Maternal sleep latency during early pregnancy is linked to child intelligence scores

Pregnant people often experience changes in their sleep patterns, but the long-term effects of these disruptions on the developing fetus are not fully understood. A recent study suggests that maternal sleep difficulties, particularly taking a long time to fall asleep, are associated with slightly lower intelligence scores in children at age four. The research, published in the Journal of Child Psychology and Psychiatry, also points to specific metabolic chemicals in the pregnant person’s blood that might link poor sleep to offspring brain development.

Nearly half of pregnant individuals report experiencing poor sleep quality. During pregnancy, hormonal, physical, and psychological shifts can dramatically alter a person’s sleep and wake cycles. Concurrently, fetal brain development occurs at a rapid pace.

Because the developing brain is highly adaptable, it is sensitive to the prenatal environment. Prior research has connected maternal sleep problems to adverse outcomes like preterm birth and low birth weight. Animal models have indicated that maternal sleep deprivation alters fetal brain structures, specifically areas involved in memory and learning.

Human studies have also hinted at a connection between prenatal sleep and a child’s cognitive outcomes. Most of these investigations assessed sleep at only one point in time. Pregnancy involves distinct phases of neural system development, meaning the timing of sleep disruptions could influence the brain differently. The basic architectural structures of the brain form rapidly during the first trimester. While the third trimester involves brain growth and maturation, the groundwork laid earlier makes early-pregnancy exposures particularly impactful.

Sleep is a foundational biological process that regulates metabolism. Disrupted sleep can alter glucose processing, increase inflammation, and change how the body breaks down nutrients. Researchers Yun Huang and Jun Zhang of the Shanghai Jiao Tong University School of Medicine wanted to track how sleep patterns throughout all three trimesters related to child intelligence. They also aimed to identify specific chemical markers, or metabolites, that might explain this biological connection.

The researchers analyzed data from 1,870 mother and child pairs enrolled in the Shanghai Birth Cohort. During their first, second, and third trimesters, the pregnant participants completed questionnaires detailing their sleep habits. These surveys asked about sleep duration, subjective sleep quality, and sleep latency. Sleep latency is the amount of time it takes to transition from full wakefulness to sleep.

When the children reached four years of age, trained staff evaluated their intelligence using a standardized assessment called the Wechsler Primary and Preschool Scale of Intelligence. This test measures a child’s full-scale intelligence quotient, or IQ, alongside specific cognitive abilities. Verbal comprehension measures a child’s ability to access and apply acquired word knowledge. Fluid reasoning evaluates the capacity to detect underlying conceptual relationships and use reasoning to solve novel problems.

The researchers used statistical models to compare the maternal sleep data from each trimester with the children’s test scores. They adjusted their calculations to account for maternal age, education, physical activity, and family history of mental disorders.

The analysis showed an association between taking longer to fall asleep and lower cognitive scores. Longer sleep latency in the first trimester was linked to lower full-scale IQ and lower verbal comprehension scores. In the second trimester, longer sleep latency was associated with lower fluid reasoning scores. Sleep difficulties in the third trimester did not yield statistically significant associations with the children’s test scores.

Next, the researchers evaluated how consistent sleep patterns across the entirety of pregnancy related to child brain development. They used a statistical technique to group participants based on how their sleep quality changed from the first trimester to the third. This longitudinal approach allowed the team to see the cumulative impact of sleep struggles. They found that individuals who consistently experienced longer sleep latency throughout their entire pregnancy had children with lower full-scale IQ, verbal comprehension, and fluid reasoning scores at age four.

To understand the biological mechanisms behind these observations, the researchers looked at metabolites. Metabolites are small molecules produced when the body breaks down food, chemicals, or its own tissue. The team analyzed fasting blood samples taken from 1,461 of the pregnant participants during their first trimester.

The researchers conducted untargeted metabolomic profiling. Instead of looking for a few specific chemicals, this technique scans the blood for hundreds of small molecules simultaneously, providing a broad snapshot of the body’s metabolic state. After identifying 413 metabolites in the maternal serum, they used a “meet-in-the-middle” analytical strategy. They first looked for metabolites linked to maternal sleep factors, then looked for metabolites linked to child test scores, and finally focused on the overlapping chemicals that connected the two endpoints.

Three specific molecules emerged as potential mediators: inositol, indoleacrylic acid, and 4-hydroxyquinoline. Inositol is a sugar that is synthesized by the body and found in common foods like fruits and beans. It is transferred across the placenta to the fetus, where it contributes to neurotransmitter signaling. The researchers observed an indirect path where maternal sleep duration was linked to child fluid reasoning through changes in maternal inositol levels.

Indoleacrylic acid and 4-hydroxyquinoline are byproducts of tryptophan, an amino acid involved in producing sleep-regulating hormones like serotonin and melatonin. Poor sleep can alter how the body breaks down tryptophan, increasing inflammatory pathways and changing the availability of serotonin, a hormone essential for neuronal growth. The researchers found that sleep disturbances influenced offspring verbal comprehension via alterations in these two tryptophan-related molecules.

The study relied on self-reported questionnaires to assess maternal sleep. These surveys capture a person’s subjective perception of their rest, which might differ from objective measurements like brainwave monitoring or movement tracking devices. The metabolic analysis only tested blood samples from the first trimester. A person’s metabolic profile can fluctuate due to diet and physical activity, meaning a single measurement might not capture the full biological environment across the entire pregnancy.

The large number of metabolites tested also increases the mathematical risk of identifying false associations, requiring future studies to validate these specific chemical links. Most participants in this sample had a college degree, meaning the findings might not generalize to populations with different educational or socioeconomic backgrounds. Because sleep disturbances are sometimes a symptom of underlying psychiatric conditions, residual genetic or environmental factors could still influence the outcomes.

The study, “Maternal sleep disturbance during pregnancy and child intelligence quotient: A metabolome-wide association study in the Shanghai Birth Cohort,” was authored by Yun Huang, Fei Luo, Guanghai Wang, Ting Zhang, Lin Zhang, Lichun Fan, and Jun Zhang.