Dec. 10, 1999 (Atlanta) -- The following statement is likely to offend about half the people reading this: Girl babies may cause a greater incidence of severe morning sickness among pregnant women than boy babies. And following that line of thought, if a woman is very sick during her first trimester, should she just go ahead and paint the baby's room pink? Well, don't get the color palettes out just yet.
In the Dec. 10 issue of the journal The Lancet, Swedish researchers from the Karolinska Institute in Stockholm present a study of over one million pregnant women that shows those who suffered severe morning sickness during the first trimester were more likely to have girls than boys. This was not typical morning sickness but a condition called hyperemesis gravidarum, which is morning sickness that's bad enough to require hospitalization.
The investigators looked at all Swedish births from 1987 to 1995 and found that the ratio of girls to boys was about 49% to 51%. Among those women 5,900 were admitted to the hospital with severe morning sickness during the first three months of pregnancy; they had more girls than boys (56% girls to 44% boys). Women who became ill after the first trimester returned to the more equal ratio of boys to girls.
The thinking, according to lead investigator Johan Askling, MD, goes like this: There is a hormone present in pregnancy called human chorionic gonadotropin (hCG). This is a variant of the hormone used to signal pregnancy in home pregnancy tests. Though no one knows what causes morning sickness, some research suggests the hormone might play a part in the nausea, Askling tells WebMD. Since studies have also indicated a slight difference in hCG among boy and girl fetuses, the researchers decided to see if there was a connection between sex ratio, the hormone and severe nausea.
"We believe that there is something causing morning sickness that is more common among female pregnancies, like human chorionic gonadotropin," Askling tells WebMD. "Studies performed in later pregnancy beyond the first trimester have shown a slight sex difference in the main level of this hormone, so that female pregnancies tend to have a slightly higher level of this hormone, and we speculated ... that if the same sex difference in this hormone level exists in the early part of the pregnancy, and if this hormone is truly related to the occurrence of morning sickness, then we would perhaps expect an altered sex ratio among women suffering from severe nausea."
A key word there is "speculation". Askling made it clear that their "hypothesis does not rest on firm ground." But it does perhaps lay the groundwork for future studies. "I think that's how one should look at our results. Our results don't clear the mist and show a big sequence of events, but they add an extra piece of information or some extra knowledge about what is going on in early pregnancy," Askling tells WebMD.
Askling and colleagues write that an important limitation to the study is the lack of specific knowledge about what caused the women to become sick. "Non-medical factors may contribute to hospital admission," according to the researchers.
So, should women start thinking 'sugar and spice' when they're feeling anything but nice? "This by no means is a way for the individual couple to determine the sex of their offspring. This is purely a statistical phenomenon that can only be proved or shown in large groups," Askling tells WebMD. "We've studied a million births, where a number of thousands of women had this very severe morning sickness. So, we have studied women at one end of the spectrum. Extrapolating from there, to an individual expectant woman, would be stupid, and you cannot really do that, and as illustrated by our study, almost half of the women with severe nausea did eventually give birth to boys, so the predictive value of this, for the individual mother, is not much better than tossing a coin."
Sharon Phelan, MD, an associate professor at the University of Alabama at Birmingham, mentioned some of the same limitations Askling did. She says the accuracy of the diagnosis about the woman's severe morning sickness "creates additional confusion" because the definition of hyperemesis isn't "straightfoward".
Phelan says she doesn't know if the study has "an adequate sample size to make that conclusion" because although there were one million births, the speculation is based on about 5,900 pregnant women. Then there are the odds: "He [the researcher] is saying it's 56 to 44, and those are almost 50-50 odds, it's not that different."
Beyond modern techniques, most of what people use to determine a child's sex are "old wives' tales," Phelan tells WebMD. And as Askling did, she worries that "this [information] could be potentially misused."
"What are you going to do with that information? The fear would be that if you had some sort of a marker test that at six weeks into the pregnancy you could tell with very good accuracy the sex of the baby, the fear would be: would people selectively choose which pregnancies they would continue to carry based on something as basic as gender?