Most pregnancy nausea is uncomfortable but temporary. Hyperemesis gravidarum is different.
A large Stanford Medicine study of nearly 2.5 million California births found that pregnant women who received emergency department or inpatient care for hyperemesis gravidarum, or HG, faced higher risks for several pregnancy and birth complications. The findings do not mean ordinary morning sickness is dangerous, and they do not prove HG caused the complications. But they suggest that severe, sustained nausea and vomiting may be an important warning sign that a pregnancy needs closer medical attention.
HG is a severe form of pregnancy nausea and vomiting that can interfere with eating, hydration, weight gain and nutrient intake. While 70% to 80% of pregnant women experience some nausea, HG affects an estimated 1% to 3% of pregnancies.
“Hyperemesis gravidarum is not just bad morning sickness; it’s severe enough to cause dehydration and significant weight loss,” said lead study author Rebecca Gardner, a Stanford Medicine graduate student in epidemiology and clinical research.
The study, published in the American Journal of Epidemiology, looked at single-baby births in California from 2007 to 2011. Researchers compared pregnancies in which the mother received emergency department or inpatient care for HG with pregnancies that did not involve HG-related hospital care.
Of the 2,476,492 births included in the analysis, 53,681, or 2.2%, were to mothers with HG severe enough to require emergency or hospital care.
After adjusting for possible confounding factors, women with HG were about 18% more likely to have preeclampsia, about 25% more likely to deliver early, about 37% more likely to be anemic and about 14% more likely to experience placental abruption than women without HG. The study also found higher risk for gestational hypertension and babies who were small for their gestational age.
“We found hyperemesis gravidarum was linked to higher risk for preterm birth, anemia, smaller-than-expected babies, preeclampsia, gestational hypertension and placental abruption,” Gardner said.
The risks were higher among women first hospitalized for HG during the second trimester than among those hospitalized during the first trimester.
Researchers said one possible explanation involves nourishment early in pregnancy. Women with HG may struggle to keep food and fluids down at a time when hydration, weight gain and key nutrients such as folate matter for fetal and placental development.
“We know from other studies that women with HG don’t get as many nutrients,” Gardner said.
That does not mean HG inevitably leads to complications. Most pregnancies involving HG still result in healthy outcomes. But the findings suggest the condition should not be dismissed as something pregnant women simply have to endure.
Because the study relied on medical records, it cannot prove that HG directly caused the pregnancy and birth complications. It also focused on more severe cases that led to emergency department or inpatient care, not mild or moderate nausea managed outside the hospital. The data came from births between 2007 and 2011, before treatment guidance changed in 2018 to encourage faster and more aggressive treatment of pregnancy nausea and vomiting.
Still, the size of the study makes its findings notable. Earlier studies on HG and pregnancy outcomes were often smaller or based largely on European populations.
“For physicians, I think this data means that pregnancies with HG hospitalization may warrant closer monitoring for certain complications,” Gardner said.
For pregnant women, the message is not to panic, but to speak up. Severe nausea and vomiting, dehydration, significant weight loss or trouble getting enough food and fluids should be taken seriously and discussed with a health care professional.
“Pregnant women need to know that most HG pregnancies still result in healthy outcomes for the mom and baby, but HG does need to be taken seriously,” Gardner said.
This research was funded by a grant from the National Heart, Lung, and Blood Institute.