New research shows a strong link between nitrates in drinking water and babies being born underweight or prematurely.
The Otago University analysis is of major overseas studies including one involving one point four million births in California.
The lead researcher in the Californian study, Stanford University's Allison Sherris, says while the link between nitrates and blue baby syndrome has been known for a while, the one between the chemical and preterm births is not so well understood.
She told reporter Conan Young that her study, which focused on siblings, had important findings.
