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Zofran First Trimester Pregnancy Safety


The “off-label” morning sickness drug Zofran has been linked to higher rates of many first-trimester birth defects, including heart defects and cleft palate.

Zofran in the First Trimester of Pregnancy

The first trimester is defined as the first three months (or weeks 1 through 12) of pregnancy. It is the most critical period in fetal development, when the body and organ systems develop.

It is also a period of major changes in the mother’s body. About three-quarters of pregnant women suffer from morning sickness (nausea and vomiting), and 1% develop the most extreme form, Hyperemesis gravidarum.

Morning sickness usually starts around the 6th week of pregnancy and continues until the 14th week, but some women suffer throughout the entire pregnancy.

Zofran (ondansetron) is an anti-nausea drug that is used by about 1 million pregnant women every year. It is a popular “off-label” (unapproved) treatment for morning sickness, although there has been an FDA-approved drug called Diclegis on the market since 2013.

Zofran and Birth Defects in the First Trimester

Studies have found that Zofran rapidly crosses the placenta in “significant levels” and remains active in the fetus longer that it does in the mother’s body. This is concerning, because Zofran is a powerful medication that blocks serotonin signaling. During fetal development, serotonin plays a critical role in the development of many organ systems.

Some of the most serious birth defects occur in the first trimester, including heart defects. However, many heart defects are not diagnosed until after the baby is born because they baby receives oxygenated blood from its mother.

Another first-trimester birth defect, cleft palate occurs around the 10th week of pregnancy. The defect involves a split in the roof of the mouth, and it usually requires surgery. Cleft palate is not diagnosed until the baby’s first physical examination shortly after it is born.

Zofran First Trimester Birth Defects

  • Birth Defects: Zofran was linked to a 30% increased risk of major birth defects overall in a study published by Dr. Jon T. Anderesen, based on data from 900,000 pregnancies in Denmark from 1997-2010.
  • Heart Defects: Zofran doubled the risk of having a baby with a “hole in the heart” (septal defect), according to a study published in Reproductive Toxicology.
  • Cleft Palate: The risk of having a baby with cleft palate increased by 2.4-times when Zofran was used in the first trimester, according to a study published in Birth Defects Research.


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