Zofran is not approved or recommended for use during the first trimester of pregnancy. Recent studies suggest it may increase the risk of birth defects, especially heart defects and cleft palate.

Zofran and First Trimester Morning Sickness

Every year, about 1 million pregnant women use the anti-nausea drug Zofran (ondansetron) to treat morning sickness. At least 75% of pregnant women suffer from morning sickness during the first trimester, which is the first three months (or weeks 1 through 12) of pregnancy.

The term “morning sickness” is a misnomer — it can occur at any time of day or even last all day long. The nausea usually starts at around 6 weeks of pregnancy, but can begin as early as 4 weeks. It tends to get worse over the next four weeks and then resolve by the 14th week of pregnancy.

However, some women have symptoms that persist beyond the first trimester, or even throughout the entire pregnancy.

About 1% develop the most extreme type — Hyperemesis gravidarum — which can be life-threatening for both mother and child. Extreme morning sickness is characterized by persistent nausea, vomiting, dehydration, weight-loss, electrolyte imbalances, sleep problems, and more.

What Happens in the First Trimester?

The first trimester is the most crucial period in your baby’s development. By the end of the third month, your baby should have developed all of its organs. Most pregnant women will undergo several tests at the end of the first trimester to check for birth defects, but these tests cannot detect all defects.

For example, heart defects commonly occur in the first trimester. But because the baby receives oxygenated blood from its mother, a heart defect is not usually discovered until after the baby is born.

Another common first-trimester birth defect is cleft palate (“split in the roof of the mouth”), which occurs by the 10th week of pregnancy when tissue on the roof of the mouth fails to grow together. Like a heart defect, it is not usually diagnosed until the baby’s first examination after it is born.

Zofran First Trimester Safety Risks

  • Birth Defects: A study based on 900,000 pregnancies in Denmark linked the use of Zofran with a 30% increased risk of major birth defects.
  • Heart Defects: A study published by Reproductive Toxicology linked Zofran with a doubled risk of “hole in the heart” defects.
  • Cleft Palate: A study published in Birth Defects Research linked Zofran with a 2.4-fold increased risk of cleft palate.
  • And more


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