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Monday 26 August 2019

Morning Sickness (Things We Don’t Know about Pregnancy Series #1)

Recently, I’ve needed to take a lie down after every meal. This isn’t because I have a food baby – it’s because I’m having an actual baby, and that’s when morning sickness really hits me.

Numbers vary, but reports suggest two thirds or more women will experience some sort of morning sickness – which can include vomiting, nausea, food aversions, and feeling “under the weather”.

Most women get it between weeks 6 and 14 in the first trimester of pregnancy, but some get it earlier, have it fade sooner, or suffer it for most of the 9 months they are carrying. Some never get it. Some women suffer all hours of the night and day (I like to think the objectionable term “morning sickness” refers not to a propensity to suffer only in the mornings, but to the sickness as the “beginning” or “dawn” of pregnancy or motherhood), and some find it comes and goes throughout the day or even week to week. Some get it at specific times of day, or have it triggered by brushing their teeth, particular foods, or particular smells (I didn’t think smell affected me until someone walked past me on a train with one of those heavily processed Cornish pasties!). Unfortunately, we don’t know what causes morning sickness, nor why it varies so much woman to woman.

What causes morning sickness? Image via Wikipedia Commons.

There is a predictive factor though – if you get morning sickness once, you have a 75-85% chance of getting it with a further pregnancy[1]. And it’s linked to cultural diet. One cross-cultural study found 7 traditional societies that had no history of morning sickness, and noted that they were significantly less likely to include animal products in their diets than 20 other traditional societies that had[2].

Then it’s not only humans who get it. In a study of 202 female rhesus monkeys, it was found they systematically rejected foods or certain foods both whilst they were ovulating and in early pregnancy, peaking around week 5[3]. Other animals, such as rats, show different patterns in female food rejection.

Pregnancy health


Morning sickness is the most common “pregnancy complication” – but is it really an illness? Women who feel sick have a higher probability of a healthy pregnancy, and lower probability of spontaneous abortion.

Having said that, my grandma had two healthy pregnancies, but was lucky enough to avoid morning sickness both times. Equally, some expectant mothers suffer from Hyperemesis Gravidarum, which makes the woman so sick she is at risk of dehydration, malnutrition, and even death. That doesn’t sound healthy to me! We don’t know what causes Hyperemesis Gravidarum, but risk factors include a first pregnancy, multiple pregnancy, obesity, history of eating disorder, or family history of Hyperemesis Gravidarum.


The cause of morning sickness is unknown, but it is believed to be something to do with the placenta, because it’s whilst the placenta’s forming that most women experience morning sickness and, once it’s formed, that the sickness fades away.
There are three main theories for why women experience morning sickness:

  1. Prophylaxis – the embryo protects itself by making the mother averse to potentially dangerous foods.
    In particular, women experience aversions to strong-tasting vegetables, caffeine and alcohol, which are potentially abortifacient, and, even more strongly, to animal products such as meat and eggs, which carry a high risk of parasites and pathogens when she is immunosuppressed.
    Studies have shown symptoms peak when the embryo is most vulnerable to chemicals[2].
  2. By-product – sickness is a nasty side effect that serves no direct purpose, caused by mother and baby competing over essential resources or the hormones associated with viable pregnancies.
    This theory has had little scrutiny, and studies that have looked into it have not found supporting evidence[4].
    However, elevated hCG hormone levels (and reductions in some other thyroid chemicals) have been positively correlated with morning sickness[5].
  3. Social indicator – letting others know a woman is pregnant to ward of sexual partners and increase social support.
    There seems to be nothing in the literature at all about this!
It’s also worth noting that, when ill, your body, not the microorganisms, make you feel “under the weather” – and the reason for this is to encourage you to rest and give your body the best chance of recovery. Tiredness and nausea often go hand in hand during pregnancy, and most women need extra sleep.

Relieving morning sickness

Ginger is a good remedy for all kinds of sickness, but we don't know why. Image via Wikipedia Commons.

Some women lose weight during morning sickness, but there’s no reason they should unless they are throwing up very frequently – because the one agreed solution to morning sickness is eating. Usually eating something dry, basic, and not particularly nutritiously fulfilling, like crackers. Why? We don’t know, but this advice is ubiquitous, and seems to work. But it’s strange… Feel carsick and start on the sweets in the glove compartment? Got a nasty tummy bug and reach for the ice cream? We rarely want to eat when we feel sick for other reasons, and if we do, it usually makes things worse: so why is morning sickness different?

Other advice does have a reason behind it, such as eat when you wake up and in multiple small meals across the day to stabilise your blood sugar levels. But most supposed remedies are controversial or, at the very least, still a mystery. Such as ginger, used for centuries as a sickness remedy, and still unexplained – or sea bands, which apply acupressure, an eastern medical technique that currently remains unsupported by scientific evidence, and which usually comes mixed up with ideas such as bodily energy. Both of these seem to work subjectively for most people, but not all. We don’t know why, but some studies suggest acupressure can be attributed to placebo effect (others disagree).

Another controversial remedy is vitamin B6, which comes with both studies showing no effect[6], and studies showing effectiveness in treating morning sickness[7].


The most mysterious thing I’ve found about morning sickness is its apparent predictive power over your offspring’s salt preferences. Studies in infants[8] and adults[9] have correlated how sick expectant mothers got with how much their offspring like salt, and found it statistically significant. There appears to be no explanation for this!

If your mother suffered terrible morning sickness, you're more likely to enjoy salty foods. Image via Wikipedia Commons.

There are many unknowns when it comes to pregnancy, and over the next few months, I’ll be exploring more of them with you. Look out for my next blog post, which will be about weight.

To read our full article on the things we don't know about pregnancy, check out our site. This article will be updated as we add posts across the coming months.

why don't all references have links?

[1] Maltepe, Caroline. Surviving morning sickness successfully: from patient's perception to rational management. Journal of Population Therapeutics and Clinical Pharmacology 21.3 (2014).
[2] Flaxman, Samuel M., and Paul W. Sherman. Morning sickness: a mechanism for protecting mother and embryo. The Quarterly review of biology 75.2 (2000): 113-148.
[3] Czaja, John A. "Food rejection by female rhesus monkeys during the menstrual cycle and early pregnancy." Physiology & behavior 14.5 (1975): 579-587.
[4] Flaxman, Samuel M., and Paul W. Sherman. Morning sickness: adaptive cause or nonadaptive consequence of embryo viability? The American Naturalist 172.1 (2008): 54-62.
[5] Mori, M. A. S. A. O., et al. Morning sickness and thyroid function in normal pregnancy. Obstetrics and gynecology 72.3 Pt 1 (1988): 355-359.
[6] Schuster, K., et al. Morning sickness and vitamin B6 status of pregnant women. Human nutrition. Clinical nutrition 39.1 (1985): 75-79.
[7] Chittumma, Porndee, Kasem Kaewkiattikun, and Bussaba Wiriyasiriwach. Comparison of the effectiveness of ginger and vitamin B6 for treatment of nausea and vomiting in early pregnancy: a randomized double-blind controlled trial. Journal-medical association of thailand 90.1 (2007): 15.
[8] Crystal, Susan R., and Ilene L. Bernstein. Infant salt preference and mother's morning sickness. Appetite 30.3 (1998): 297-307.
[9] Crystal, Susan R., and Ilene L. Bernstein. Morning sickness: impact on offspring salt preference. Appetite 25.3 (1995): 231-240.

1 comment:

  1. Congratulations on the pregnancy Rowena! Looking forward to reading the rest of these :)