Zofran Linked to 20% More Birth Defects in Australian Study

A study linking the use of Zofran in pregnancy with a 20% increased risk of birth defects was published in December 2013 by a team of researchers in Australia.

The study, “Off-Label Use of Ondansetron in Pregnancy in Western Australia,” was based on data from 96,968 births in 2002-2005.

During this time, Zofran was used by 251 pregnant women. Although only a small number of pregnant women used Zofran, there were five times as many pregnant women on Zofran in 2005 as there were in 2002. The reason is unclear because the guidelines did not change during the study period.

The researchers found a 20% increased risk of major birth defects among children exposed to Zofran during the first trimester, but the estimate was nonsignificant, based on small numbers, and imprecise.

The risk was similar to that found in a recent analysis of a Danish registry of pregnancies. One analysis of the registry found that Zofran increased the risk of birth defects by 12% (not statistically significant), while a second analysis involving nearly 900,000 pregnancies over a longer period of time found a 30% increased risk of birth defects.

The Australian researchers also linked Zofran with a 6-fold increased risk of kidney defects, described as “obstructive defects of renal pelvis and ureter,” but they cautioned that the study was too small to assess the risk of individual birth defects.

Obstructive defects of the ureter often cause a birth defect known as hydronephrosis, which involves swelling and distention of the kidneys due to urine backing up in a clogged urethra. Most cases of hydronephrosis are not serious, but untreated cases can cause kidney failure.