Obesity and Pregnancy

Preconception

Weight loss before pregnancy, whether achieved via surgical or nonsurgical methods, has been shown to be the most effective intervention to improve medical comorbidities, especially diabetes and hypertension. Obese women who have even small weight reductions before pregnancy may have improved pregnancy outcomes if they can avoid excessive weight gain once pregnant.[3, 4] Unfortunately, many women present for obstetrical care with an elevated body mass index (BMI).

It is recommended that women with a history of bariatric surgery wait 12-24 months before conceiving so that the fetus is not exposed to a rapid maternal weight loss environment and so that the patient can achieve full weight loss goals. Unfortunately, pregnancy may occur prior to this recommended time frame. The number of bariatric surgical procedures performed annually has dramatically increased, with many performed in reproductive-aged women.[4] Obstetric care providers can expect to manage increasing numbers of pregnancies in women with a history of bariatric surgery. (Refer to the Medscape article on bariatric surgery for additional information.)

Calculating BMI and weight gain counseling

A thorough history taking and physical examination are completed at the first obstetrics visit. A woman’s BMI is also calculated at the initial visit. Obesity class I is defined as a BMI of 30-34.9 kg/m2, obesity class II as a BMI of 35-39.9 kg/m2, and obesity class 3 as a BMI greater than or equal to 40 kg/m2. This BMI is used to provide counseling guided by Institute of Medicine (IOM) recommendations for gestational weight gain during pregnancy. The IOM guidelines recommend a total weight gain of 15-25 lb for overweight women and 11-20 lb for obese women.[5]

These recommendations have some limitations. As mentioned earlier, a pregnancy-specific definition of obesity has not been standardized; thus, the pre-pregnancy BMI is typically used. BMI is imperfect, as it does not tell the whole story about the composition of a patient's body. One also needs to realize that weight gain is used simply as a proxy measure for the nutritional status of the woman. It is the actual nutritional quality of food intake that is critical and not simply the act of gaining weight. Women tend to gain the amount of weight they feel that they should. Unfortunately, obese women expect that a weight exceeding IOM recommendations is appropriate and in turn gain in excess of the recommendations.[6]

Nutritional status before and during early pregnancy may play an important role in ensuring successful pregnancy outcomes. Preconceptional and periconceptional intake of vitamin and mineral supplements is associated with a reduced risk of low birth weight and/or small-for-gestational-age infants and preterm deliveries.[7]  Although inadequate weight gain and weight loss have been associated with small-for-gestational-age infants and even decreased lean body mass in the neonate, some studies have shown that in the pregnant woman with morbid obesity (BMI >40 kg/m2), weight gain of less than 10 lb and even weight loss in the setting of good balanced meals with appropriate caloric and nutritional intake may be acceptable.[8]  Careful evaluation of the patient's diet is key in this situation.

Increased maternal and fetal risks

Obese pregnant women are at increased risk for many maternal and perinatal complications, and the risks are amplified with increasing degrees of maternal obesity. For this reason, a detailed history and physical examination are critical at the initial obstetrics visit, with ongoing monitoring as needed.

Obese women are at increased risk for spontaneous abortion (odds ratio [OR], 1.2; 95% confidence interval [CI], 1.01-1.46) and recurrent miscarriage (OR, 3.5; 95% CI, 1.03-12.01), compared with age-matched controls.[9]  Obese women are also at increased risk for most congenital anomalies, including the following[10] :

• Neural tube defects (OR, 1.87; 95% CI, 1.62-2.15)
• Hydrocephaly (OR, 1.68; 95% CI, 1.19-2.36)
• Cardiovascular anomalies (OR, 1.30; 95% CI, 1.12-1.51)
• Orofacial anomalies, such as cleft lip and palate (OR, 1.20; 95% CI, 1.03-1.40)
• Limb reduction anomalies (OR, 1.34; 95% CI, 1.03-1.73)

The risk of gastroschisis in neonates among obese gravida, however, is significantly reduced (OR, 0.17; 95% CI, 0.10-0.30).[10]  Obese pregnant women are 40% more likely to experience stillbirth compared with nonobese pregnant women (adjusted hazard ratio, 1.4; 95% CI, 1.3-1.5).[11]  The risk directly increases with rising body mass index (BMI), to over a threefold increase for women with a BMI exceeding 50 kg/m2. The risk is even higher for Black women who are pregnant.

Unfortunately, detection of congenital anomalies by ultrasonography is significantly reduced with increasing maternal BMI. Detection of anomalous fetuses decreases with increasing maternal BMI by at least 20% in obese women, compared with normal-weight women.[12]  Obese women are not at greater risk for fetal aneuploidy; however, obesity can affect screening test performance. First and second trimester serum-based screening tests are adjusted for maternal weight; thus, obesity does not affect test performance. However, accurate nuchal translucency measurement may be more difficult to obtain in obese women.[13]

Cell-free fetal DNA screening is more likely to result in test failure or an inaccurate result in obese women because they may have a lower fetal fraction of the cell-free DNA.[14]  Given that patients with a test failure are at increased risk for genetic issues, they should receive further genetic counseling and be offered comprehensive ultrasound evaluation and diagnostic testing. Some recommend performing the cell-free fetal DNA screening further into the pregnancy (12-14 weeks) to improve the fetal fraction levels.

An increased incidence of dizygotic but not monozygotic twin gestation has been observed among obese gravidas. This association has been attributed to elevated follicle-stimulating hormone levels in obese women.[15]

Early ultrasound evaluation should be performed to establish gestational age and to determine whether there is a multifetal gestation. As mentioned above, obese women have an increased risk of fetal structural congenital anomalies. The use of the maternal navel approach may provide a better acoustic window. Obese women should be counseled about the limitations of ultrasonography in identifying structural anomalies. The increased risk of fetal cardiac malformations and the lower detection rates for congenital cardiac malformations with maternal obesity may support the use of fetal echocardiography in these pregnancies unless the detailed ultrasound assessment of the heart is optimal and normal.[16]

Although the approach to fetal aneuploidy screening in the obese gravida is the same as in the general population, patients should be counseled on the limitations. Diagnostic procedures such as amniocentesis and chorionic villus sampling are more technically challenging.

Women should receive counseling regarding potential pregnancy risks associated with obesity, including those described above. The primary weight management strategies during pregnancy are dietary control, exercise, and behavior modification. The goal is to avoid excessive gestational weight gain, which is common in obese women. Working with a nutritionist can help patients plan meals for optimum healthy gestational weight gain.[17] Pregnant women with healthy, uncomplicated pregnancies can initiate an exercise program or continue most pre-pregnancy exercise programs.[18]  Almost all drugs prescribed for weight reduction have adverse fetal effects and should not be used during pregnancy. Diet, physical activity, and weight gain or loss should all be reviewed frequently throughout pregnancy and the postpartum period.

Compared with normal-weight women, obese women are at increased risk for cardiac dysfunction, proteinuria, obstructive sleep apnea (OSA), nonalcoholic fatty liver disease, gestational diabetes mellitus, and preeclampsia. Many of these are more severe as obesity increases during pregnancy, especially once in the categories of the morbidly obese (BMI, 40-49 kg/m2) and more so with the extremely morbidly obese (BMI, 50 kg/m2 or higher). These comorbidities can be present individually or may be part of an insulin resistance complex. The increased insulin resistance that is normal during pregnancy may cause preexisting but subclinical cardiometabolic dysfunction to emerge as preeclampsia, gestational diabetes, and OSA.[19]

An association between obesity and hypertensive disorders during pregnancy has been consistently reported. Obese women should be monitored for the development of hypertensive disorders during pregnancy or for the exacerbation of preexisting hypertensive disease.

Obese women are more likely to have chronic hypertensive disorders prior to pregnancy. Although these disorders may improve during the early portion of the pregnancy, the underlying pathology will commonly manifest itself in the third trimester. In a systematic review of 13 cohort studies comprising nearly 1.4 million women, the risk of preeclampsia doubled with each 5 to 7 kg/m2 increase in pre-pregnancy BMI. This relationship persisted even after adjustment for other confounders such as chronic hypertension, diabetes mellitus, or multiple gestations.[20]  The occurrence of hypertensive disorders rises both with increasing maternal BMI and with increasing gestational age, averaging a fivefold increase for women at term with a BMI of 40 kg/m2 or higher when compared with women who have a healthy BMI while pregnant.[21]

Consider baseline quantitative urine protein, creatinine concentration, platelet count, and liver function tests, which can be useful for comparison with laboratory values later in pregnancy if the patient undergoes evaluation for preeclampsia. These baseline laboratory studies can be done at the initial obstetrics visit or at mid-second trimester (20-24 weeks). Obese women with additional risk factors for the development of preeclampsia (such as chronic hypertension, multiple gestation, nulliparity, maternal age greater than or equal to 35 years, and family history of preeclampsia) may benefit from treatment with low-dose (81 mg) aspirin for prevention.[22]  Refer to the Medscape article on pregnancy-related hypertension for additional information.

Patients may have occult type 2 diabetes mellitus if screening has not been done within a year or so prior to pregnancy. The prevalence of gestational diabetes mellitus is significantly higher in obese women than in the general obstetrical population, and the risk rises with increasing maternal weight and BMI (OR, 2.8; 95% CI, 2.54-3.08).[23] Routine screening for gestational diabetes is performed at 24-28 weeks of gestation. Early pregnancy screening for glucose intolerance (gestational diabetes or overt diabetes) should be based on risk factors, including maternal BMI of 30 kg/m2 or greater, known impaired glucose metabolism, previous gestational diabetes, family history, and polycystic ovary syndrome (PCOS).

The best test for early screening is not clear. Many obstetric care providers start with a 50-g glucose challenge test. The testing used to diagnose type 2 diabetes in nonpregnant individuals could be used for early pregnancy screening. Measurement of hemoglobin A1c also can be used but may not be suitable to use alone because of decreased sensitivity compared with oral glucose tolerance tests (GTTs).[24]  Some will screen with A1c at the initial obstetrics visit, and if the value is 5.8% or greater, consider a GTT or other appropriate additional testing for diagnosis. If the initial early diabetes screening result is negative, a repeat diabetes screening is performed at 24-28 weeks of gestation. Refer to the Medscape article on diabetes management in pregnancy for additional information.

Obstructive sleep apnea (OSA) may be precipitated by or exacerbated during pregnancy and may increase the risk of preeclampsia and gestational diabetes mellitus.[25]  Pregnant women with OSA are also at increased risk for eclampsia, cardiomyopathy, pulmonary embolism, and in-hospital mortality.[26] Additional possible adverse pregnancy outcomes include cesarean section as well as having low birth weight, preterm, and small for gestational age infants.[27, 28]

Therefore, screening for OSA by history should be done and sleep studies ordered as indicated. Obese women should be screened for OSA at the first prenatal visit. Women with suspected OSA due to reported snoring, excessive daytime sleepiness, witnessed apneas, or unexplained hypoxia should be referred to a sleep medicine specialist for evaluation and possible treatment. Refer to the Medscape article on sleep apnea for screening tools and further information.

The severely obese patient (BMI of >40 kg/m2) is at greater risk for cardiopulmonary dysfunction. Some experts recommend potentially obtaining a baseline echocardiogram and pulmonary lung function studies early in pregnancy. However, these are not yet considered a standard of care.

If pregnancy occurs before the recommended time frame for women who have had bariatric surgery, closer surveillance of maternal weight and nutritional status as well as serial monitoring of fetal growth will likely be beneficial. It is important to determine the type of bariatric surgery, restrictive (banding) or bypass (Roux-en-Y), because they may present different challenges during the pregnancy and at delivery.

Several groups have recommended a broad evaluation for micronutrient deficiencies at the beginning of pregnancy for women who have had bariatric surgery. If a deficit is detected, then treatment and monitoring should ensue. However, there is only “expert” opinion to guide which tests to run, how to supplement and what, if any, clinical complication might occur owing to a deficiency in these micronutrients.[29]  If no deficiencies are found, then monitoring every trimester should be considered.[4]  

Obstetric care providers should be aware of bariatric-related operative complications during pregnancy, such as anastomotic leaks or bowel obstructions. Medication dosages may also need to be altered, such as avoidance of extended-release preparations. Alternatives to screen for gestational diabetes should be considered for patients who have had malabsorptive procedures such as a Roux-en-Y gastric bypass, owing to the dumping syndrome that can occur. For example, these patients could check fasting and postprandial blood glucose levels for one week. Another option is to check A1c, and if the value is 6.5% or greater, assume overt diabetes. If the A1c value is normal, then screen with home blood glucose monitoring.

Fetal weight gain is also problematic during pregnancy for an obese patient. Her comorbidities may make her more likely to have placental dysfunction, with resulting intrauterine fetal growth restriction (IUGR). However, her insulin resistance and the tendency for obese women to gain excessive weight place the fetus at risk for macrosomia. Because clinical assessment of fetal size by abdominal palpation and fundal height measurement is more challenging, ultrasound assessment of fetal growth every 4-6 weeks is reasonable for most obese pregnant women. In the setting of severe obesity (BMI of 40 kg/m2 or greater), growth scans should be done at least every 4 weeks to identify abnormalities in growth pattern. In the setting of concerning growth, they can be performed every 3 weeks with interventions for IUGR as indicated.

Timing of delivery

Obesity increases the risk of medically indicated preterm delivery, primarily because of obesity-related maternal disorders such as diabetes or preeclampsia. In a systematic review, overweight and obese women were at increased risk of induced preterm birth compared with women of normal BMI (relative risk [RR], 1.30; 95% CI, 1.23-1.37, five studies) and the risk increased with increasing weight.[30]

Whether obesity increases the risk of spontaneous preterm birth is less clear. There is an association between obesity and post-term pregnancy.[31, 32]  The mechanism has not been determined. One hypothesis is that hormonal changes associated with obesity may interfere with the hormonal changes that initiate the onset of parturition. Another hypothesis is that gestational age calculated from the last menstrual period overestimates true fetal age because obese women tend to be oligo-ovulatory.

Even though stillbirth rates are higher in obese gravidas, there is no definitive evidence showing a clear improvement in pregnancy outcomes with antepartum surveillance. Based on consensus and expert opinion, a recommendation has been made that for women with a pre-pregnancy BMI of 35.0-39.9 kg/m2, weekly antenatal fetal surveillance may be considered beginning by 37.0 weeks of gestation. For women with a pre-pregnant BMI of 40 kg/m2 or greater, this surveillance may be considered starting at 34.0 weeks of gestation.[19]

A controversial area is timing of delivery. Induction of the obese patient by the estimated date of delivery is reasonable and does not appear to increase the cesarean delivery rate.[33]  Obese women are at increased risk for labor induction anyway because of their increased risk of pregnancy complications. They are also at increased risk for induction failure. A study looking at the effect of maternal obesity on the rate of failed induction of labor found that increasing obesity class is associated with an increased risk of failed induction of labor, from 13% in normal-weight women to 29% in women with class III obesity. Fetal weight and parity also play an important role in the prediction of induction outcome. Limitations of the data in this study prevented further analysis of the exact reasons for the dramatically increased rates of failed induction in obese women compared with normal-weight women.[34]

Another area of controversy is the best mode of delivery, especially in the setting of class III obesity or greater. One retrospective cohort study looked at 661 women with a BMI of >40 kg/m2 who delivered between 37 and 41 weeks via planned cesarean section or induction of labor (regardless of eventual delivery route) and were not experiencing spontaneous labor. A composite of maternal morbidity was the primary outcome, and a composite of neonatal morbidity was the secondary outcome. Findings showed that in the setting of women with class III obesity, a planned cesarean delivery does not appear to reduce overall maternal and neonatal morbidity compared with induction.[35]

The data on a trial of labor after a cesarean section are mixed. Thus, a decision regarding the attempt of such a trial depends on patient preference, indications for the primary cesarean section, and other obstetric issues using a shared medical decision-making approach.

External cephalic version is not contraindicated in obese women for fetal malpresentation. However, it becomes increasing difficult with increasing maternal weight, especially in a case of more central distribution. Some studies have found that obesity was associated with a higher failure rate. It may be easier to attempt a version with the aid of spinal anesthesia to allow deeper palpation.[36, 37]  Timing of versions is also challenging because the comorbidity of diabetes mellitus with polyhydramnios may contribute to a fetus having an unstable lie and result in the fetus converting back to breech if done too soon. 

Intrapartum treatment will be altered for the obese gravida, especially the morbidly obese (BMI of >40 kg/m2). The labor and delivery unit will need special gowns, beds, doorways, and stretchers. Given the increased probability of operative interventions in obese patients, operating tables, lifting equipment, disposable pannus retractors, and surgical instruments that are appropriate for care of obese women need to be readily available. Most of the issues covered in the American College of Obstetricians and Gynecologists (ACOG) committee opinion on gynecologic surgery in the obese woman are pertinent to the obese obstetric patient.[38]  Fetal monitoring with external Doppler ultrasound can be difficult, and placement of an internal fetal scalp electrode and intrauterine pressure catheter may be useful.

To help ensure that the entire unit is aware of patients who have class III or higher obesity so that they can be prepared to modify management or address the challenges in an emergency with these patients, the “labor board” could include a column with information regarding obesity. In this way, the anesthesia service and others on the unit can be made aware of the possible need for assistance with a complicated case.

Anesthesia consultation early in labor is encouraged, especially with patients who have BMIs of 40 kg/m2 or higher, as there are many challenges posed by maternal obesity. Even if a patient does not plan on having a laboring epidural, anesthesia involvement in patients with a higher BMI is common; thus, early brief consultation can help everyone be prepared for emergent needs.

Epidural or spinal anesthesia may be technically difficult to place owing to body habitus and loss of landmarks. Early placement of an epidural catheter increases the likelihood of being able to utilize regional anesthesia successfully in the setting of an urgent cesarean section. General anesthesia could be problematic because of difficulties with endotracheal intubation due to excessive tissue and edema, patient positioning, or a heavy pannus compromising ventilation. The necessary equipment will need to be available (blood pressure cuffs, venous access, fiberoptics for intubation). Patients with OSA are at risk for additional challenges for both regional and general anesthesia.[37]

Increasing BMI is associated with longer incision-to-delivery time, which may increase neonatal morbidity, particularly in emergency situations.[39]  It is important not to wait until the last moment to transport the patient to the operating room, place an epidural catheter, etc, especially in the setting of morbid obesity and severe morbid obesity. The time and personnel it takes to move an obese patient (especially someone with a BMI of 40 kg/m2 or higher) to the operating room and position her can be far greater than for a non-obese individual. This factor needs to be considered as a provider evaluates fetal status and labor progression.

The median duration of labor from 4 to 10 cm is significantly longer for both overweight and obese women compared with normal-weight women (7.5, 7.9, and 6.2 hours, respectively).[40]  This must be considered prior to diagnosing a failed induction or arrest of stage 1. Duration of the second stage of labor does not appear to be affected by increasing BMI.[41]

Studies have shown that a trial of labor after cesarean section is less likely to be successful in increasingly obese women. Operative vaginal delivery is also more likely if a woman is obese (control, 10.5%; obese, 8.5%; and morbidly obese, 11.1%).[42]

Macrosomia or birth weight >4000 g is more common in the infants of obese women and is a risk factor for shoulder dystocia. For moderate obesity, the shoulder dystocia OR is 1.51 (95% CI, 1.32-1.74) compared with non-obese women.[23]  

For women with moderate obesity, the risk of postpartum hemorrhage is higher (OR, 1.12; 95% CI, 1.02-1.22) compared with non-obese women.[23]  Given the increased risk of hemorrhage and the increased difficulty in acquiring intravenous (IV) access as BMI increases, a provider should evaluate an obese patient on the labor and delivery unit for a large bore IV (16 gauge) or placement of 2 IVs that are secured. In the severely morbidly obese patient, a longer than typical angiocatheter or central line placement may be necessary to ensure adequate IV access in the setting of a massive hemorrhage. Hemoglobin/hematocrit should be noted on admission to the labor and delivery unit, and all labor stages should be managed to minimize hemorrhage risks.

Numerous studies report an increased risk of cesarean delivery among overweight and obese women compared with normal-weight women.[43] The optimal skin incision for primary cesarean delivery in patients with a BMI greater than 35 kg/m2 has not been determined.[19]  Much of this depends on the distribution of the weight and the height of the patient. On admission to the labor and delivery unit, consideration should be given to the location of a surgical incision should a cesarean section be necessary in all patients who are morbidly obese. A supra-umbilical incision may be preferred if the patient has a large pannus. After adjusting for confounding factors, a vertical incision is associated with a significantly lower risk of wound complications.

An appropriate dose of prophylactic antibiotics should be administered based on maternal weight. Some recommendations based on general surgical procedures would suggest a 2-g prophylactic cefazolin dose for women who weigh more than 80 kg (175 lb), with an increase to 3 g for those who weight more than 120 kg (265 lb).[44]  Few studies have specifically addressed the question of weight-based dosing for antibiotic prophylaxis at the time of cesarean delivery. These have had mixed results. An additional suggested strategy is a second dose of antibiotics 4 hours after the first.

The obese gravida is at higher risk for postpartum infection regardless of mode of delivery, including wound, episiotomy, and endometritis. Various strategies have been tried to minimize these risks. Good glucose control, strict aseptic technique, and appropriate antibiotic use have helped to decrease the infection rate.[45]  Prior to a cesarean section, skin cleansing with an alcohol-based solution should be performed if no contraindications exist. Vaginal cleansing prior to cesarean section in laboring patients or those with ruptured membranes may be considered. Routine use of subcutaneous drains, delayed skin closure at cesarean section, or use of incisional wound vacuum-assisted closure (VAC) have not demonstrated a decreased infection rate. In the setting of a BMI of 50 kg/m2 or higher, more than 30% of women had a wound infection, which was typically diagnosed at 6-12 days post-surgery.[46, 47]

In one review, the ORs of postpartum venous thromboembolism in women with class I, II, and III obesity were 2.5, 2.9, and 4.6, respectively, compared with women whose BMI was normal.[48]  Pharmacologic thromboprophylaxis should be considered in addition to pneumatic compression devices. The use of pharmacologic thromboprophylaxis and the duration of postpartum prophylaxis depend on several patient-specific factors. For instance, patients with preeclampsia, fetal growth restriction, infection, and emergency cesarean delivery are at increased risk for venous thromboembolism.[49]

Any of these risks in the setting of BMI of 40 or higher should prompt a consideration for thromboprophylaxis postpartum.[50]  Although in the past the dosing of low molecular weight (LMW) heparin was based on BMI categories (40 mg of enoxaparin bid if the BMI is 40-59.9 kg/m2 and 60 mg if the BMI is 60 kg/m2 or greater), more recent studies show that weight-based dosing may be preferable (0.5 mg/kg enoxaparin bid).

Obese women are prone to difficulty with lactation. Consultation with a lactation specialist while in the hospital and access after discharge are helpful.[51]

Close follow-up postpartum for the first 6 weeks is often indicated, especially in the setting of operative delivery or intrapartum comorbidities.  Attention needs to be given to the maternal comorbidities that were present at the onset of the pregnancy or that developed during the pregnancy to see if they persist or resolve. Ongoing primary care to help with the management of persistent morbidities such as diabetes, hypertension, and fatty liver, as well as weight loss, is important.

Importantly, children of obese women have a predisposition to obesity later in their life. Postpartum women should be supported in their efforts to lose gestational weight gain, avoid postpartum weight gain, and achieve a healthy/healthier BMI. A woman with a BMI of 35 kg/m2 or greater may not feel it is possible to achieve a BMI of < 30 kg/m2.  Telling a patient that the loss of 10% of her body weight has significant health benefits can be helpful as it may be seen as an achievable goal by the patient. Interpregnancy weight gain or interpregnancy weight loss can affect risks in a subsequent pregnancy.

All women with obesity should be provided with or referred to behavioral counseling interventions focused on improving diet and encouraging exercise in order to achieve a healthier weight before another pregnancy, as well as to improve their own health. Women with higher BMIs may also be referred to a bariatric surgery team for evaluation.

Table. A Series of Considerations for the Management of the Obese Patient (Open Table in a new window)

The goals of pharmacotherapy are to reduce morbidity and prevent complications.

Class Summary

Therapy must cover all likely pathogens in the context of this clinical setting. Prophylactic antibiotics should be administered based on maternal weight.

Cefazolin

First-generation semisynthetic cephalosporin that arrests bacterial cell wall synthesis, inhibiting bacterial growth. Based on general surgical procedures, the suggested recommended dose is a 2-g prophylactic dose for women who weigh >80 kg (175 lb), with an increase to 3 g for those who weight >120 kg (265 lb). Another suggested option is to repeat the dose in 4 hours.