Amniotic fluid rubidium concentration association with newborn birthweight: a maternal-neonatal pilot study.

Background: Although most biological systems, including human tissues, contain rubidium, its biogeochemical functions and possible role in neonatal birthweight are largely unknown. An animal study indicated a correlation between rubidium deficiency in the maternal diet and lower newborn birthweight.

Objective: This pilot study measured rubidium concentrations in amniotic fluid during the second trimester of (low-risk) pregnancy and investigated potential correlations between rubidium levels and third-trimester newborn birthweight-small for gestational age, appropriate for gestational age, and large for gestational age-and between preterm birth and term birth in uncomplicated pregnancies.

Study Design: This prospective, single-center study investigated a possible relationship between rubidium concentration in second-trimester amniotic fluid and third-trimester birthweight percentile. Amniotic fluid (at a median gestational age of 19 weeks) was sampled to determine rubidium concentration. Maternal and newborn characteristics were obtained from participant and delivery records.

Results: After screening 173 pregnant women, 99 amniotic fluid samples were evaluated. Midpregnancy median rubidium concentrations were significantly lower among newborns that were classified as small for gestational age than among newborns that were classified as appropriate for gestational age (106 vs 136 μg/L; P<.01). Based on a logistic regression random forest model, amniotic fluid rubidium was identified as a significant contributing factor to appropriate-for-gestational-age birthweight with 54% of the total contribution.

Conclusion: Amniotic fluid rubidium concentration seems to be a strong predictor of appropriate-for-gestational-age birthweight and a potential marker for newborn birthweight classifications. In particular, low rubidium concentrations in amniotic fluid during midpregnancy are linked to third-trimester lower birthweight percentile. These findings could potentially serve as a valuable tool for early identification of pregnancy outcomes. Further investigation is necessary to fully explore the effect of rubidium on fetal development.