Maternal factors associated with fetal macrosomia

Fetal macrosomia is an obstetric condition that can lead to serious perinatal complications. According to the definition from the American College of Obstetrics and Gynecology (ACOG), excessive fetal growth is referred to as large for gestational age (LGA) or macrosomia.¹ LGA is typically representative of a birth weight ≥ the 90th percentile for a given gestational age.¹ In the Asian population, fetal macrosomia is usually defined as an estimated fetal weight or birth weight >4000 g.² Women with macrosomia are more likely to have cesarean deliveries (CD) and other obstetric and perinatal complications. As a birth weight increases, the risk of shoulder dystocia, birth-related trauma, and long-term birth-related injuries is increased. To raise awareness about this critical issue and prevent maternal and fetal adverse outcomes resulting from fetal macrosomia, we highlight a recent article published in the 2023 Journal of the Chinese Medical Association (JCMA), entitled “Association between maternal factors and fetal macrosomia in full-term singleton births,” which attempted to identify maternal factors related to fetal macrosomia in a Taiwanese population.³

Chen et al³ retrospectively analyzed data from 4262 full-term singleton infants delivered at Taipei Veterans General Hospital between January 2013 and June 2016. They found that the prevalence of macrosomia was 1.8% and the following risk factors, including gestational diabetes mellitus (GDM), 6-month gestational weight gain (6m GWG), and maternal body mass index (BMI) were significantly associated with neonatal macrosomia in term singleton births. The odds ratio (OR) of macrosomia was 3.1 in neonates born to mothers with a 6m GWG of ≥15 kg, 6.3 in those born to mothers with GDM, and 4.1 in those born to mothers with a BMI of ≥30 kg/m², respectively.³ Therefore, the authors suggested the importance of maternal counseling for weight management before and during pregnancy. The study is noteworthy and worthy of further discussion.

First, we have noticed that taller maternal height (≥164 cm) is associated with an increased risk of macrosomia (p = 0.008) in multivariate analysis, suggesting that this risk factor is independent after adjusting other cofounders, such as BMI. Additionally, maternal height is inversely correlated with maternal BMI.⁴ According to this study’s results, should taller mothers be aware of the risk of macrosomia? It is interesting to know why the authors have neglected the aforementioned finding and no further discussion or evaluation is provided.

Second, the authors enrolled all singleton pregnancies delivered at a gestational age of ≥37 weeks in their analysis and defined these newborns were “full-term,” which is at high risk or possibility to misuse this description.^5,6 The proper terminology is “term” pregnancies, referring to pregnancies that have reached 37 to 42 weeks of gestation, in place of the original form “full-term” which may be limited to gestational weeks between 39 + 0 weeks and 40 + 6 weeks.⁷

Third, since the current study aimed to identify the risk factors of neonatal macrosomia, neonates born with low birth weight (<2500 g) should have been excluded from the data analysis to ensure accurate statistical results. Therefore, it would be beneficial not to separate the enrolled patients into 3 groups so that the essential baseline characteristics of macrocosmic vs normal groups can be compared directly. It is also unclear why the authors included patients with preeclampsia in the analysis, as placental dysfunction, a core etiology for the development of preeclampsia, could drastically impact fetal growth and lead to intrauterine growth restriction (IUGR), resulting in significant confounding in the data analysis.

It should be noted that both one- and two-step approaches were used to screen for GDM during the data collection. Despite more diagnoses (higher prevalence) of GDM with the one-step approach than with the two-step approach, there were no significant between-group differences in the risks of the primary outcomes relating to perinatal and maternal complications, according to a recent randomized controlled study.⁸ However, the authors stated that the GDM diagnosis was based on the one-step 75 g OGTT might be unlikely. Furthermore, the authors stated that maternal complications in patients with macrosomia group include a high risk of hemorrhage during delivery and uterine rupture.^9–11 However, this statement is not supported by the data presented in the study. It is commonly known that CD has a higher predicted surgical blood loss than normal spontaneous vaginal delivery, which is why the definition of post-partum hemorrhage (PPH) differs between the two delivery methods.¹¹ There is a direct causal relationship between a higher CD rate and increased blood loss in patients with fetal macrosomia. Additionally, this study does not present any data regarding the risk of uterine rupture. It is unclear whether the authors discovered these findings elsewhere.

Although some arguments might require clarification, the efforts made by the authors to identify risk factors for fetal macrosomia are greatly appreciated. Further studies focusing on increasing the accuracy of estimating fetal weight and preventing the adverse outcome of neonatal macrosomia remain a priority task for obstetricians.^12–14 This could lead to a decrease in the rate of planned cesarean sections and inappropriate labor inductions.^5,6,15 Efforts should also include close counseling and follow-up of women throughout pregnancy to provide advice on avoiding weight gain that exceeds guidelines for gestational weight gain. This is of paramount importance.

ACKNOWLEDGMENTS

This article was supported by grants from the Taiwan Ministry of Science and Technology, Executive Yuan, Taiwan (MOST 110-2314-B-075-016-MY3 and MOST 111-2314-B-075-045), and Taipei Veterans General Hospital (V112C-154 and V112D64-001-MY2-1).

The authors appreciate the support from Female Cancer Foundation, Taipei, Taiwan.