Should pregnancies be induced for impending macrosomia?

www.thelancet.com Published online April 9, 2015 http://dx.doi.org/10.1016/S0140-6736(14)62302-3 1 Fetal macrosomia (usually defi ned 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. Additionally, women with macrosomic fetuses are at high risk of caesarean deliveries and other complications, such as postpartum haemorrhage and venous thromboembolism. 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. However, despite doctors’ best eff orts, 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 fi ndings from retrospective studies have shown no benefi t of induction of labour for fetal macrosomia compared with spontaneous labour. In fact, one study reported increased rates of caesarean deliveries with labour induction, with no reductions in birth injury. Similarly, a randomised controlled study that examined the eff ect of induction of labour versus expectant management, in women without diabetes but with suspected fetal macrosomia, reported no statistically signifi cant diff erence 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 diff erence 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 study that assessed induction of labour at a specifi ed 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 diff er 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 colleagues 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 signifi cant 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 Should pregnancies be induced for impending macrosomia?