Obese patients should be advised to avoid excessive weight gain in pregnancy.
Dr Lockwood, Editor-in-Chief, is Dean of the Morsani College of Medicine and Senior Vice President of USF Health, University of South Florida, Tampa.
The obesity epidemic now affects a third of US adults including pregnant women.1,2 Adverse pregnancy outcomes attendant obesity include increased rates of congenital anomalies, stillbirth, preeclampsia, preterm birth, gestational diabetes, as well as both fetal growth restriction and macrosomia.3,4 Macrosomia is, in turn, linked to increased risks of both shoulder dystocia, which can lead to permanent brachial plexus injuries, and cesarean delivery, which in obese patients is accompanied by elevated rates of venous thromboembolism and wound complications. Moreover, obesity in pregnancy has serious long-term health consequences for both mother and offspring.4
Conversely, it has also been long-appreciated that underweight mothers, and/or those with low gestational weight gain, are at increased risk for spontaneous preterm birth and low-birth-weight (LBW) infants. In 2009, a committee of the Institute of Medicine (IOM) attempted to thread the needle between these risks with a revised set of guidelines for gestational weight gain among obese gravidas. The IOM recommended that obese women (body mass index [BMI] > 30) gain 11 to 20 lb (5–9 kg).5 Their recommendation came under immediate fire, with some (including me) opining that lesser weight gain strategies might be beneficial in select obese patients.6 A number of experts have gone further and endorsed weight loss during pregnancy among such patients. Recent studies of weight loss among severely obese patients either during or before pregnancy, due to diet or bariatric surgery, respectively, demonstrate clear benefits but some potential risks.
Bogaerts and colleagues assessed pregnancy outcomes in a cohort of more than 18,000 obese Flemish women with live-born singleton gestations according to degree of obesity and extent of gestational weight gain or loss.7 Obesity was broken into 3 classes: class I (BMI 30 to 34.9), class 2 (35 to 39.9) and class III (≥ 40). Weight change categories were:
1. greater weight loss (≥5 kg);
2. lesser weight loss (between 0 and 5 kg);
3. low weight gain (0 to 5 kg);
4. adequate weight gain (≥5 to ≤9 kg); and
5. excessive weight gain (>9 kg).
Birth outcomes included gestational hypertension, LBW infants (≤ 2500 g), small-for-gestational age (SGA; birthweight < 10th percentile), macrosomia (≥ 4000 g at birth), large-for-gestational age infants (LGA; >90th percentile), emergency cesarean delivery, and neonatal intensive care unit (NICU) admission. Among this cohort, only 4.7% reported any degree of weight loss, 13.8% had low weight gain, 28.3% had adequate weight gain, and an astonishing 53.1% had excessive weight gain. Weight loss occurred among only 3.2% of class I, 7% of class II, and 13.4% of class III patients. In univariate analysis, the prevalence of adverse outcomes, except SGA, significantly increased with increasing obesity class. Conversely, gestational hypertension, macrosomia, LGA, and emergency cesarean delivery all decreased with decreasing categories of gestational weight gain. However, the prevalence of LBW and SGA decreased with increasing categories of weight gain.
When Bogaerts et al performed an adjusted multivariate analysis, they found that among class I gravidas, weight loss and low gestational weight gain were associated with a decreased odds ratio (OR) for gestational hypertension of 0.31 (95% CI: 0.11–0.84) for those with greater weight loss, 0.46 (95% CI: 0.21–0.99) for those with lesser weight loss, and 0.71 (95% CI: 0.54–0.93) for those with low weight gain, compared with those achieving “adequate” weight gain. Similar beneficial trends were observed in class II and III patients achieving greater weight loss but these did not reach statistical significance, likely due to the low numbers of affected patients achieving that degree of weight loss. The occurrence of emergency cesarean delivery was reduced among class II patients with an OR of 0.24 (95% CI: 0.07–0.78) for greater weight loss patients, 0.5 (95% CI: 0.26–0.97) for lesser weight loss patients and 0.55 (95% CI: 0.38–0.79) for those with low weight gain.
Macrosomia was also reduced in all 3 obesity classes when there was weight loss ≥ 5 kg with an OR of 0.47 (95% CI: 0.24–0.9) for class I, 0.32 (95% CI: 0.12–0.9) for class II and 0.15 (95% CI: 0.05–0.49) for class III patients. Macrosomia was also reduced in each class among those in the lesser weight loss and low weight gain categories but with variable degrees of statistical significance. Similar findings were noted for LGA. Importantly, weight loss had no statistically significant effect on LBW, SGA, or NICU admissions in any class of obesity. Conversely, excessive weight gain significantly lowered the risk of SGA only among class II patients (OR of 0.62; 95%CI: 0.53–0.72) and significantly increased rates of gestational hypertension in class I and II patients. Thus, the authors concluded that weight gain lower than IOM recommendations among obese gravidas with singleton gestations resulted in reduced risks of gestational hypertension, emergency cesarean delivery, macrosomia, and LGA infants. Moreover, among those who lost weight, all these adverse outcomes were reduced without an increase in SGA and LBW.
In contrast, Catalano and associates conducted a prospective cohort study of 1053 overweight and obese patients with singleton term pregnancies and observed that weight loss or weight gain ≤5 kg was associated with SGA (adj OR of 2.6; 95% CI: 1.4–4.7).8 While neonates of women who lost or gained ≤5 kg had lower birth weight and fat mass, they also had less lean mass and a smaller length and head circumference. However, a growing number of recent studies suggests greater benefits and lesser risks for weight gain lower than than what is recommended in the IOM guidelines. Swank and colleagues studied the effects of gestational weight gain compared with IOM guidelines in a retrospective cohort using California birth certificate and patient discharge data.9 Among 1034 obese women studied, those with weight gain below IOM guidelines had fewer macrosomic infants (OR of 0.50, 95% CI 0.32–0.77) without an increase in preterm births or LBW. In contrast, excessive weight gain increased rates of gestational hypertension (OR 1.96, 95% CI 1.26–3.03) and cesarean delivery (OR 1.40, 95% CI 1.00–1.97).
Turong et al conducted a US population-based retrospective cohort study of obese nulliparous women with term singleton vertex births and observed that weight gain in excess of IOM guidelines, particularly when ≥20 lb, increased the risk of preeclampsia, eclampsia, cesarean delivery, and various adverse neonatal outcomes including low Apgar scores, seizures, and the need for ventilation.10 Conversely, obese gravidas who gained less than IOM guidelines had fewer hypertensive disorders of pregnancy and obstetric interventions but were more likely to have SGA neonates (aOR of 1.55; 95% CI: 1.52–1.59).
There is also evidence that excessive weight gain may have different long-term effects on offspring, depending on the trimester in which weight gain takes place. Karachaliou and colleagues observed that excess weight gain in the first trimester was associated with increased risk of overweight/obese and hypertensive children at age 4 years whereas excess weight gain during the second and third trimesters was associated with LGA infants but not childhood obesity.11
While Bogaerts and colleagues found weight loss or at least lesser weight gain in obese gravidas to be clearly beneficial, fewer than 20% of such patients achieved such dietary discipline, while more than half had excessive weight gain.7 This finding underscores the difficulty of treating obesity in pregnancy. The use of preconceptional bariatric surgery in patients with severe obesity or obese patients with related comorbidities has now gained favor. However, the effects of these procedures on subsequent pregnancies have been poorly studied. A recent large Swedish study sheds light on the benefits and potential risks of bariatric surgery in subsequent pregnancy.12 Johansson and associates mined 2 large registries-the Scandinavian Obesity Surgery and Swedish Medical Birth registries-to identify 670 pregnancies occurring in women with prior bariatric surgery for whom pre-surgery weights were available. They conducted a nested case-control study matching these patients with up to 5 controls for presurgical BMI and potential confounders and then compared outcomes including gestational diabetes, LGA, SGA, preterm birth, stillbirth, neonatal death, and congenital anomalies. Compared to controls, bariatric surgery patients had lower risks of gestational diabetes (6.8% vs 1.9%; OR 0.25; 95% CI: 0.13–0.47), and LGA infants (22.4% vs 8.6%; OR 033; 95% CI: 0.24–0.44). There were no differences between the groups in preterm delivery rates.
However, compared with controls, bariatric surgery patients had higher rates of SGA infants (7.6% vs 15.6%; OR of 2.20; 95% CI: 1.64–2.95) and, more ominously, a trend toward higher rates of perinatal mortality, ie, stillbirth plus neonatal deaths (0.7% vs 1.7%; OR of 2.39; 95% CI: 0.98–5.85). Interestingly, gestational weight gain had no effect on these associations. Several confounders may explain the higher rate of SGA and trend toward a higher perinatal mortality rate among the bariatric surgery patients. For example, they had more preoperative medical comorbidities than controls and 98% had metabolically challenging gastric bypass rather than more-benign gastric banding procedures. Interestingly, the longer the surgery-to-delivery date interval, the higher the rate of SGA, and the greater the surgically induced reduction in BMI, the lower the risk of LGA.
Where does all this leave us? First, most obese gravidas gain substantially more weight than recommended under IOM guidelines, and the combination of obesity and excessive weight gain results in substantially excess maternal and perinatal morbidity and likely mortality. Second, gestational weight gain less than IOM recommendations, and possibly moderate (< 5 kg) weight loss, confer clear maternal and neonatal health benefits but the degree of optimal weight loss is unknown and excess weight loss may increase the risk of SGA, possibly smaller head circumferences and, if extreme, potentially perinatal mortality. Third, it is unlikely that current counseling and lifestyle modification techniques are adequate to achieving these gestational weight goals.
Thus, extensive studies are needed to determine:
1. how to enhance diet adherence in obese gravidas;
2. the optimal weight gain or weight loss targets that confer maximum perinatal and long-term health benefits with minimal risks; and
3. how such targets vary with maternal obesity class.
Until such studies are completed, it seems reasonable to encourage obese gravidas to at least follow current IOM guidelines and perhaps attempt to gain only 0 to 5 kg. Such counseling is best done in concert with a nutritionist who maintains regular and frequent contact with the patient, and should be accompanied by a tailored exercise regimen. However, it is far from certain whether such an approach will prove practical, successful, or cost-effective in real-world applications. For bariatric surgery patients, surveillance for fetal growth restriction and oligohydramnios seems reasonable after 28 weeks and weight gain within but not above IOM recommendations seems in order. Of course, the best strategy by far is for obese women to achieve a BMI < 28 prior to pregnancy by exercise and dieting, but we all know how hard that is!
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