Obesity and pregnancy: implications for maternal and fetal outcomes

Keywords::

• BMI
• cesarean section
• gestational diabetes
• obesity
• preeclampsia
• pregnancy
• ultrasound

Obesity is an excess of adipose tissue to an extent of health impairment and is usually defined as BMI (weight/height²) ≥30 kg/m² [101]. During the past 20 years, obesity has become a worldwide epidemic with an estimate of 200 million men and 300 million women that were obese in 2008 [101]. The WHO estimates that approximately 700 million adults will be obese by 2015 [101].

As the prevalence of obesity is increasing, so is the number of obese women of reproductive age and, consequently, obesity complicates as many as 18.5–38.3% of pregnancies [102]. These pregnancies are at an increased risk of several maternal as well as fetal adverse outcomes.

Gestational hypertension and preeclampsia are 2.5–3.2- and 1.6–3.3-times more common, respectively, among obese women [1,2]. In our recent population-based survey, several factors known to increase the risk of preeclampsia in singletons, such as advanced maternal age, preexisting hypertension and so on, were not significantly associated with preeclampsia in twin pregnancies, which inherently carry a higher risk of hypertensive disorders. On the other hand, the association between high prepregnancy BMI and preeclampsia was highly significant [3]. This emphasizes the important association of obesity with preeclampsia.

The incidence of gestational diabetes is three- to five-times higher in obese women [2,4], and up to one-third of all cases of gestational diabetes are attributable to obesity [5]. Obese women also suffer from pregestational diabetes much more frequently (>7%) than women with a lower BMI (<1%) [6].

The association between maternal obesity and preterm birth remains controversial. Studies have shown increased, unchanged and reduced risk of prematurity in obese mothers [7]. Current evidence suggests that obesity may be associated with induced preterm delivery but not with spontaneous preterm birth [1].

Based on our analysis of over 173,000 deliveries, pregravid obesity increases the risk of preeclampsia, gestational diabetes and preterm birth at <34 weeks in singleton and in twin gestations (unpublished data). The increased risks associated with obesity twin gestations, which are inherently prone to these complications, highlights the importance of prepregnancy BMI on pregnancy outcome.

Fetal complications of maternal obesity have also been described. Fetal macrosomia is 1.5–2-times more likely in obese mothers, and the risk is increased independently of whether gestational diabetes is present or not [1,8]. The risk of stillbirth is also increased two-fold to three-fold in these pregnancies [9]. Additionally, fetal structural anomalies, such as neural tube defects, omphalocele and cardiac defects, are up to three-times more common if the mother is obese [10,11]. The latter is especially significant given the frequent imaging difficulties in obesity. During the FaSTER trial, for example, researchers from some of the world’s finest diagnostic centers were unable to complete the fetal anatomy scan in 40% of obese women [12]. It has also been described that performing accurate nuchal translucency measurements as part of first-trimester screening is more difficult and more time consuming in obese women. Moreover, a positive relationship exists between maternal BMI and fetal nuchal translucency thickness. Larger nuchal translucency in healthy fetuses of obese women may affect screening performance and entails unnecessary anxiety and invasive tests in these patients [13].

Maternal obesity also has an important health repercussions on the fetus that go beyond intrauterine life. Macrosomia leads to obesity in adolescents as well as in adults, thus creating a viscous circle that contributes to the worldwide epidemic increase in obesity [14].

Obesity also frequently complicates delivery. It is associated with monitoring difficulties, a 1.7-fold increased risk of operative vaginal delivery, and two- to three-times increased risk of cesarean section [1]. Cesarean delivery may be further complicated by obesity, such as difficulties with both regional and general anesthesia, problems with optimal incision, increased operating time and blood loss [15], wound infection/breakdown, postpartum endometritis and venous thromboembolism [1,2,15].

Management of obese pregnant women is guided by the clinician’s awareness of potential complications associated with maternal obesity. We need to discuss these complications with patients and explain the limitations of diagnostic procedures related to their body habits. Screening for diabetes is recommended at the first prenatal visit and (if negative) repeated at 24–28 weeks. Obese women need to be screened for prepregnancy hypertension early and for preeclampsia later in pregnancy. Intrapartum and postpartum complications should be anticipated and anesthetists consulted early. Thromboprophylaxis and early ambulation are advocated postoperatively.

It is imperative to discuss the optimal weight gain with obese pregnant patients. According to the 2009 Institute of Medicine guidelines, women with a prepregnancy BMI ≥30 kg/m² should not gain more than 9 kg (20 lbs) during pregnancy [103]. Excessive weight gain is the strongest factor for weight retention after pregnancy and it further increases the risks of prepregnancy obesity in the next conception [16]. Evidence exists that appropriate counseling about weight gain correlates with actual weight gain [17]. Unfortunately, up to one third of women do not receive information at all from any counseling on weight gain [17].

Even with optimal weight gain, however, the risks of prepregnancy obesity are still present. Once an obese woman is pregnant, we should intercept complications early and possibly reduce their impact on maternal and/or fetal health. Hence, the first and ideal goal in managing obesity in pregnancy is prevention. Clinicians should encourage changes in dietary and physical activity patterns that will lead to weight loss before conception. In addition, weight reduction should precede infertility treatment in obese patients. Realistically, however, achieving normal weight before conception is very difficult for obese women. The lifestyle that leads to obesity is often perpetuated by lack of supportive policies in many sectors: agriculture, food processing, transport, marketing, urban planning, education and health services. Given the increasing number of obese young women and the expected adverse consequences of obesity in pregnancy, strategies to prevent obesity should become high priority in our societies.

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.