Perhaps Mother Nature got it right after all. It seems pregnant women are supposed to become anemic in order to give birth to large, healthy babies.

This shattering discovery turns on its head all the advice given to expectant mothers for generations.

Anemia in pregnancy has been seen as a major "problem", affecting up to half of all pregnant women.

Severe anemia, recognized by a fall in hemoglobin blood levels, has resulted in blood transfusions being given; otherwise, the condition has been treated with iron, folic acid or B12 supplements.

But new research, carried out by three medical colleges in London, has discovered that low concentrations of hemoglobin actually resulted in the birth of a healthy baby who went to term. In fact, risks of a preterm baby or one born with a low birth weight increased seven times in women whose hemoglobin levels failed to fall.

Women who had the healthiest babies had hemoglobin levels fall as low as 86 g/l. The World Health Organization has recommended that intervention is necessary when levels fall to just 110 g/l.

The next safest group in the study were women whose hemoglobin levels were between 95 and 105 g/l, still well inside the WHO's danger zone.

These astonishing discoveries are based on the records of 153,602 pregnant, mainly white, women, although the findings are true for all ethnic groups. The study team, headed by Philip Steer, suggests that hemoglobin levels need to fall below 105 g/l before the risk of a preterm baby are reduced.

!ABMJ, February 25, 1995.