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Should pregnancies be induced for impending macrosomia?
Comment
Should pregnancies be induced for impending macrosomia? specified macrosomic birthweight and compared this intervention with expectant management to a greater gestational age and greater birthweight, women undergoing induction of labour had lower rates of caesarean delivery; but fetal birth injury did not differ between groups. Part of the problem of such studies is that induction was not used until fetal macrosomia was already suspected. This has led to a practice of inducing women whose fetuses have so-called impending macrosomia—an approach that would make sense if a good way to identify such fetuses existed, but lacking evidence-based support. In The Lancet, Michel Boulvain and colleagues7 report a well powered, multicentre, randomised controlled trial of induction of labour versus expectant management for women at 37–39 weeks of gestation, with fetuses whose weights exceeded the 95th percentile or above for estimated weight. That is, the fetuses were not suspected of being macrosomic, but instead of having impending macrosomia. The primary outcome was a composite of clinically significant shoulder dystocia, fracture of the clavicle, brachial plexus injury, intracranial haemorrhage or death. In the induction of labour group, 366 (90%) of 407 women were induced, whereas only 116 (28%) of 411 women were induced in the expectant management group. The investigators showed that neonates born to women in the induction of labour group had a lower risk of the primary outcome than did those born to women in the expectant management group (n=eight vs n=25; relative
www.thelancet.com Published online April 9, 2015 http://dx.doi.org/10.1016/S0140-6736(14)62302-3
Published Online April 9, 2015 http://dx.doi.org/10.1016/ S0140-6736(14)62302-3 See Online/Articles http://dx.doi.org/10.1016/ S0140-6736(14)61904-8
Ian Hooton/Science Photo Library
Fetal macrosomia (usually defined as an estimated fetal weight or birthweight >4000 g or ≥4500 g) is associated with various perinatal complications. Irrespective of which weight threshold is used, macrosomic fetuses have higher rates of shoulder dystocia and subsequent birth trauma than do non-macrosomic fetuses.1 Additionally, women with macrosomic fetuses are at high risk of caesarean deliveries and other complications, such as postpartum haemorrhage and venous thromboembolism.2 One of the strongest risk factors for fetal macrosomia is prepregnancy obesity, but because preconception consultations are rarely done for most obese women, the best way to prevent fetal macrosomia is with close counselling and follow-up of women throughout pregnancy to provide advice on avoiding weight gain in excess of guidelines for gestational weight gain from the US Institute of Medicine.3 However, despite doctors’ best efforts, macrosomic fetuses will still develop in term pregnancies. One approach to the safe delivery of macrosomic or largefor-gestational-age fetuses has been to induce labour before the fetus crosses a weight threshold of clinical concern. Yet findings from retrospective studies4,5 have shown no benefit of induction of labour for fetal macrosomia compared with spontaneous labour. In fact, one study4 reported increased rates of caesarean deliveries with labour induction, with no reductions in birth injury. Similarly, a randomised controlled study5 that examined the effect of induction of labour versus expectant management, in women without diabetes but with suspected fetal macrosomia, reported no statistically significant difference in rates of caesarean delivery (19·4% for the induction group and 21·6% for the expectant management group) or shoulder dystocia. What is the difference between retrospective studies and randomised trials that compare induction of labour? In the clinical environment, doctors and patients are faced with a choice between induction of labour and expectant management. Expectant management includes spontaneous labour, but can also lead to the development of pregnancy complications and increased fetal growth. Hence, most observational studies of induction of labour have used spontaneous labour instead of expectant management. However, in a study6 that assessed induction of labour at a
1
Comment
risk 0·32, 95% CI 0·15–0·71) and a lower risk of any shoulder dystocia (15 vs 32; 0·47, 0·26–0·86). Neonates in the induction group had a lower mean birthweight than did those in the expectant management group (3831 g [SD 324] vs 4118 g [392]), and a significantly higher proportion needed phototherapy to treat hyperbilirubinaemia (45 vs 27, p=0·03). However, neither transient tachypnoea of the newborn nor respiratory distress syndrome differed between the groups. Additionally, the difference in risk of caesarean delivery was not statistically significant, although the absolute rate was lower for the women who were assigned to induction of labour than for those assigned to expectant management. In view of the existing focus on prevention of nonmedically indicated induction of labour, Boulvain and colleagues’ trial7 presents timely evidence of the potential benefit of induction of labour for prevention of adverse outcomes. A previous trial8 that focused on prevention of caesarean deliveries by induction of labour in at-risk women reported that women who were induced had a better neonatal adverse outcome index (1·4 vs 8·6, p=0·03) compared with those managed expectantly. As in Boulvain and colleagues’ trial, many women in the previous trial8 were induced before 39 weeks of gestation. Notably, in one of the most cited studies9 that led to a push towards reduction of induced deliveries before 39 weeks of gestation, the population was composed of women who had a caesarean delivery, whose neonates have increased rates of transient tachypnoea of the newborn. Ultimately, the fundamental question is of the number needed to prevent a rare outcome; what are the trade-offs between the benefits and risks of intervention versus expectant management? Are the outcomes worth the induction of 25 women to prevent one case of shoulder dystocia? Is treatment of an additional neonate with phototherapy worth the prevention of a case of shoulder dystocia? The findings of the accompanying study raise these underlying clinical questions. Although Boulvain and colleagues’ study7 is the first to show a reduction of shoulder dystocia with induction of labour in the setting of impending macrosomia, with existing guidelines for gestational age, expansion of this practice would need to be restricted to 39 weeks
2
of gestation and beyond to avoid any increase in neonatal complications of prematurity.10 However, to wait until 39 weeks of gestation might also decrease the benefit for shoulder dystocia. Thus, these findings place clinicians and their patients in a difficult position— is intervention better than expectant management for impending macrosomia, and at what gestational age should it be done? Findings from the present study provide evidence to counsel patients, but do not establish what is best practice. How these findings will be incorporated into worldwide guidelines for care will be very interesting. Clinicians will need to consider carefully how estimated fetal weight is measured and the effect of variations in the practice of induction of labour. Before guidelines are changed, clinicians and patients will need to engage in shared medical decision making based on a common theme in obstetrics— imperfect, but intriguing, new evidence. Aaron B Caughey Department of Obstetrics and Gynecology, Oregon Health and Science University, Portland, OR 97239, USA [email protected] I declare no competing interests. 1
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Esakoff TF, Cheng YW, Sparks TN, Caughey AB. The association between birthweight 4000 g or greater and perinatal outcomes in patients with and without gestational diabetes mellitus. Am J Obstet Gynecol 2009; 200: 672.e1–4. Stotland NE, Hopkins LM, Caughey AB. Gestational weight gain, macrosomia, and the risk of cesarean birth in nondiabetic nulliparas. Obstet Gynecol 2004; 104: 671–77. Swank ML, Caughey AB, Farinelli CK, et al. The impact of change in pregnancy body mass index on macrosomia. Obesity (Silver Spring) 2014; 22: 1997–2002. Combs CA, Singh NB, Khoury JC. Elective induction versus spontaneous labor after sonographic diagnosis of fetal macrosomia. Obstet Gynecol 1993; 81: 492–96. Gonen O, Rosen DJ, Dolfin Z, Tepper R, Markov S, Fejgin MD. Induction of labor versus expectant management in macrosomia: a randomized study. Obstet Gynecol 1997; 89: 913–17. Cheng YW, Sparks TN, Laros, RK, Nicholson JM, Caughey AB. Impending macrosomia: will induction of labour modify the risk of cesarean delivery? BJOG 2012; 119: 402–09. Boulvain M, Senat M-V, Perrotin F, et al, for the Groupe de Recherche en Obstétrique et Gynécologie (GROG). Induction of labour versus expectant management for large-for-date fetuses: a randomised controlled trial. Lancet 2015; published online April 9. http://dx.doi.org/10.1016/S01406736(14)61904-8. Nicholson JM, Parry S, Caughey AB, Rosen S, Keen A, Macones GA. The impact of the active management of risk in pregnancy at term on birth outcomes: a randomized clinical trial. Am J Obstet Gynecol 2008; 198: 511.e1–15. Tita AT, Landon MB, Spong CY, et al. Timing of elective repeat cesarean delivery at term and neonatal outcomes. N Engl J Med 2009; 360: 111–20. American College of Obstetricians and Gynecologists. ACOG committee opinion no. 561: nonmedically indicated early-term deliveries. Obstet Gynecol 2013; 121: 911–15.
www.thelancet.com Published online April 9, 2015 http://dx.doi.org/10.1016/S0140-6736(14)62302-3
Should pregnancies be induced for impending macrosomia? specified macrosomic birthweight and compared this intervention with expectant management to a greater gestational age and greater birthweight, women undergoing induction of labour had lower rates of caesarean delivery; but fetal birth injury did not differ between groups. Part of the problem of such studies is that induction was not used until fetal macrosomia was already suspected. This has led to a practice of inducing women whose fetuses have so-called impending macrosomia—an approach that would make sense if a good way to identify such fetuses existed, but lacking evidence-based support. In The Lancet, Michel Boulvain and colleagues7 report a well powered, multicentre, randomised controlled trial of induction of labour versus expectant management for women at 37–39 weeks of gestation, with fetuses whose weights exceeded the 95th percentile or above for estimated weight. That is, the fetuses were not suspected of being macrosomic, but instead of having impending macrosomia. The primary outcome was a composite of clinically significant shoulder dystocia, fracture of the clavicle, brachial plexus injury, intracranial haemorrhage or death. In the induction of labour group, 366 (90%) of 407 women were induced, whereas only 116 (28%) of 411 women were induced in the expectant management group. The investigators showed that neonates born to women in the induction of labour group had a lower risk of the primary outcome than did those born to women in the expectant management group (n=eight vs n=25; relative
www.thelancet.com Published online April 9, 2015 http://dx.doi.org/10.1016/S0140-6736(14)62302-3
Published Online April 9, 2015 http://dx.doi.org/10.1016/ S0140-6736(14)62302-3 See Online/Articles http://dx.doi.org/10.1016/ S0140-6736(14)61904-8
Ian Hooton/Science Photo Library
Fetal macrosomia (usually defined as an estimated fetal weight or birthweight >4000 g or ≥4500 g) is associated with various perinatal complications. Irrespective of which weight threshold is used, macrosomic fetuses have higher rates of shoulder dystocia and subsequent birth trauma than do non-macrosomic fetuses.1 Additionally, women with macrosomic fetuses are at high risk of caesarean deliveries and other complications, such as postpartum haemorrhage and venous thromboembolism.2 One of the strongest risk factors for fetal macrosomia is prepregnancy obesity, but because preconception consultations are rarely done for most obese women, the best way to prevent fetal macrosomia is with close counselling and follow-up of women throughout pregnancy to provide advice on avoiding weight gain in excess of guidelines for gestational weight gain from the US Institute of Medicine.3 However, despite doctors’ best efforts, macrosomic fetuses will still develop in term pregnancies. One approach to the safe delivery of macrosomic or largefor-gestational-age fetuses has been to induce labour before the fetus crosses a weight threshold of clinical concern. Yet findings from retrospective studies4,5 have shown no benefit of induction of labour for fetal macrosomia compared with spontaneous labour. In fact, one study4 reported increased rates of caesarean deliveries with labour induction, with no reductions in birth injury. Similarly, a randomised controlled study5 that examined the effect of induction of labour versus expectant management, in women without diabetes but with suspected fetal macrosomia, reported no statistically significant difference in rates of caesarean delivery (19·4% for the induction group and 21·6% for the expectant management group) or shoulder dystocia. What is the difference between retrospective studies and randomised trials that compare induction of labour? In the clinical environment, doctors and patients are faced with a choice between induction of labour and expectant management. Expectant management includes spontaneous labour, but can also lead to the development of pregnancy complications and increased fetal growth. Hence, most observational studies of induction of labour have used spontaneous labour instead of expectant management. However, in a study6 that assessed induction of labour at a
1
Comment
risk 0·32, 95% CI 0·15–0·71) and a lower risk of any shoulder dystocia (15 vs 32; 0·47, 0·26–0·86). Neonates in the induction group had a lower mean birthweight than did those in the expectant management group (3831 g [SD 324] vs 4118 g [392]), and a significantly higher proportion needed phototherapy to treat hyperbilirubinaemia (45 vs 27, p=0·03). However, neither transient tachypnoea of the newborn nor respiratory distress syndrome differed between the groups. Additionally, the difference in risk of caesarean delivery was not statistically significant, although the absolute rate was lower for the women who were assigned to induction of labour than for those assigned to expectant management. In view of the existing focus on prevention of nonmedically indicated induction of labour, Boulvain and colleagues’ trial7 presents timely evidence of the potential benefit of induction of labour for prevention of adverse outcomes. A previous trial8 that focused on prevention of caesarean deliveries by induction of labour in at-risk women reported that women who were induced had a better neonatal adverse outcome index (1·4 vs 8·6, p=0·03) compared with those managed expectantly. As in Boulvain and colleagues’ trial, many women in the previous trial8 were induced before 39 weeks of gestation. Notably, in one of the most cited studies9 that led to a push towards reduction of induced deliveries before 39 weeks of gestation, the population was composed of women who had a caesarean delivery, whose neonates have increased rates of transient tachypnoea of the newborn. Ultimately, the fundamental question is of the number needed to prevent a rare outcome; what are the trade-offs between the benefits and risks of intervention versus expectant management? Are the outcomes worth the induction of 25 women to prevent one case of shoulder dystocia? Is treatment of an additional neonate with phototherapy worth the prevention of a case of shoulder dystocia? The findings of the accompanying study raise these underlying clinical questions. Although Boulvain and colleagues’ study7 is the first to show a reduction of shoulder dystocia with induction of labour in the setting of impending macrosomia, with existing guidelines for gestational age, expansion of this practice would need to be restricted to 39 weeks
2
of gestation and beyond to avoid any increase in neonatal complications of prematurity.10 However, to wait until 39 weeks of gestation might also decrease the benefit for shoulder dystocia. Thus, these findings place clinicians and their patients in a difficult position— is intervention better than expectant management for impending macrosomia, and at what gestational age should it be done? Findings from the present study provide evidence to counsel patients, but do not establish what is best practice. How these findings will be incorporated into worldwide guidelines for care will be very interesting. Clinicians will need to consider carefully how estimated fetal weight is measured and the effect of variations in the practice of induction of labour. Before guidelines are changed, clinicians and patients will need to engage in shared medical decision making based on a common theme in obstetrics— imperfect, but intriguing, new evidence. Aaron B Caughey Department of Obstetrics and Gynecology, Oregon Health and Science University, Portland, OR 97239, USA [email protected] I declare no competing interests. 1
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5
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9 10
Esakoff TF, Cheng YW, Sparks TN, Caughey AB. The association between birthweight 4000 g or greater and perinatal outcomes in patients with and without gestational diabetes mellitus. Am J Obstet Gynecol 2009; 200: 672.e1–4. Stotland NE, Hopkins LM, Caughey AB. Gestational weight gain, macrosomia, and the risk of cesarean birth in nondiabetic nulliparas. Obstet Gynecol 2004; 104: 671–77. Swank ML, Caughey AB, Farinelli CK, et al. The impact of change in pregnancy body mass index on macrosomia. Obesity (Silver Spring) 2014; 22: 1997–2002. Combs CA, Singh NB, Khoury JC. Elective induction versus spontaneous labor after sonographic diagnosis of fetal macrosomia. Obstet Gynecol 1993; 81: 492–96. Gonen O, Rosen DJ, Dolfin Z, Tepper R, Markov S, Fejgin MD. Induction of labor versus expectant management in macrosomia: a randomized study. Obstet Gynecol 1997; 89: 913–17. Cheng YW, Sparks TN, Laros, RK, Nicholson JM, Caughey AB. Impending macrosomia: will induction of labour modify the risk of cesarean delivery? BJOG 2012; 119: 402–09. Boulvain M, Senat M-V, Perrotin F, et al, for the Groupe de Recherche en Obstétrique et Gynécologie (GROG). Induction of labour versus expectant management for large-for-date fetuses: a randomised controlled trial. Lancet 2015; published online April 9. http://dx.doi.org/10.1016/S01406736(14)61904-8. Nicholson JM, Parry S, Caughey AB, Rosen S, Keen A, Macones GA. The impact of the active management of risk in pregnancy at term on birth outcomes: a randomized clinical trial. Am J Obstet Gynecol 2008; 198: 511.e1–15. Tita AT, Landon MB, Spong CY, et al. Timing of elective repeat cesarean delivery at term and neonatal outcomes. N Engl J Med 2009; 360: 111–20. American College of Obstetricians and Gynecologists. ACOG committee opinion no. 561: nonmedically indicated early-term deliveries. Obstet Gynecol 2013; 121: 911–15.
www.thelancet.com Published online April 9, 2015 http://dx.doi.org/10.1016/S0140-6736(14)62302-3