Risk for Severe Morning Sickness Increased in Women Whose Mothers Had the Condition

Nancy Fowler Larson

May 04, 2010

May 4, 2010 — Women whose mothers suffered from hyperemesis gravidarum, or a potentially fatal degree of morning sickness, during pregnancy are 3 times more likely to experience the condition during their own pregnancies, according to a study published online April 30 in the British Medical Journal.

At least half of all pregnant women endure some nausea and vomiting, and from 0.5% to 2% have hyperemesis, which is characterized by excessive nausea and vomiting during the first 21 weeks of pregnancy. Hyperemesis can result in dehydration, nutritional shortages, weight loss, ketosis, and psychological distress. It has been associated with low birth weight, prematurity, and maternal and fetal deaths.

"To extend our understanding of the aetiology of this condition we examined the risk of hyperemesis according to whether or not the women and men under study were born after pregnancies complicated by hyperemesis," write Ase Vikanes, PhD student, Epidemiology Department, Norwegian Institute of Public Health, Oslo, and colleagues. "In addition, we estimated the risk of hyperemesis in women born after pregnancies not complicated by hyperemesis but where their mothers had hyperemesis in a previous or later pregnancy."

Using available data from 2.3 million Norwegian births between 1967 and 2006, the researchers selected 544,087 units of mothers and childbearing daughters and 399,777 units of mothers and female partners of child-producing sons. All births were single. Hospital admission was not required for a designation of hyperemesis, even though hyperemesis is the chief cause of hospitalization in early pregnancy.

The results showed that, among the original mothers of childbearing daughters, the incidence of hyperemesis was 0.68% (3704 of 544,087). Other findings were as follows:

  • Daughters born to mothers with hyperemesis during that pregnancy had a 3% chance of experiencing the condition during their own pregnancy, but those delivered by mothers whose pregnancy was unaffected by hyperemesis had a 1.05% risk (unadjusted odds ratio [OR], 2.9; 95% confidence interval [CI], 2.35 - 3.57).

  • The risk for women carrying the fetuses of sons born after pregnancies affected by hyperemesis was 1.18% compared with a 1.13% risk for those whose partners' mothers' pregnancies were not complicated by hyperemesis (unadjusted OR, 1.04; 95% CI, 0.68 - 1.58).

  • Daughters whose mothers did not experience hyperemesis during that pregnancy but did have the condition during a prior pregnancy had a 3.08% risk compared with a 1% risk in those daughters whose mothers did not have the condition (unadjusted OR, 3.15; 95% CI, 1.55 - 6.41).

  • Daughters with mothers who had hyperemesis during a subsequent pregnancy had a risk of 2.99% compared with 0.83% (unadjusted OR, 3.70; 95% CI, 1.51 - 9.08).

The figures were unchanged after adjustment for factors, including the mother's age at childbirth.

"Hyperemesis gravidarum is more strongly influenced by the maternal genotype than the fetal genotype, though environmental influences along the maternal line cannot be excluded as contributing factors," the authors write.

A limitation to the study was a lack of data regarding factors such as body mass index, smoking habits, education, ethnicity, educational attainment, and ethnic background.

In an editorial accompanying the study, Catherine Nelson-Piercy, MD, consultant obstetric physician, Guy's and St Thomas' Foundation Trust, London, United Kingdom, noted that the findings support those of previous studies. She also said that the study's omission of recurrent hyperemesis necessitates further research.

"Interestingly the authors excluded families in which women had two pregnancies affected by hyperemesis, but in these families the risk of recurrence in the daughters was very high," Dr. Nelson-Piercy writes. "To explore the genetic predisposition to hyperemesis further, and perhaps identify candidate genes, it may be useful to study women with recurrent severe hyperemesis."

The results of the current research may promote a greater understanding of hyperemesis and help physicians provide better treatment, according to the study authors.

"It might lead to a better appreciation of the underlying biology and should stimulate research into the genetic aetiology," the authors write. "This, as well as an understanding of the psychological consequences of experiencing severe nausea and vomiting, could be helpful for clinicians who treat and counsel women with hyperemesis gravidarum."

The Norwegian Research Council supported the study. The study authors have disclosed no relevant financial relationships.

BMJ. 2010;340:c2050. Published online April 30, 2010.

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