Obesity in pregnancy: Risks and interventions by gestational stage
Gestational diabetes, preeclampsia, prolonged hospitalization—these are just a few of the complications that may affect obese gravidas. Here, the authors present a rundown of what to look for when treating this unique population.
What are the reasons for this? For one, obesity and pregnancy are both associated with increased insulin resistance. The combination of these 2 conditions can overwhelm the pancreas and unmask any small abnormality in its ability to secrete insulin.
The pathophysiology of preeclampsia is less clearly understood and, therefore, so is its link with obesity. However, Stone et al13 theorized that the relationship between obesity and hyperlipidemia is what leads to preeclampsia. Hyperlipidemia damages endothelial cells through lipid peroxidases. This damage leads to increased vasoconstriction and platelet aggregation.
The obese gravida should undergo early glucose screening along with regular blood pressure measurements.
For the obese patient, clinicians should place increased emphasis on preeclampsia and gestational diabetes screening and prevention. The obese gravida should undergo early glucose screening along with regular BP measurements. Several studies have investigated possible interventions for women at high risk for pregnancy-induced hypertension. In 1 systematic review of 41 randomized controlled trials, aspirin was associated with a 15% reduction in the relative risk of preeclampsia (95% confidence interval, 0.78 to 0.92), with no increase in adverse outcomes.14 Another systematic review found that calcium supplementation (at least 1 g per day) can reduce the risk of preeclampsia by 30%.15 Still, no trials have examined aspirin or calcium supplementation among obese patients; the clinician must therefore weigh the benefits of these prophylactic measures.
Deep venous thrombosis. Along with preeclampsia and gestational diabetes, deep venous thrombosis and its complications—which include maternal mortality—are seen more frequently in the obese patient. One 10-year review in Minnesota looked at weight distributions for mothers who died. Researchers found that 12% of this population, compared with 2% of the control group, had prepregnancy weights greater than 200 lb.16 The leading cause of death among the obese group was pulmonary embolus.
Fetal death. A large, population-based cohort study reported a relationship between maternal obesity and fetal death.17 Among nulliparous women in this study, the risk of late fetal death (stillbirth occurring at 28 weeks’ gestation or later) increased as the BMI rose. The obese woman was 4 times as likely to have a late fetal death as the lean woman. In parous women, the risk was only increased in the obese BMI category—rather than in all classifications of BMI. After excluding women with hypertensive diseases and diabetes, the association persisted. Huang et al18 supported these findings by identifying maternal prepregnancy weight greater than 68 kg as a risk factor for unexplained fetal deaths, even after controlling for maternal diabetes and hypertensive disease.
Intrapartum
Labor induction. Obesity is associated with an increased likelihood of labor induction. Gross et al19 reported that 15% of obese women (over 90 kg) had labor induced, compared with 8% of controls (P<.0001 ekblad and grenman>20 also showed a significantly higher induction rate in obese patients and those with excessive weight gain during pregnancy.
Cesarean delivery. The effect of obesity on cesarean delivery rates has been debated, but most studies indicate a direct correlation (TABLE 2). Kaiser and Kirby21 showed that even among low-risk patients in a nurse-midwifery service, a BMI above 29 was associated with a 3-fold to 4-fold increase in cesarean delivery. A study by Cnattingius et al17 demonstrated that the effect of BMI on cesarean rates also was influenced by maternal height: Short obese women had the highest cesarean rate (36%), followed by (in decreasing order) short, lean women; tall, obese women; and, finally, tall, lean women.
VBAC. These findings raise a natural follow-up question: What is the success rate of vaginal birth after cesarean (VBAC) among obese parturients? Among 30 women weighing more than 300 lb at conception, Chauhan et al22 noted a VBAC success rate of less than 15%.This is much lower than the general success rate of 60% to 80% quoted in the ACOG practice bulletin on VBAC.23 Grobman et al24 reported that VBAC is cost-effective among women with 1 prior cesarean delivery only if the success rate is above 40%; it is therefore worth pondering whether VBAC should be attempted in overweight patients.
TABLE 2
Obesity and cesarean delivery rates
| AUTHORS | NUMBER OF SUBJECTS | OBESITY DEFINED AS | RATE OF CESAREAN DELIVERY | COMMENTS |
|---|---|---|---|---|
| Baeten et al, 200112 | 9,817 | BMI≥30 | Increased | — |
| Kaiser and Kirby, 200121 | 452 | BMI≥29 | Increased* | Population was low risk without prior cesarean. |
| Kumari, 200137 | 188 | BMI >40 | Increased* | Elective* and emergency cesareans examined. |
| Steinfeld et al, 200038 | 168 | BMI≥29 | Increased* | Excluded elective cesareans and those performed due to fetal malpresentation and previa. |
| Jensen et al, 199939 | 163 | BMI≥30 | Increased | Excluded patients with prior cesarean. |
| Ranta et al, 199540 | 53 | BMI≥30 | Increased | — |
| Issacs et al, 19949 | 117 | >300 lb | Increased* | Primary and repeat cesareans examined. |
| Hood and Dewan, 199325 | 117 | >300 lb | Increased* | Elective and emergency* cesareans examined. |
| Ekblad and Grenman, 199220 | 77 | ≥20%† | Increased | Emergency cesareans examined. |
| Perlow et al, 199235 | 111 | >300 lb | Increased* | Primary* cesareans and those performed due to fetal distress examined. |
| Pongthai, 199041 | 741 | ≥80 kg | Increased* | Primary and repeat* cesareans examined. |
| Johnson et al, 198730 | 588 | >113.6 kg | Increased* | Primary cesareans examined only. |
| Garbaciak et al, 198536 | 1,889 | >120%† | Increased* | Primary cesareans examined only. |
| Gross et al, 198019 | 279 | ≥90 kg | Increased | Repeat cesareans omitted. |
| Edwards et al, 197827 | 208 | >50%‡ | Increased | — |
| BMI = body mass index | ||||
| *Significant increase | ||||
| †Over ideal body weight for height | ||||
| ‡Above standard weight for height on the Metropolitan Life Insurance tables | ||||
