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One supermarket chain thought pregnant women would make better wine tasters. See more pregnancy pictures.

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How does pregnancy affect the senses of smell and taste?

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When British supermarket chain Tesco asked pregnant women to come in and taste their wines in 2004, they weren't advocating fetal alcohol syndrome. Tesco's wine tasters don't drink the wines, but they swirl them in their mouths for taste and then sp­it them back out.

Why did Tesco want pregnant women, of all people, to do this? They were hoping to take advantage of pregnant women's noses and taste buds in order to procure the best wines for their customers.

Tesco's campaign was inspired by the chief wine taster at the chain, who became pregnant and reported that her experience in tasting wine became much more pronounced [source: Sample]. She's not alone in finding her senses shifted: Pregnancy books warn about the effect, and several studies in which women self-reported on their sensory perceptions ­found that a majority of women noticed a change.

One such study, published in 2004, asked more than 100 pregnant women to report on their senses at several points in their pregnancy, and 76 percent of respondents experienced a change in smell or taste [source: Nordin et al]. Two-thirds of the women reported increased smell sensitivity, but they also reported distortions in smells, phantom smells and abnormal tastes, including increased bitter sensitivity and decreased salt sensitivity [source: Nordin et al.]. Women experienced these effects mostly during the first trimester of pregnancy, though a smaller percentage reported changes at a later stage of pregnancy as well. After pregnancy, all changes to smell and taste perception disappeared.

­Unfortunately, scientists can't necessarily back up these reports with any hard data. When Tesco announced its plans, a doctor from Britain's Royal College of Obstetrics and Gynecology said there was no evidence for enhanced taste during pregnancy and criticized it as a publicity stunt that involved drinking during pregnancy [source: BBC]. But one smell expert countered that it's just too hard to study the effect, since each pregnant woman experiences the change differently [source: Sample]. Scientists have differed bitterly on the origins of these changes.

So why do so many women report this symptom? Is there any benefit to smell sensitivity, or is it just another thing that can make the nine months of pregnancy miserable? And can anything be done besides turning pregnant women into an army of drug-sniffing crime fighters? Find out on the next page.

Is this woman sniffing out the best foods for her baby?

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Heightened Senses During Pregnancy

Like many things during a pregnancy, the changes in a woman's senses are largely attributed to hormones. When women become pregnant, their levels of estrogen increase. Estrogen has been linked with an increased sense of smell in non-pregnant women as well. A 2002 study conducted by Philadelphia's Monell Chemical Senses Center showed that women of child-bearing age exhibited a greater sensitivity to odors than men. Groups with lower estrogen levels, like prepubescent girls and post-menopausal women, performed comparably with the men [source: Harvard Women's Watch].

So, as women's levels of estrogen rise and fall, their sense of smell may change. There's evidence that a woman's sniffer also changes during her menstrual cycle and at ovulation, as well as during pregnancy [source: Sample]. But scientists aren't exactly sure how (or if) estrogen creates the change in the nose or in the brain [sources: Harvard Women's Watch, Pletsch and Kratz].

Scientists also debate whether a pregnant woman's heightened senses serve any benefit to her or her unborn baby. Some researchers believe sensitivity to odors and taste causes morning sickness, benefiting the woman because she's rejecting foods containing chemicals and toxins harmful to the fetus [source: Nordin et al]. Scientists who subscribe to this theory say it explains why pregnant women are sensitive to the smell and taste of cigarettes, alcohol, bitter vegetables and caffeinated beverages such as coffee. Some data shows that women who experience nausea have a lower rate of miscarriage, suggesting that the nose is doing its job in keeping the baby safe [source: Stanford Report].

 

Other scientists would beg to differ. A 2004 study tested the hypothesis that because pregnant women have greater smell sensitivity, they would rate food items with toxins much more negatively. Did this turn out to be true? Not really. In the experiment, pregnant women didn't demonstrate any smell sensitivity at all. There was no evidence that they had higher smell sensitivity than non-pregnant women, and there were only small differences between women and men in general [source: Swallow et al]. Women also didn't rank the smells of the harmful products more negatively, and there was little correlation between smell rankings and nausea [source: Swallow et al].

The study's authors did mention that perhaps the nausea of morning sickness may come about when the product is actually tasted, not just smelled. A quarter of the women reported abnormal taste sensitivity in the early stages of pregnancy, including a heightened sensitivity to bitter items and a lowered sensitivity to salty items [source: Nordin et al]. Again, sensitivity to bitter items like coffee may be the body's way of protecting the unborn baby. Conversely, a decreased sensitivity to salt may help women to consume more salt, which in turn makes them thirstier and helps them consume the fluids and various nutrients they need to support the fetus [source: Nordin et al.].

Like changes in smell, changes in taste and why they happen have been hard for scientists to nail down. But when a cranky pregnant woman complains of these symptoms, it's probably best not to say there's no scientific evidence for what she's feeling. Instead, pregnant women should simply try to avoid the scents that aggravate them, which may involve allowing a spouse to do the cooking or politely asking a coworker to lay off the cologne. Pregnant women should try to leave the windows open when possible for ventilation, and they might see if the soothing scents of mint, lemon or ginger can offer them any relief [source: Murkoff].

Sniff around on the next page for other stories on pregnancy and the body.

Lots More Information

Sources

  • Bhagat, Des Raj, Aniece Chowdhary, Sanjeev Verma, Jyotsana. "Physiological Changes in ENT During Pregnancy." Indian Journal of Otolaryngology and Head and Neck Surgery. July-September 2006.
  • Brody, Jane E. "What Could Be Good About Morning Sickness? Plenty." New York Times. June 6, 2000. (July 15, 2008) http://query.nytimes.com/gst/fullpage.html?res=9D04EFD6163FF935A35755C0A9669C8B63&sec=&spon=&pagewanted=all
  • Gilbert, Avery N. and Charles Wysocki. "Quantitative Assessment of Olfactory Experience during Pregnancy." Psychosomatic Medicine. 1991. (July 15, 2008) http://www.psychosomaticmedicine.org/cgi/reprint/53/6/693.pdf
  • Kuga, Mutsumi, Minoru Ikeda, Kunio Suzuki and Shigeo Takeuchi. "Changes in Gustatory Sense During Pregnancy." Acta Otolaryngol. 2002.
  • Murkoff, Heidi. "Heightened Sense of Smell." What to Expect. (July 15, 2008) http://www.whattoexpect.com/pregnancy/symptoms-and-solutions/heightened-smell.aspx
  • "New evidence connects nausea to sense of smell." Stanford Report. Sept. 20, 2000. (July 15, 2008) http://www.stanford.edu/dept/news/news/2000/september20/Nausea-920.html
  • Nordin, Steven, Daniel A. Broman, Jonas K. Olofsson and Marianne Wulff. "A Longitudinal Descriptive Study of Self-reported Abnormal Smell and Taste Perception in Pregnant Women." Chemical Senses. 2004. (July 15, 2008) http://chemse.oxfordjournals.org/cgi/reprint/29/5/391
  • Pletsch, Pamela K. and Anna Thornton Kratz. "Why Do Women Stop Smoking During Pregnancy? Cigarettes Taste and Smell Bad." Health Care for Women International. 2004.
  • Sample, Ian. "Do pregnant women really make the best wine tasters?" The Guardian. March 25, 2004. (July 15, 2008) http://www.guardian.co.uk/science/2004/mar/25/food.thisweekssciencequestions
  • Swallow, Brain L., Stephen W. Lindow, Mo Aye, Ewan A. Masson, Cesarettin Alasalvar, Peter Quantick, Jon Hanna. "Smell perception during early pregnancy: no evidence of an adaptive mechanism." BJOG: an International Journal of Obstetrics and Gynaecology." January 2005.
  • "Tesco wine tasting plans slammed." BBC. March 22, 2004. (July 15, 2008) http://news.bbc.co.uk/2/hi/health/3558377.stm
  • ­ ­­"Vive la Difference: Women's Sense of Smell." Harvard Women's Health Watch. April 2002.