Treasurer Wayne Swan is being urged to smooth the ''sudden death'' end of the baby bonus, due to fall from $5000 to $500.

When the bonus was first introduced on July 1, 2004, Australian labour wards experienced their busiest Thursday in three decades.

Unconcerned: Wayne Swan does not think women will bring forward births to cash in on the baby bonus. Credit:Getty Images

A record 1005 babies were born on July 1, compared with 500 the day before, one of the quietest Wednesdays on record.

Melbourne University economist Joshua Gans found the babies born in July 2004 were significantly more likely to be ''overcooked''. About 680 babies were born weighing more than four kilograms in that month, 140 more than in a typical month.