Originally published 2019-05-20.
Morning sickness affects most pregnant women to some degree, usually in the first trimester.
Does morning sickness mean your baby will be clever? Not in any way that predicts an individual child. A small 2009 study from Toronto found that children whose mothers had nausea and vomiting in pregnancy scored somewhat higher, on average, on several intelligence and language tests at ages three to seven. A separate 2016 study linked nausea in early pregnancy with a lower chance of pregnancy loss. Both findings are real associations, but neither turns a symptom into a forecast, and having no nausea is not a bad sign.
Morning sickness is miserable for many women, so it is easy to see why a hopeful headline spread quickly. Here is what the research actually measured, what it cannot tell us, and what helps when nausea is hard to bear.
Inside the 2009 Toronto study
The research came from the Motherisk Program at the Hospital for Sick Children (SickKids) in Toronto and was led by Dr Irena Nulman. It was published in The Journal of Pediatrics in 2009 and was described at the time as the first study of its kind.
The team followed 121 mother and child pairs, with pregnancies between 1998 and 2003, in three groups:
- mothers with morning sickness who took the anti-nausea drug Diclectin (doxylamine with vitamin B6);
- mothers with morning sickness who did not take it;
- mothers who had no morning sickness.
When the children were between three and seven years old, they were tested for performance IQ, verbal fluency, phonological processing and numerical memory. The researchers adjusted for the mothers' alcohol use and socioeconomic status. Children of mothers who had had morning sickness scored higher on these measures, and more severe symptoms went with higher scores.
A main purpose of the study was reassurance: it found no sign that the anti-nausea medicine harmed children's development. The authors themselves called for more research rather than presenting nausea as a promise of a gifted child.
What the study cannot tell you
A study of 121 families is small. Groups that size can produce differences that shrink or vanish in larger samples, and the result has not become an established rule in later pregnancy guidance. Several other things limit what it can show:
- Association is not cause. Women who feel very sick may differ in other ways, such as hormone levels, age or how many previous pregnancies they had, that also relate to children's outcomes.
- Averages are not individuals. Many children of mothers with no nausea score very highly, and many children of mothers with severe nausea score around the average.
- IQ at age three to seven is only a snapshot. Scores at that age are influenced by home environment, sleep, schooling and the testing day itself.
Older versions of this story said the study "demonstrated" that nausea is "a great sign" of a high IQ. That overstates it. The fair summary is that one study found a modest average difference worth investigating further.
The 2016 study on pregnancy loss
The second study often bundled with this story is about something different. Stefanie Hinkle and colleagues at the US National Institute of Child Health and Human Development published it in JAMA Internal Medicine in September 2016. It was a secondary analysis of the EAGeR trial, in which women who had already had one or two pregnancy losses recorded their symptoms daily, before any loss happened.
Among these women, nausea, and especially nausea with vomiting, was associated with a lower chance of losing the pregnancy. Because symptoms were logged in real time, the study avoided a common flaw of older research, where women were asked to remember symptoms afterwards. Hinkle also stressed that "not all pregnancies are the same and everyone is different": many women with no nausea at all have healthy pregnancies.
Why might nausea go with good outcomes?
Nobody knows for certain, and the 2016 authors said the mechanisms still needed research. The most common explanation involves hormones. In early pregnancy the placenta produces human chorionic gonadotropin (hCG), the hormone detected by pregnancy tests; it rises steeply in the first trimester, around the same time nausea peaks. (Some earlier write-ups called it "GCH", a mix-up of the letters.) Higher hCG may reflect a well-functioning placenta, and a healthy placenta matters for the baby's growth, including the brain.
Another long-discussed idea, proposed by evolutionary biologists, is that nausea and food aversions may protect the embryo by steering mothers away from strong-tasting foods that could carry toxins or germs during the most sensitive weeks of development. Both explanations are hypotheses, not proven facts, and neither means that nausea itself makes a child smarter.
Nausea usually eases by the middle of pregnancy. Photo: avemario / Depositphotos.
Common myths about morning sickness
- "It only happens in the morning." It can strike at any time of day or night.
- "No nausea means something is wrong." Plenty of women have healthy pregnancies without it. The NHS notes that ordinary morning sickness does not put the baby at increased risk, and its absence is not a warning sign on its own.
- "Severe vomiting is just part of a healthy pregnancy." Most nausea is harmless, but a severe form called hyperemesis gravidarum can cause dehydration and malnutrition and may need hospital treatment.
- "It lasts the whole pregnancy." For most women it settles somewhere between weeks 16 and 20.
Coping with nausea, and when to get help
The NHS suggests simple steps that many women find useful: rest, avoid smells and foods that trigger nausea, eat small plain snacks often (dry toast, crackers, rice), try cold foods if hot cooking smells are a problem, and sip fluids little and often. Some people find ginger or wrist acupressure bands helpful; check with a pharmacist before taking ginger supplements.
Anti-sickness medicines that are considered safe in pregnancy exist, and the Toronto study is one of several that found no harm to children from the medicine its mothers took. Whether medicine is right for you is a decision to make with your doctor or midwife.
Talk to a doctor or midwife promptly if you cannot keep food or fluids down for 24 hours, have very dark urine or none for more than eight hours, feel very weak or faint, have stomach pain or a fever, vomit blood, or are losing weight.
If you are struggling with morning sickness, the research offers some comfort: it is common, it usually passes, and it is often a sign that pregnancy hormones are doing their job. It is not, however, a test score for your future child, and feeling well is nothing to worry about.
Sources: Nulman et al., The Journal of Pediatrics, 2009; Maclean's, April 2009: Mother's morning sickness linked to child's IQ; Hinkle et al., JAMA Internal Medicine, 2016; MedicalResearch.com, September 2016: interview with Stefanie Hinkle; NHS: Vomiting and morning sickness in pregnancy. Photos: Rawpixel / Depositphotos (preview); avemario / Depositphotos.
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