We’ve all experienced vomiting at some stage in our lives, whether it’s from a nasty bout of food poisoning or the well-known norovirus that episodically spreads through the population. And everyone can agree that it’s horrendous.
However, imagine if ongoing nausea and vomiting were expected for a significant phase in your life, and how that would affect you physically, mentally and emotionally. This is the reality for the four in five women who develop nausea and vomiting during pregnancy. Even in milder cases, this means unpleasant symptoms like queasiness, lack of appetite, and throwing up.
For the three per cent of women who develop a condition called hyperemesis gravidarum, things are even worse, requiring hospital admission and treatment.
Hyperemesis gravidarum is a collection of symptoms including severe nausea and vomiting that a woman cannot normally eat or drink, resulting in dehydration, nutrient deficiency and weight loss – putting both mother and baby’s life at risk.
According to the Office of National Statistics, In 2022 this led to nearly 20,000 women being admitted to hospital.
Yet until recently hardly anything was known about the cause of nausea and vomiting in pregnancy. Anecdotes suggest that the more nausea and vomiting you experienced, the healthier the pregnancy – and even that it was related to the number of babies you were pregnant with.
However, real-world evidence shows there is no truth to this. In fact, there is a wide range of severity and patterns of nausea and vomiting throughout pregnancy.
Although it’s often called ‘morning sickness’, nausea and vomiting in pregnancy can occur at any time day or night. It is typically worse in the first 12 weeks and then settles down. But for many women, it persists throughout the whole pregnancy.
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However, there has been a breakthrough, after over 20 years of work in this area, to determine the causality. This has been driven by Dr Marlena Fejzo, a geneticist at the University of Southern California Keck School of Medicine.
Fejzo was motivated to do this work since she suffered very badly from nausea and vomiting during her second pregnancy in 1999. She was unable to eat or drink without vomiting, rapidly lost weight, and became too weak to stand or walk.
Yet her doctor was dismissive, suggesting she was exaggerating her symptoms to get attention. Fejzo was eventually hospitalised and miscarried at 15 weeks.
Working with a private company, 23 and Me, which enables individuals to send their own DNA sample to determine health and ancestry insights, Fejzo conducted a genetic study with women who had previously been pregnant.
She determined an association between women who suffered from severe nausea and vomiting in pregnancy (requiring intravenous fluids) and a variant in a gene coding for a protein named GDF15, a hormone that acts on the brainstem.
This association pinpointed where further research was needed: to understand the role of GDF15 protein in pregnancy.
GDF15 is secreted from the placenta in the first two trimesters of pregnancy. It also likely plays a role in preventing the mother from biologically rejecting the baby, and so is vital in enabling the pregnancy to continue. However, GDF15 has been shown to be a regulator of physiological body weight and appetite via the brain. It is overproduced in people with cancer who suffer from severe appetite and weight loss.
Adding to the previous study, research led by Fejzo and the University of Cambridge's Prof Sir Stephen O’Rahilly found that high levels of GDF15 were found in women with severe nausea and vomiting during pregnancy. However, the effect of the hormone seemed to be dependent on the women’s sensitivity and pre-pregnancy exposure to GDF15. Women who had high exposure pre-pregnancy had no nausea or vomiting symptoms despite having high levels of GDF15 hormone.
It is hypothesised that prolonged exposure to GDF15 before pregnancy could have a protective effect, making women less sensitive to the sharp surge in the hormone caused by the developing baby.
This exposure relationship is quite unique and provides not only more understanding and knowledge but also suggests a potential treatment – by increasing exposure to the hormone pre-pregnancy, women could be desensitized. Much like how some people are treated for dietary allergies through controlled exposure therapy.
Like nausea and vomiting in pregnancy, many common conditions affecting women are poorly understood despite their incidence being very high. The healthcare of women is not niche, and there is so much more to understand and learn through this type of research.
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