Circulating SPINT1 in the second trimester is reduced among pregnancies that ends in low birthweight neonates: cohort study of 2006 pregnancies.

Abstract

<h4>Objective</h4>Serine peptidase inhibitor Kunitz- type-1 (SPINT1) is a circulating protein with possibly the strongest association with low birthweight and placental insufficiency yet reported. At 36 weeks' gestation low plasma SPINT1 was strongly linked with birth of a neonate <10^th centile birthweight (p=2.7 × 10^-13; Australian cohort¹) as were levels at 26-34 weeks' gestation (validation cohorts in United Kingdom¹ and Singapore²). Its biomarker performance appeared to consistently outperform circulating placental growth factor¹. Furthermore, it is plausible that placental SPINT1 could be a disease driver of placental insufficiency: it is highly expressed in placenta, low levels are consistently associated with disease and Spint1 deficiency in genetic mouse knockout studies is embryonically lethal (with severe placental abnormalities)³. Demonstrating that low SPINT1 levels from early pregnancy precedes low birthweight would further strengthen the case that it is a disease driver (temporality⁴). Therefore, we examined whether plasma SPINT1 concentrations at 15 and 20 weeks' gestation are associated with neonates with a birthweight <3^rd or <10^th centile.<h4>Study design</h4>We measured SPINT1 concentrations in plasma at 15 and 20 weeks' gestation from the Screening for Pregnancy Endpoints (SCOPE) cohort from New Zealand (see McCowan et al for details⁵). Plasma SPINT1 concentrations were measured by ELISA (Sigma-Aldrich, St Louis, Missouri, USA). We compared levels among pregnancies that ended with a neonate born at either <3^rd, or <10^th customized birthweight centile, versus those born >10^th centile (controls). We also did a further analysis, comparing those born at these low birthweight cut-offs versus those born appropriate for gestational age (10^th-89^th birthweight centile). Analyses were carried out using Mann-Whitney U. We had ethics approval for this study and all participants provided written, informed consent (Auckland, New Zealand Regional Ethics Committee: AKX/02/00/364).<h4>Results</h4>In women with plasma samples at 20 weeks' gestation there were 1756 controls and 189 who birthed <10^th centile birthweight (among these, 48 were <3^rd centile). Baseline clinical characteristics and pregnancy outcomes are shown in table 1. Compared to controls, SPINT1 levels were significantly reduced among pregnancies that ended with birth of neonates <10^th centile birthweight (P=0.006; Figure 1a), or <3^rd centile birthweight (P=0.005; Figure 1b). Among those with plasma samples at 15 weeks' gestation there were 1807 controls and 199 who birthed <10^th centile birthweight (among these, 54 birthed <3^rd centile, See supplementary table 1 for baseline characteristics). Compared to controls, plasma SPINT1 levels were significantly reduced among those who birthed <10^th (P=0.02; Figure 1c) or <3^rd birthweight centiles (P=0.004; Figure 1d). Our findings were similar when we compared SPINT1 concentrations among pregnancies that ended with birth of neonates <3^rd or 10^th birthweight centile, compared to those that ended with birth of neonates with a birthweight appropriate for gestational age (supplementary table 2).<h4>Conclusion</h4>Circulating levels of SPINT1 are low at 15 and 20-weeks' gestation preceding low birthweight deliveries. As birthweight may reflect fetal growth restriction in utero, our findings lend further evidence that fetal growth restriction may have its pathogenic origins as early as the first half of pregnancy. When considering our findings together with what is known about SPINT1¹, low levels across pregnancy may play a mechanistic role driving placental insufficiency. Given there is a consistent association between low SPINT1 across pregnancy^1,2 and low birthweight, SPINT1 merits further investigation as a clinical biomarker, perhaps combined with ultrasound or other circulating factors.