An Outcome-based Approach for the Creation of Fetal Growth Standards: Do Singletons and Twins Need Separate Standards?

Abstract

Contemporary fetal growth standards are created by using theoretical properties (percentiles) of birth weight (for gestational age) distributions. The authors used a clinically relevant, outcome-based methodology to determine if separate fetal growth standards are required for singletons and twins. All singleton and twin livebirths between 36 and 42 weeks’ gestation in the United States (1995–2002) were included, after exclusions for missing information and other factors (n = 17,811,922). A birth weight range was identified, at each gestational age, over which serious neonatal morbidity and neonatal mortality rates were lowest. Among singleton males at 40 weeks, serious neonatal morbidity/mortality rates were lowest between 3,012 g (95% confidence interval (CI): 3,008, 3,018) and 3,978 g (95% CI: 3,976, 3,980). The low end of this optimal birth weight range for females was 37 g (95% CI: 21, 53) less. The low optimal birth weight was 152 g (95% CI: 121, 183) less for twins compared with singletons. No differences were observed in low optimal birth weight by period (1999–2002 vs. 1995–1998), but small differences were observed for maternal education, race, parity, age, and smoking status. Patterns of birth weight-specific serious neonatal morbidity/neonatal mortality support the need for plurality-specific fetal growth standards.

Optimal timing of delivery in pregnancies with pre-existing hypertension

“…Serious neonatal morbidity was defined as a composite outcome which included any of the following: neonatal seizures, 5-minute Apgar score £3 or severe respiratory morbidity (need for assisted ventilation for 30 minutes or more). 12,13 The components of the composite outcome were chosen because each of the events is very strongly associated with death and serious disability in long-term follow-up studies. 14,15 Caesarean delivery following induction of labour was examined as a secondary outcome.…”

Conceptual issues related to the construction of prescriptive standards for the evaluation of postnatal growth of preterm infants

“…The inclusion of populations from different geographical regions is supported by the recent WHO standards that pooled six ethnic groups around the world47 and by the limited racial differences observed in the US 1995–2002 newborn population (23 g 95% CI: 8 to 38 g) between the birth weights of African American and white infants when studying the relationship between low fetal optimal weight and neonatal morbidity and mortality 48. These authors concluded that “because such a small difference may not be clinically relevant and possibly also confounded by uncontrolled factors, (we) do not believe that this study supports separate fetal growth standards by race, educational status, parity, smoking and maternal age” 48.…”

The Effect of Prepregnancy Body Mass Index and Gestational Weight Gain on Birth Weight

“…The National Center for Health Statistics in the United States reported similar findings for the year 1995-2002, using singletons data (Joseph et al, 2009). For centuries, gestational maturity has been understood as important to infant survival.…”

“…Research establishing an association between birth weight and neonatal morbidity/ mortality rates in term livebirth infants is limited. Joseph et al (2009) show the birth weight-specific rates of serious neonatal morbidity and neonatal mortality in 17,554,934 livebirths from perinatal mortality data files of the National Center for Health Statistics for the years 1995-2002. All were singleton livebirths with a clinical estimate of gestation between 36 and 42 weeks born to white or black mothers in the United States (Figure 1).…”