Scientific Studies on Morning Sickness and Baby Gender

Woman feeling morning sickness

The truth of being able to predict the gender of your baby by the severity of your morning sickness is veiled in the mystical origins of most old wives' tales. However, this pregnancy myth that there is a morning sickness gender link has some scientific evidence to support the women who continue to believe in it.

The Old Wives' Tale

According to this old wives' tale, if you have severe morning sickness, gender myths say you are more likely to deliver a girl. Like other pregnancy myths, this prediction has uncertain origins. However, women who swear by it or are looking for scientific proof of this passed-down belief keep it alive through ongoing internet discussions.

Scientific Evidence on Morning Sickness and Gender

A few studies found women who had severe morning sickness (hyperemesis gravidarum) had a 27 to 80 percent greater chance of having a girl than a boy. The following is a sample of these studies since 1999:

  • A Swedish study reported in the British journal, Lancet, in 1999 found that women with hyperemesis gravidarum were more likely to deliver female offspring than women who did not have severe morning sickness.
  • A Danish study, summarized in a letter to Lancet in 2000, showed there were more girls born to women admitted to hospital for hyperemesis than in the general population. The birth gender ratio was 1.0:0.87 girls to boys, compared to the usual average of 1.0:1.05 girls to boys in the general population.
  • A Boston University study published in the journal Epidemiology in 2001 showed women with hyperemesis delivered more girls than women without hyperemesis, regardless of whether they had to be hospitalized or not.
  • A study from Washington State of pregnant women, hospitalized between 1987 to 1996 for hyperemesis in the first trimester, was reported in 2004 in the journal BJOG: An International Journal of Obstetrics and Gynaecology. Compared to women not hospitalized for hyperemesis, these women were 50 percent more likely to deliver girls and had a birth gender ratio of 1.5:1.0 girls to boys. Women who were hospitalized three days or more had an 80 percent (1.8:1.0) greater chance of having a girl.
  • Dutch researchers published another study in the same BJOG journal in 2011. This was a statistical analysis of several previously published studies by which they found that women with hyperemesis overall had a 27 percent (1.27:1.0) greater likelihood of having a girl than a boy.

There are no studies comparing women with milder symptoms of morning sickness to those without morning sickness.

Possible Explanation Offered

Women who are pregnant with girls are thought to have a higher level of the pregnancy hormone human chorionic gonadotropin (HCG). Some researchers suppose that the higher HCG and/or the higher estrogen levels produced by female fetuses account for the greater severity of hyperemesis in those women.

Different Immune Response

There are observations that pregnant women carrying a girl versus a boy seem to get sicker from illnesses such as asthma. A recent study published in 2017 in Brain, Behavior, and Immunity suggests that the explanation might be a difference in the immune response. The researchers found that when exposed to bacteria in the lab, immune cells from the blood of women carrying female fetuses produced more inflammatory factors, cytokines, than those carrying male babies.

It is not clear whether the heightened inflammation contributes to symptoms such as severe morning sickness. More studies are needed to figure out whether you can rely on more severe symptoms from an illness during your pregnancy as a sign of carrying a girl.

Reality of Morning Sickness as a Gender Predictor

Does no morning sickness mean a boy? Does severe morning sickness mean a girl? Although these studies show some support for the myth that women battling morning sickness are more likely to have a girl, the reality is that the rest of the symptomatic women had boys. Therefore, this old wives' tale is not a dependable way to predict the gender of your baby. Go the conventional route and get an ultrasound if you are yearning to know, or wait for the delight of the surprise at birth. In the meantime, try natural remedies for morning sickness or look for foods that reduce it to keep nausea at bay.

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Scientific Studies on Morning Sickness and Baby Gender