INTERGROWTH-21st compared with GROW customized centiles in the detection of adverse perinatal outcomes at term

Abstract

Background: INTERGROWTH-21st charts provide standards for infants born under optimal pregnancy conditions. However, their validity in a general obstetric population is unclear. We aimed to identify whether INTERGROWTH-21st charts, compared with gestation related optimal weight (GROW) charts customized on maternal height, weight, and parity, better identified the at-risk infant.

Methods: We performed a retrospective cohort analysis of all term women who gave birth at a single tertiary obstetric center during the period 1994–2016. Routinely collected maternity data was used for analysis. The primary outcome was an Apgar score <7 at 5 min. Secondary outcomes included Apgar score <5 at 5 min, stillbirth or admission to the neonatal intensive care unit (NICU). Populations of newborns were identified as SGA by: (a) INTERGROWTH-21st <10th centile (SGA_IG10th); (b) INTERGROWTH-21st z-score < −1 (SGA_IGzscore); and (c) GROW customized charts <10th (SGA_cust). The subgroups identified by only one chart were also specifically examined. Each SGA group was compared to infants appropriate for gestational age (AGA) on all charts (non-SGA).

Results: Data for 71,487 births were available for analysis after exclusion of women with missing height or weight data. Only 3280 (4.6%) newborns were considered SGA_IG10th, with 5878 (8.2%) SGA_IGzscore and 7599 (10.6%) SGA_cust. INTERGROWTH-21st identified only 110 additional infants (0.15%) that were not identified by customized charts; none of these experienced any adverse outcomes. Customized centiles identified a further 4429 (6.2%) SGA infants (SGA_cust-only) that were not identified as SGA_IG10th, and who did demonstrate an increased risk of Apgar score <7 (OR 1.33, 95%CI 1.08–3.28) and stillbirth (OR 2.47, 95%CI 1.41–4.44) compared to the non-SGA infant. Significantly more obese women had infants considered SGA_cust (19.3%) than SGA_IG10th (10.0%) or SGA_IGzscore (9.9%).

Conclusions: Amongst our general obstetric study population, the 10th centile of INTERGROWTH-21st identified only 4.6% of infants as SGA and was less likely to identify infants of obese women as SGA. Customized centiles identified almost all SGA-IG infants, including an additional group (SGA_cust-only) at higher risk of stillbirth and adverse outcomes compared with non-SGA infants.

Keywords:

• Customized centiles
• intergrowth
• maternal obesity
• perinatal morbidity
• perinatal mortality

Acknowledgments

We would like to acknowledge the midwives who assisted us in obtaining the data, in particular, Tania Fletcher.

Disclosure statement

No potential conflict of interest was reported by the authors.