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Lighter at six months, heavier at two: what mothers' sleep was linked to

Qurexa Editorial Team22 September 20267 min read 0 0
Lighter at six months, heavier at two: what mothers' sleep was linked to

What happened

Researchers in the United States have found a link between how well women sleep late in pregnancy and how their children grow over the following two years. The study came from the Keck School of Medicine at the University of Southern California. It was published in the American Journal of Preventive Medicine on 22 September 2026. The team followed 645 mother and child pairs taking part in a long-running Los Angeles pregnancy study called MADRES. They asked the mothers about their sleep in late pregnancy, using a standard questionnaire called the Jenkins Sleep Scale. They then tracked the children's height and weight through clinic visits and medical records. About 26% of the mothers reported poor sleep quality. That is roughly one in four. The pattern in their children was not what you might expect, and it changed over time. Babies born to mothers who slept badly weighed less from birth up to about six months old. Then it flipped. After the age of one to two years, those same children weighed noticeably more than the others. At one year, the difference was about 347 grams. At 17 months, it was about 752 grams. The effects were strongest in boys, and in babies born at full term. The lead author, Xiaoran Yang, said: "Poor sleep health in pregnancy is common and often overlooked." Monitoring it, the researchers suggest, "could be a simple and powerful step toward healthier growth". Senior author Carrie Breton suggested poor sleep may affect "maternal or child metabolic health programming" through several possible biological routes.

Why this matters

Sleep in pregnancy is usually treated as an inconvenience rather than a health measure. Everyone expects it to be bad. Very few people are asked about it at an antenatal appointment in any structured way. This study is part of a growing body of work suggesting that might be a missed opportunity. The pattern itself is interesting. Lighter early, heavier later is a shape that researchers have seen before in other contexts. It is sometimes called catch-up growth, and it has been linked with a higher chance of weight problems later in childhood. That is why a difference of a few hundred grams in a toddler is worth reporting. On its own, 752 grams is not much, and it would not worry a health visitor. It is the direction and the timing that interest researchers, not the size. There is also a practical angle. Unlike genetics or family history, sleep is something that can potentially be improved. If poor sleep in pregnancy really does influence a child's growth, then asking about it, and helping with it, becomes a cheap and low-risk thing to try. One more thing deserves saying clearly, because studies like this can land badly. Nothing here means a mother who slept badly has harmed her child. Poor sleep in late pregnancy is extremely common, largely unavoidable, and shaped by things well outside anyone's control, including physical discomfort, shift work and worry.

What the evidence actually says

This is an observational study. It follows people over time and looks for patterns. It cannot show cause. That is the single most important limitation, and it is worth spelling out why. Poor sleep in pregnancy is more common among people who are working long or irregular hours, who are under financial strain, who have other young children, or who live somewhere noisy or crowded. All of those things are also linked to childhood weight, independently of sleep. The researchers will have adjusted for some of these factors, but adjustment is never complete. Some of the pattern may reflect circumstances rather than sleep itself. Sleep was measured by questionnaire, not by any objective device. The Jenkins Sleep Scale is a recognised tool, but it records how people remember and describe their sleep. Late pregnancy is not a time when anyone assesses their own sleep neutrally. The sample is 645 mother-child pairs from one cohort in Los Angeles. That cohort is predominantly Hispanic and lower income by design, which is valuable because such groups are often under-studied, but it means the findings should not be assumed to transfer directly to the UK population. The weight differences are small. A few hundred grams is well within normal variation for an individual child. This is a finding about averages across a group, not a red flag for any one family. The subgroup findings, stronger effects in boys and in term births, are the kind of result that often does not repeat in other studies. They should be treated as a lead to follow, not a conclusion. What the study does well is track the same children over time with real measurements, rather than asking parents to recall weights. That prospective design is a genuine strength.

Practical advice

If you are pregnant, this is not a reason to worry about your sleep. Worrying about sleep is one of the reliable ways to sleep worse. But if sleep is genuinely difficult, it is worth mentioning at your next midwife appointment. It is often treated as something to put up with, and sometimes there is a treatable cause underneath. Things worth flagging specifically: heavy snoring or waking gasping, which can indicate sleep apnoea; restless, crawling sensations in the legs at night, which can be linked to low iron; heartburn that wakes you; and anxiety that keeps you awake. All of these have recognised approaches. From around 28 weeks, sleeping on your side is advised rather than on your back, and there is reasonable evidence behind that. A pillow between the knees or behind the back helps hold the position. Be careful with over-the-counter sleep remedies in pregnancy. Several are not recommended, including some sold as "natural". A pharmacist can tell you quickly what is safe, and that conversation is free. If you take regular medication and pregnancy is making it harder to get to a pharmacy, delivery is worth asking about. We provide that across Lincolnshire, and most pharmacies can arrange something similar. For children, the standard advice does not change. Health visitor checks track growth over time, and it is the trend that matters rather than any single measurement.

What to know

Researchers at the Keck School of Medicine, University of Southern California, followed 645 mother and child pairs. About 26% of mothers reported poor sleep quality in late pregnancy. Their babies weighed less from birth to six months, then more after age one to two: around 347 grams heavier at one year and 752 grams at 17 months. Effects were strongest in boys and in babies born at term. This is an observational study. It shows a link, not a cause, and the circumstances that cause poor sleep are themselves linked to childhood weight. Sleep was self-reported. The cohort was based in Los Angeles and is not a direct match for the UK population. The weight differences are small and are group averages, not warnings about individual children. The useful takeaway is simply that sleep in pregnancy is worth asking about, because some causes of poor sleep are treatable and are routinely missed. Sources: EurekAlert / Elsevier, "Mothers' poor sleep quality in late pregnancy linked to higher obesity risk in their children", 22 September 2026, https://www.eurekalert.org/news-releases/1143803; Yang, X. et al., American Journal of Preventive Medicine, 2026, https://doi.org/10.1016/j.amepre.2026.108546; Keck School of Medicine of USC, https://keck.usc.edu This article is for general information and does not replace advice from a doctor, midwife, pharmacist or other qualified healthcare professional. Always check with a professional before taking any medicine or supplement in pregnancy.

#pregnancy#sleep#child health#obesity#maternal health#research

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