of prepregnancy comorbidities, increased rates of gestational hypertension, preeclampsia and gestational diabetes and, possibly, to increased risk of post-term pregnancy [26]. Obesity has a significant impact on the mode of delivery, with the rate of cesarean section being higher in overweight and obese women [8,9,26] and increasing in a dose–response manner as BMI increases [9,27].

Several factors probably interact to lead to this increased cesarean section rate: higher rates of labor induction, higher birth weights and rates of macrosomia and decreased contractility, the last of which has recently been demonstrated in vitro in myometrium obtained from obese women [28]. Of note, this increased risk of cesarean section is also present in women in spontaneous labor [27]. When obese women are delivered by cesarean section, they are at increased risk of operative and postoperative complications, including excessive blood loss, endometritis, wound breakdown and infection, and thromboembolic events [8,29–31]. Finally, not only are obese women at increased risk of cesarean delivery in the first place, if they attempt a vaginal birth after cesarean section (VBAC), their success rate is lower than that of normal-weight women [32].

Anesthesia difficulties and complications are also more common in the laboring obese woman. Epidural and spinal can be more difficult and require multiple attempts due to body habitus, which leads to higher failure rates. Thus, when obese women require cesarean section, they are more likely to require general anesthesia and intubation; difficult intubations and respiratory complications are also increased in obese women [33]. Adequate fetal monitoring can also pose a challenge in the laboring obese woman: in the same way as maternal obesity limits ultrasound visualization, it can interfere with obtaining a reliable fetal heart rate tracing by external monitoring.

It is of concern that overweight and obese women have a higher risk of embolism, pregnancy-induced hypertension and hemorrhage, the three conditions identified by the latest report on maternal mortality as the leading causes of pregnancy-related death [34].

Neonatal outcomes

Maternal weight impacts neonatal outcomes in several ways. There have been reports of higher preterm delivery rates in obese women [7,9,35], but most of these preterm deliveries are probably indicated due to maternal complications, such as preeclampsia, rather than being due to spontaneous preterm birth. Regardless of the etiology, these premature infants require more intensive care and a proportion of the survivors will have long-term sequelae, including chronic respiratory problems and neurodevelopmental impairments [36].

Maternal prepregnancy weight and weight gain during pregnancy both correlate with birth weight but the correlation is stronger with prepregnancy weight. Obesity is a risk factor for macrosomia [9,26], as are pregestational and gestational diabetes, which are also more common in overweight and obese women. In the immediate postnatal period, macrosomic infants are at higher risk of birth trauma and metabolic issues, including hypoglycemia and hyperbilirubinemia. Shoulder dystocia has also been reported to be increased in obese women [26,37]; however, some of this association appears to be explained by the fact that obese women have higher rates of diabetes and macrosomic infants, which are risk factors for shoulder dystocia.

The impact of the in utero environment for the offspring of obese women appears to extend far beyond the neonatal period. There is increasing evidence that higher birth weight and macrosomia are associated with higher rates of childhood, adolescent and adult obesity [10,38]. Additionally, maternal obesity in early pregnancy has been associated with a twofold increase in childhood obesity, while actual birth weight had only a minimal impact on this risk [39]. When studying the impact of maternal overweight and obesity on these adverse outcomes, pregravid or early pregnancy BMI appears to be a much stronger risk factor than excessive weight gain during pregnancy, thus underscoring the importance of preconception counseling and intervention.

Current weight gain recommendations during pregnancy

In 1990, the Institute of Medicine (IOM) recommended that average-weight women (BMI 19.9–26.0 kg/m²) gain approximately 25–35 lbs (11.4–15.9 kg), overweight women (BMI 26.1–29.0 kg/m²) gain 15–25 lbs (6.8–11.4 kg) and obese women (BMI > 29 kg/m²) gain no more than 15 lbs (6.8 kg) during the course of pregnancy [40]. The purpose of these guidelines was to prevent low-birth-weight infants, but they do not give much consideration to the issue of excessive weight gain during pregnancy and its associated negative consequences [2,3]. A substantial proportion of pregnant women are believed to surpass the IOM’s recommendations of adequate weight gain, with the mean weight gain of overweight and obese women exceeding the guidelines [41].

Other professional groups have issued recommendations on the management of body weight during pregnancy. For example, the ACOG recommends weight loss before pregnancy and evidence suggests that reducing weight before conception may have the largest positive effect on the intrauterine environment [2]. To help obstetrician–gynecologists, midwives, family physicians and other prenatal care providers with these issues, the National Institute for Diabetes, Digestive, and Kidney Diseases (NIDDK) has published nutrition guidelines for pregnancy [42]. These guidelines suggest that average-weight women increase intake by 300 kcal/day in the second and third trimesters. It is unclear, however, what percentage of prenatal care providers are aware of, let alone use, these recommendations in daily practice. Furthermore, the guidelines are incomplete. The NIDDK recommendations do not include guidance for women who are overweight or obese pregravid, who now make up 52% of women between the ages of 20 and 39 years [1], only instructing that they consult with their healthcare providers for more specific instructions.

Unfortunately, obstetrician–gynecologists, as with primary care practitioners, may be reluctant to provide guidance on weight management because of issues related to perceived competence, skepticism about the effectiveness of weight loss treatment or concerns regarding insurance reimbursement [43]. Furthermore, approximately half of pregnancies in the USA are unplanned [44], and even when their pregnancy was planned many women do not present for obstetric care until the second trimester in the pregnancy. As a result, the window of opportunity for obstetician–gynecologists to recommend a weight loss program for their patients before pregnancy, or a weight maintenance program during pregnancy, may be quite small.

The ACOG also suggests that overweight and obese women receive nutritional and exercise guidelines in the postpartum period, particularly in order to achieve maximum weight loss before conceiving again. While this recommendation has intuitive appeal, the empirical evidence is inconclusive regarding exactly how much weight is retained after birth. A review of nine studies suggested that the average postpartum weight retention was 0.5–3 kg but could be as high as 17.7 kg [45]. Aside from an absolute weight gain, a more consistent correlation is that women who gain more weight during pregnancy will retain more weight both in the short- [46] and long-term [47,48] postpartum, which further highlights the need to manage weight gain during pregnancy.

Women of reproductive age with extreme obesity (BMI ≥ 40 kg/m²), who comprise 8% of the US population [1], have been particularly neglected in the existing guidelines. Many of these women are now undergoing bariatric surgery, particularly laparoscopic adjustable gastric banding [49,50]. The ACOG warns that women who have undergone this procedure may become pregnant unexpectedly and that they should try to prevent pregnancy in the first 12–18 months following surgery. They should receive evaluation for nutritional deficiencies, particularly vitamin B12 and folate. Early data suggest that bariatric procedures seem to decrease the risks of gestational diabetes, hypertensive complications, macrosomia and cesarean section, but more research is needed to assess the impact of gastric bypass surgeries, the more common procedures in the USA [51–53].

Ineffectiveness of current interventions

There is a paucity of studies addressing the management of excess weight gain during pregnancy and formal weight loss programs in the postpartum period. While the efficacy of behavioral and pharmacological weight control methods has been studied extensively [43,54,55], to our knowledge, only two controlled studies have been published addressing weight control during pregnancy.

The first study randomized 120 women with a pregravid BMI greater than 19.8 kg/m² to a behavioral intervention or control group. The behavioral intervention consisted of weighing during clinic visits, coupled with the dissemination of written information about weight gain, exercise and healthy eating for pregnancy [56]. Women who remained within the IOM weight gain guidelines were encouraged to continue with their adherence to the program, while women who exceeded the guidelines received behavioral counseling and additional nutritional information. The control participants received standard nutritional counseling by staff on appropriate diet and vitamin supplementation. While average-weight women who received the intervention were less likely to exceed the guidelines (33 vs 58%, respectively), overweight and obese women receiving the intervention were not less likely to exceed the guidelines. In fact, there was a nonsignificant likelihood for more overweight women in the intervention group to exceed the guidelines than those in the control group (59 vs 32%, respectively; p = 0.09).

The second study tested the efficacy of a psychoeducational intervention for average and overweight women, consisting of mailings about healthy weight gain, nutrition and exercise during pregnancy (n = 179), as compared with similar controls with no additional care (n = 381) [57]. Unfortunately, there were no significant differences in excessive weight gain between the intervention and control groups; 41 and 45% gained more than the guidelines, respectively. There was, however, a positive effect for participants with low income, with 33% not exceeding guidelines in the intervention compared with 52% of the control group. There was no effect for weight status.

Clearly, these results are suboptimal. Both interventions were ineffective among overweight and obese women. These discouraging findings indicate that much more careful study and creativity are needed to address this pervasive problem. One possible area of interest that has received preliminary attention is the application of low glycemic index guidelines to healthy eating during pregnancy. Clapp has reported higher rates of excess weight gain and larger infants and placentas among pregnant women on high glycemic index diets compared with those on low glycemic index diets [58]. Those on the low glycemic index diets also exhibited a blunting of the usual increases of insulin in mid-to-late pregnancy. These studies have consisted of small samples and more work is needed to determine whether these findings can be replicated.

As with studies of weight gain during pregnancy, very few investigations have examined the efficacy of weight loss during the postpartum period. One study randomly assigned women up to 1 year postpartum, who were at least 6.8 kg above their pregravid weight, to a behavioral intervention (n = 47) or a control condition (n = 43) [59]. The intervention consisted of multiple mailings, biweekly phone calls and two behavioral modification sessions that focused on reduction of fat and overall calories and increase in physical activity. The control group received a brochure briefly addressing healthy eating and exercise. This intervention was effective and showed a significantly greater reduction in weight and a higher likelihood of reaching pregravid weight.

More recently, Lovelady and colleagues studied a postpartum weight loss intervention among lactating women, a special population often neglected by other studies in this area [60]. A total of 27 women received an energy deficit diet of 500 kcal/day and an exercise program, while 21 women received standard postpartum care. The diet and exercise group lost a significantly higher percentage of weight, 6.8%, than the control group, who lost only 1%. Importantly, those in the intervention did not report a decrease in their milk supply or fussiness in their babies. There were differences in micronutrients between the groups, with the intervention group showing lower calcium and vitamin D intake, suggesting a need for supplementation with this type of diet.

The modality of the intervention is also very salient to the success of a program. O’Toole and colleagues compared a structured diet and physical activity program with a self-directed program [61]. As with the studies above, attrition was a problem with only 23 out of 40 individuals completing the programs. However, there was a significant weight loss of 7.3 kg in the structured program at 1 year postpartum compared with a nonsignificant drop of 1.3 kg in the self-directed group.

In sum, intervention programs that focus on preventing excessive weight gain during pregnancy have been less effective for overweight and obese women than structured postpartum weight loss programs, and all programs have high drop-out rates. As intervention at both stages remains important, more work is needed to find creative ways to manage weight successfully in this population.

Implications for future treatment

Owing to the limited time of the obstetrician, a team approach is likely to be the most effective model for imparting the appropriate information to overweight and obese women. This team may include the obstetrician–gynecologist or prenatal care provider, a nutritionist, a physical trainer who has experience with exercise during pregnancy and a psychologist familiar with behavioral weight control treatments.

There are very real obstacles to implementing structured weight loss programs with pregnant women and even more so with postpartum women. These obstacles include the enormous time commitment in caring for a newborn, sleep disruption, sleep debt and postpartum depression, all of which may influence motivation for weight loss. These factors limit the time available to attend intervention sessions, plan nutritious meals and schedule time for exercise. Exercise may also be uncomfortable for many women, not just in the initial weeks while recovering from childbirth, but also in the longer term if they are lactating. While group-based behavioral treatment over a 4–6-month period is considered the ‘gold standard’ of behavioral weight control interventions, this treatment modality may be difficult if not impossible for new mothers. Thus, researchers and clinicians need to be innovative in their approach to weight management and probably need to adapt behavioral weight control strategies to postal mailings, phone-based consultations, internet-based programming, text messaging and e-mails.

In sum, the effect of obesity on pregnancy is pronounced and increasingly prevalent. It is time for more controlled trials of weight control interventions at all stages of reproduction – prepregnancy, during pregnancy and postpartum – in order to mitigate the effects of pregnancy on increasing or maintaining obesity in mothers, and on the wellbeing of their offspring. Failure to address these issues increases the likelihood that we will continue to pass on the debt of obesity to future generations.