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Risk Factors

Study findings vary widely in determining the women most at risk for HG. Cross-cultural studies vary greatly and typically study only one or two ethnic groups, but findings often show similar rates among women from different countries. Studies are limited by the inconsistent criteria for diagnosing HG and the availability for treatment worldwide.

In affected populations, it is more common in women who weigh more than 170 pounds, are nonsmokers, have twin (or more) pregnancies, trophoblastic disease, and are less than 20 years old. The risk may decrease after age 35. Hyperemesis is most common in first pregnancies and, contrary to current teaching, very often recurs in subsequent pregnancies in similar patterns. It has also been linked to women who have a diet high in fat. Epidemiological studies indicate that women with nausea and vomiting in pregnancy have a statistically significant decreased risk of miscarriage in the first 20 weeks, but may have a history of several spontaneous abortions (miscarriages).

Common risk factors include:

Untreated asthma
High saturated fat diet
Posttraumatic stress disorder (PTSD)
Excessive social stress (not a cause, but worses existing HG)
Multiple gestation (twins or more)
Food cravings and aversions before and during pregnancy
Epilepsy
History of:
- Nausea and vomiting during pregnancy
- Motion sickness
- Sensitivity to oral contraceptives
- Nausea premenstrually
- Migraine headaches
- Allergies
- Gall bladder disease
- Gastritis or ulcers
- Mother/sister with HG
- High blood pressure
- Liver disease
- Kidney disease
- Poor diet

Offsite Research:

Untreated Asthma:

The course and outcome of pregnancy in women with bronchial asthma.
Bahna SL, Bjerkedal T.
Acta Allergologica. 1972 Dec;27(5):397-406.

High saturated fat diet:

Saturated fat intake and the risk of severe hyperemesis gravidarum.
Signorello LB, Harlow BL, Wang S, Erick MA.
Epidemiology 1998 Nov;9(6):636-40.

Our results indicate that prepregnancy, high daily intake of total fat increases the risk of severe hyperemesis gravidarum (odds ratio = 2.9 for each 25 gm per day increase; 95% confidence interval = 1.4-6.0). This association is driven primarily by saturated fat intake [odds ratio = 5.4 for each 15 gm per day increase (equivalent to one quarter-pound cheeseburger); 95% confidence interval = 2.0-14.8].

Posttraumatic stress disorder:
NOTE: PTSD is also a largely unrecognized complication of HG that might in turn predispose women to greater morbidity in future pregnancies. Prevention of PTSD is better than treatment.

Posttraumatic stress disorder and pregnancy complications.
Seng JS, Oakley DJ, Sampselle CM, Killion C, Graham-Bermann S, Liberzon I.
Obstetrics and Gynecology 2001 Jan;97(1):17-22.

After controlling for demographic and psychosocial factors, women with posttraumatic stress disorder had higher odds ratios (ORs) for ectopic pregnancy (OR 1.7, 95% confidence interval [CI] 1.1, 2.8), spontaneous abortion (OR 1.9, 95% CI 1.3, 2.9), hyperemesis (OR 3.9, 95% CI 2.0, 7.4), preterm contractions (OR 1.4, 95% CI 1.1, 1.9), and excessive fetal growth (OR 1.5, 95% CI 1.0, 2.2). Pregnant women with posttraumatic stress disorder might be at higher risk for certain conditions, and assessment and treatment for undiagnosed posttraumatic stress might be warranted for women with those obstetric complications. Prospective studies are needed to confirm present findings and to determine potential biologic mechanisms. Treatment of traumatic stress symptoms might improve pregnancy morbidity and maternal mental health.

Excessive social stress:
NOTE: Social stress is more likely to exacerbate HG instead of cause it. Without the support of family members stress worsens HG, but doesn't cause it.

Paternal smoking:

Severe vomiting during pregnancy: antenatal correlates and fetal outcomes.
Zhang J, Cai WW.
Epidemiology. 1991 Nov;2(6):454-7.

One thousand eight hundred sixty-seven women with normal singleton live births were included in the analysis. The cumulative incidence of severe vomiting during pregnancy was 10.8%. Women with chronic liver disease had a threefold increased risk of severe vomiting during pregnancy. Paternal smoking was associated with a twofold increased risk of maternal vomiting. A modest association between severe vomiting and fetal growth retardation was identified (OR = 1.4, 95% CI: 0.9-2.3). Severe vomiting was also found to be associated with preeclampsia (OR = 1.5, 95% CI: 1.0-2.4). Our study indicates that passive smoking is a risk factor for vomiting during pregnancy, which may, in turn, increase the risk of fetal growth retardation.

Multiple gestation (twins or more):

Sex ratio and twinning in women with hyperemesis or pre-eclampsia.
Basso O, Olsen J.
The Danish Epidemiology Science Centre at the Department of Epidemiology and Social Medicine- Aarhus University, DK 8000 Aarhus C, DK.
Epidemiology 2001 Nov;12(6):747-9.

We examined twinning and fetal gender in births of women with a hospital diagnosis of pre-eclampsia or hyperemesis. We also investigated sex ratio in infants whose mothers had had hyperemesis or pre-eclampsia in a different pregnancy. From all the hospitalized cases in Denmark between 1980 and 1996 we extracted 6,227 births with hyperemesis and 24,764 with pre-eclampsia. Twins were more frequent in pregnancies with either condition. The male to female sex ratio was 1.04 (95%CI = 1.02-1.05) in the reference population, 0.87 (95% CI = 0.82-0.91) in births with hyperemesis, and 1.10 (95% CI = 1.07-1.12) in births with pre-eclampsia. Women with pre-eclampsia had slightly more males also in non-affected pregnancies.

Food cravings and aversions before and during pregnancy:

Morning sickness and salt intake, food cravings, and food aversions.
Crystal SR, Bowen DJ, Bernstein IL.
Department of Psychology, University of Washington, Seattle 98105, USA.
Physiology and Behavior 1999 Aug;67(2):181-7

Women reported more aversions during, than prior to, pregnancy. Women with more severe vomiting reported a greater number of aversions both prior to and during pregnancy. There was a significant association between experiencing cravings and aversions prior to pregnancy and experiencing craving and aversions during pregnancy.

Epilepsy:

Epilepsy and pregnancy.
Crawford P.
Special Centre for Epilepsy, York, UK.
Seizure 2002 Apr;11 Suppl A:212-9.

Pregnancies in women with epilepsy are high risk and need careful management by both the medical and obstetric teams due to the increased incidence of complications and adverse outcomes of pregnancy. There appears to be a minor but significant increased risk of maternal complications in women with epilepsy such as hyperemesis gravidarum, pre-eclampsia and eclampsia, vaginal bleeding and premature labour. In the majority of women seizure control will not alter during pregnancy. Oral vitamin K should be given to the mother receiving enzyme-inducing antiepileptic drugs.

Pathophysiology of the gastrointestinal tract during pregnancy.
Singer AJ, Brandt LJ.
American Journal of Gastroenterology. 1991;86:1695-1712.

Hyperemesis gravidarum.
Abell TL, Riely CA.
Gastroenterology Clinics of North America. 1992;21:835-49.

Updated on: Sep. 15, 2022