In view of the fact that reproduction is necessary for a population to continue to exist and for the passage of genes to occur, intuitively, one would assume that over time, a comfortable pregnancy would have been selected for in modern mammals.  However, this is not the case. One of the most prevalent examples of the absence of comfort during pregnancy is the occurrence of morning sickness in humans. Morning sickness is an ailment that occurs often in women who are in their early stages of pregnancy and is linked with the food aversions, nausea and vomiting that are often associated with pregnancy. Up to two-thirds of all pregnant women may suffer from any combination of these symptoms.For many years it was thought that nausea and vomiting during pregnancy was caused by an illness; however, this line of thought raised several serious question, most notably, would not a pathological infection be detrimental to the health of the baby? If this is true, why are the miscarriage and fetal death rates lower for women who experience some form of nausea and vomiting during pregnancy than for those who do not (Sherman and Flaxman, 2000)? There must be some way to explain this queasiness associated with pregnancy.

 “Morning sickness” is an improper term for several reasons.  First, women with NVP experience the symptoms and discomfort of NVP not only during the morning hours, but during all hours of the day equally (Ref. Figure 1). The intensity of the “sickness” will not be any greater in the morning than the other times of the day. “Pregnancy sickness” is another common and widely accepted term, but, as with “morning sickness,” the term sickness insinuates that there are pathogenic forces at work. There are several proper terms that may be used in place of morning sickness. First, emesis gravidarum is the Latin terminology meaning “nausea alone or the combination of nausea, retching and the occasional vomiting in early pregnancy (Sherman and Flaxman, 2000).” The more severe form of this would be hyperemesis gravidarum, from which approximately 1% or less of all pregnant women suffer. However, the most widely accepted term for this is Nausea and Vomiting during Pregnancy, as it describes the occurrence very well (Sherman and Flaxman, 2000).

 However, it is found that even healthy women have this malady and despite having NVP, they will have healthy babies (Sherman and Flaxman, 2000). There has been some data showing that a certain bacteria, Heliocobacter pylori, may be to blame. Unfortunately, there is little research done in this field save for one staggering statistic: in a particular study, Heliocobacter pylori infected 89% of pregnant women with severe NVP in the study group, in contrast, only 7% of those who were free of NVP were infected (Pirisi, 1272). Heliocobacter pylori has also been known to cause several gastrointestinal tract disorders such as duodenal ulcer disease and gastric ulcers (www.helico.com). There are several questions left to be answered before this line of thought can be viewed more seriously. For example, are the bacteria more prevalent before or after the onslaught of NVP? Also, why would bacteria that causes gastrointestinal diseases be more prevalent in pregnant women?

 Throughout the years, man has sought to find ways of suppressing all human suffering, even when it may not be the best solution to do so. One of the greatest examples can be found in the context of NVP. In 1953, a sedative was synthesized named Thalidomide, and in 1958 it was marketed to the public. This was viewed as the wonder sedative of its time, as it was nearly impossible to commit suicide while using the drug. Also, it was found to have additional benefits, one of which was its effectiveness in quelling the nausea associated with pregnancy. As a result, women began to use this drug to keep these symptoms under control. However, beginning in 1961 until 1962, the offspring of the women who took this medication had at times severe birth defects. However, the fact that the medical community was aware of the teratogenic properties of Thalidomide, as well as the fact that it caused peripheral neuritis. It was believed at that time that the placenta was a superior barrier. “Medical students were taught that the human placenta gave perfect protection to the fetus and was impervious to toxic substances except in such large doses that they killed the mother (Dally, 1197).” Of course since this time, we have made leaps and bounds in medical research, and most women tend to steer clear of all dangerous medication when pregnant. For the women who experience the more extreme hyperemesis gravidarum, there have been some drugs made available, including one called Benedectin, which was the focus of a major lawsuit, but has now been exonerated as a completely safe drug. In fact, a generic version it is being sold in Canada without a prescription, and is going through FDA testing (NewsRx.com). However, is it a good idea to repress this nausea unless it is absolutely necessary?

 In 1992, a scientist by the name of Margie Profet wrote The Adapted Mind, in which she explained her views on NVP. She believed that a condition such as Nausea and Vomiting during Pregnancy was doubtfully pathogenic as it was very common, and quite spontaneous. She proposed that NVP was an adaptive evolutionary response to toxins that the mother would ingest during pregnancy. She argued that the food aversions, nausea, and vomiting was evolved in order to protect the developing fetus from toxins that many common foods have (Nesse and Williams, 1995). This would explain why a woman might enjoy steak before pregnancy; however, during pregnancy, the woman would recoil as if given a piece of refuse for dinner Spicy plant toxins and foods that have been produced by fungal and bacterial decomposition (cheese, for example) would be among the foods most avoided. Therefore, the women would tend to eat food that were more bland as foods with more flavor tend also have more toxins present. Profet described NVP as, “a lowering of the usual human threshold of tolerance to toxins in order to compensate for the extreme vulnerability of the embryo to toxins during organogenesis.” (Sherman and Flaxman, 2000) In fact, this may even explain why children tend to dislike vegetables and many other foods during their earlier years, and then grow to like them quite a bit, since they have high vulnerability to toxins during their early years. As they grow older they become less vulnerable to the potentially dangerous toxins, eventually try them, and due to this, broccoli and spinach are still being produced on farms around the world.

 The hypothesis laid out by Margie Profet seemed quite impressive and Cornell graduate student Samuel Flaxman and his post-doctorate advisor Paul Sherman set out in order to see whether it was correct. The two compiled data on nearly every study done on the subject. They devised the embryo hypothesis, which was very similar to Profet’s hypothesis yet much broader. This hypothesis had five critical predictions

1.)NVP should be associated with positive pregnancy outcomes.

2.)Foods that trigger NVP should contain teratogens, mutagens and abortifacients.

3.)NVP should be more common when the embryo is most sensitive to toxic chemicals.

4.)Foods containing toxins should be most aversive to women when embryonic organogenisis is most sensitive to disruption by exogenous chemicals.

5.)The frequency if NVP should depend on the diet of a population: symptoms should be uncommon in populations where staple foods rarely contain substances that could damage embryos.

 There were a number of interesting results from this study. First, there was the issue of time. They set out to, once and for all, show that the name morning sickness was indeed a misnomer. The two found that from the sixth week until the thirteenth week of pregnancy, the probability of NVP occurring was actually equal during any of the waking hours (0700 to 2300), while the number of women experiencing NVP dropped sharply during hours which are normally associated with sleep (2300 to 0700) (Ref. Figure 1). However, most importantly, there was not statistically significant difference in the occurrence of NVP during the four time frames that are considered waking hours; thus, “morning” sickness is proven to be a misnomer (Sherman and Flaxman, 2000).

Sherman and Flaxman also sought to discern what time frame NVP was most common. As expected it occurs most commonly in the first half of pregnancy. However, they did find some very interesting data. The number of women experiencing NVP jumped sharply during the fourth postmenstrual week, and peaked between the ninth and fourteenth postmenstrual week (Ref. Figure 2a, b). Interestingly, as NVP began to peak, so did organogenesis of embryonic structures. There are clear “critical periods” during which cell division, cell differentiation and specialization, as well as morphogenesis of many organ systems are at their most productive levels. However, this productivity comes at a price: a lack of protection from mutagens and teratogens. Thus, nausea, vomiting and food aversions all peak when organogenesis peaks so that the mother may protect the developing fetus from these harmful toxins (Ref. Figure 2c) (Sherman and Flaxman, 2000). They also found that one was more likely to experience NVP if one’s close relative, one’s mother or sisters for example, had experienced this as well.

Also, Sherman and Flaxman found some note-worthy information about complications in pregnancy and birth. The two found that pre-term births were less likely to occur when a woman experienced NVP, Birth weights were higher, neonates were more likely to survive for more than one month, and there were lower instances of congenital anomalies occurring. However, all of these occurred on irregular bases. There were other findings that were more concrete however. For instance, they found that women were much less likely to miscarry if they suffered from NVP (Ref. Figure 3), and fetal death was much less common if the woman experienced NVP (Ref. Figure 4). Also, women were twice as likely to miscarry or experience the occurrence fetal death if they were NVP absent as opposed to suffering nausea only. If they experienced vomiting, they were one-fourth as likely to miscarry, and one-half as likely for the fetus to die (Ref. Figure 5). This must mean that NVP serves a vital role in the survival of the fetus.

Finally, Sherman and Flaxman found a great deal about the types of foods that pregnant women tend to crave or avoid. They found that of all the studies, a range of 62% to 80% of pregnant women experienced an aversion of some sort. Meat, fish, poultry, and eggs were the most avoided food during pregnancy, followed by non-alcoholic beverages, and vegetables. The least avoided foods were dairy and ice cream, sweets, desserts, and chocolate, and finally the least avoided foods were grains and starches and fruit and fruit juices. As far as cravings go, fruit juices were most craved, followed by sweets, desserts, and chocolate. At the opposite end of the cravings spectrum were ethnic, strong and spicy foods, non-alcoholic beverages, and the least craved, not surprisingly, was alcoholic beverages (Ref. Table 1 & 2, Figure 6). There were also specifications between food cravings in each trimester. They found that aversions were greatest in the first trimester and in all but a few cases dropped steadily as the term wore on (Ref. Figure 7). Cross-cultural differences were prevalent as well. Flaxman and Sherman found that in societies where NVP was not present, the population was more likely to have staple foods that were:
 

1.) Only plants
2.) Corn as a staple
3.) Corn as the only staple
4.) Significantly less likely to have meat as a staple
5.) Slightly less likely to have rice as a staple

In retrospect, it is obvious that nausea and vomiting in pregnancy plays a vital role in the protection of the fetus. At this point in time Sherman and Flaxman’s embryo protection hypothesis, which built off the ideas of many with the same idea before them, such as Margie Profet, is the best available option for explaining the occurrence of NVP. It explains why the miscarriage and fetal death rates for women experiencing the symptoms for NVP are lower than the rates of the miscarriages and fetal deaths of those women who do no experience NVP. In fact, the embryo protection hypothesis satisfies all five of the critical predictions necessary. First, NVP was associated with positive pregnancy outcomes in every single study done (Sherman and Flaxman, 2000). Second, they found that most of the foods that women had aversions to were those that contained phytochemicals. Brussel sprouts, for example, contain isothiocyanates; these break down products of glucosinolates, which can cause chromosomal anomalies and aberrations (Sherman and Flaxman, 2000). These types of foods were also the ones most avoided, thus strengthening Sherman and Flaxman’s argument. It also proved that NVP was more apparent when organogenesis was in its most critical states. The last of the predictions involves cultures and societies. Since it has been shown that in societies where there is a lesser need for the symptoms of NVP due to diets lacking teratogens, these societies are less likely to suffer from NVP. I personally believe that this is, to say the least, a feasible way of thinking.

Figure 2.Proportions of Women with NVP vs. Organogenesis 

Figure 4. Association between NVP and Reduced Fetal Death.

Table 1.Food Aversions per woman by food type
 

Meat, Fish, Poultry and Eggs (Meat)	0.28 aversions per woman
Non-Alcoholic Beverages (N-A)	0.16 aversions per woman
Vegetables (Veg)	0.08 aversion per woman
Alcoholic Beverages (Alc)	0.04 aversions per woman
Ethnic, Strong and Spicy Foods (ESS)	0.04 aversions per woman
Dairy and Ice Cream (D)	<0.04 aversions per woman
Sweets, Desserts, and Chocolate (S)	<0.04 aversions per woman
Grains and Starches (G&S)	<0.02 aversions per woman
Fruit Juices (F)	<0.02 aversions per woman

Table 2.Food Cravings per woman by food type
 

Meat, Fish, Poultry and Eggs	0.12 cravings per woman
Non-Alcoholic Beverages	0.03 cravings per woman
Vegetables	0.06 cravings per woman
Alcoholic Beverages	<0.01 cravings per woman
Ethnic, Strong and Spicy Foods	0.04 cravings per woman
Dairy and Ice Cream	0.12 cravings per woman
Sweets, Desserts, and Chocolate	0.17 cravings per woman
Grains and Starches	0.08 cravings per woman
Fruit Juices	0.20 cravings per woman

Anonymous. (No Date Given). Information on Heliocobacter pylori. The Heliocobacter Pylori Foundation.Retrieved December 1, 2001 from the World Wide Web: http://www.helioco.com.

NewsRx.com. (2000) Morning Sickness Drug May Return. Women’s Health Weekly, 18-19.

Dally, A. (1998). Thalidomide: was the tragedy preventable?. The Lancet, 351, 1197-1199.

Flaxman, S. M. and Sherman P.W. (2000)Morning Sickness:A Mechanism for Protecting Mother and Embryo.Quarterly Review of Biology, 75 (2),113-148.

Nesse, R. M. and Williams, G. C. (1995). Why We Get Sick: The New Science of Darwinian Medicine. New York: Vintage.

Pirisi, A. (2001). Meaning of morning sickness sill unsettled. The Lancet, 357, 1270-1271.